<feed xmlns='http://www.w3.org/2005/Atom'>
<title>lwn.git/include/uapi/linux, branch docs-5.14</title>
<subtitle>Linux kernel documentation tree maintained by Jonathan Corbet</subtitle>
<id>http://mirrors.hust.edu.cn/git/lwn.git/atom?h=docs-5.14</id>
<link rel='self' href='http://mirrors.hust.edu.cn/git/lwn.git/atom?h=docs-5.14'/>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/'/>
<updated>2021-05-08T15:31:46+00:00</updated>
<entry>
<title>Merge tag 'net-5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net</title>
<updated>2021-05-08T15:31:46+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2021-05-08T15:31:46+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=fc858a5231089b972076642a86cf62481d95d82e'/>
<id>urn:sha1:fc858a5231089b972076642a86cf62481d95d82e</id>
<content type='text'>
Pull networking fixes from Jakub Kicinski:
 "Networking fixes for 5.13-rc1, including fixes from bpf, can and
  netfilter trees. Self-contained fixes, nothing risky.

  Current release - new code bugs:

   - dsa: ksz: fix a few bugs found by static-checker in the new driver

   - stmmac: fix frame preemption handshake not triggering after
     interface restart

  Previous releases - regressions:

   - make nla_strcmp handle more then one trailing null character

   - fix stack OOB reads while fragmenting IPv4 packets in openvswitch
     and net/sched

   - sctp: do asoc update earlier in sctp_sf_do_dupcook_a

   - sctp: delay auto_asconf init until binding the first addr

   - stmmac: clear receive all(RA) bit when promiscuous mode is off

   - can: mcp251x: fix resume from sleep before interface was brought up

  Previous releases - always broken:

   - bpf: fix leakage of uninitialized bpf stack under speculation

   - bpf: fix masking negation logic upon negative dst register

   - netfilter: don't assume that skb_header_pointer() will never fail

   - only allow init netns to set default tcp cong to a restricted algo

   - xsk: fix xp_aligned_validate_desc() when len == chunk_size to avoid
     false positive errors

   - ethtool: fix missing NLM_F_MULTI flag when dumping

   - can: m_can: m_can_tx_work_queue(): fix tx_skb race condition

   - sctp: fix a SCTP_MIB_CURRESTAB leak in sctp_sf_do_dupcook_b

   - bridge: fix NULL-deref caused by a races between assigning
     rx_handler_data and setting the IFF_BRIDGE_PORT bit

  Latecomer:

   - seg6: add counters support for SRv6 Behaviors"

* tag 'net-5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net: (73 commits)
  atm: firestream: Use fallthrough pseudo-keyword
  net: stmmac: Do not enable RX FIFO overflow interrupts
  mptcp: fix splat when closing unaccepted socket
  i40e: Remove LLDP frame filters
  i40e: Fix PHY type identifiers for 2.5G and 5G adapters
  i40e: fix the restart auto-negotiation after FEC modified
  i40e: Fix use-after-free in i40e_client_subtask()
  i40e: fix broken XDP support
  netfilter: nftables: avoid potential overflows on 32bit arches
  netfilter: nftables: avoid overflows in nft_hash_buckets()
  tcp: Specify cmsgbuf is user pointer for receive zerocopy.
  mlxsw: spectrum_mr: Update egress RIF list before route's action
  net: ipa: fix inter-EE IRQ register definitions
  can: m_can: m_can_tx_work_queue(): fix tx_skb race condition
  can: mcp251x: fix resume from sleep before interface was brought up
  can: mcp251xfd: mcp251xfd_probe(): add missing can_rx_offload_del() in error path
  can: mcp251xfd: mcp251xfd_probe(): fix an error pointer dereference in probe
  netfilter: nftables: Fix a memleak from userdata error path in new objects
  netfilter: remove BUG_ON() after skb_header_pointer()
  netfilter: nfnetlink_osf: Fix a missing skb_header_pointer() NULL check
  ...
</content>
</entry>
<entry>
<title>Merge branch 'akpm' (patches from Andrew)</title>
<updated>2021-05-07T07:34:51+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2021-05-07T07:34:51+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=a48b0872e69428d3d02994dcfad3519f01def7fa'/>
<id>urn:sha1:a48b0872e69428d3d02994dcfad3519f01def7fa</id>
<content type='text'>
Merge yet more updates from Andrew Morton:
 "This is everything else from -mm for this merge window.

  90 patches.

  Subsystems affected by this patch series: mm (cleanups and slub),
  alpha, procfs, sysctl, misc, core-kernel, bitmap, lib, compat,
  checkpatch, epoll, isofs, nilfs2, hpfs, exit, fork, kexec, gcov,
  panic, delayacct, gdb, resource, selftests, async, initramfs, ipc,
  drivers/char, and spelling"

* emailed patches from Andrew Morton &lt;akpm@linux-foundation.org&gt;: (90 commits)
  mm: fix typos in comments
  mm: fix typos in comments
  treewide: remove editor modelines and cruft
  ipc/sem.c: spelling fix
  fs: fat: fix spelling typo of values
  kernel/sys.c: fix typo
  kernel/up.c: fix typo
  kernel/user_namespace.c: fix typos
  kernel/umh.c: fix some spelling mistakes
  include/linux/pgtable.h: few spelling fixes
  mm/slab.c: fix spelling mistake "disired" -&gt; "desired"
  scripts/spelling.txt: add "overflw"
  scripts/spelling.txt: Add "diabled" typo
  scripts/spelling.txt: add "overlfow"
  arm: print alloc free paths for address in registers
  mm/vmalloc: remove vwrite()
  mm: remove xlate_dev_kmem_ptr()
  drivers/char: remove /dev/kmem for good
  mm: fix some typos and code style problems
  ipc/sem.c: mundane typo fixes
  ...
</content>
</entry>
<entry>
<title>treewide: remove editor modelines and cruft</title>
<updated>2021-05-07T07:26:34+00:00</updated>
<author>
<name>Masahiro Yamada</name>
<email>masahiroy@kernel.org</email>
</author>
<published>2021-05-07T01:06:44+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=fa60ce2cb4506701c43bd4cf3ca23d970daf1b9c'/>
<id>urn:sha1:fa60ce2cb4506701c43bd4cf3ca23d970daf1b9c</id>
<content type='text'>
The section "19) Editor modelines and other cruft" in
Documentation/process/coding-style.rst clearly says, "Do not include any
of these in source files."

I recently receive a patch to explicitly add a new one.

Let's do treewide cleanups, otherwise some people follow the existing code
and attempt to upstream their favoriate editor setups.

It is even nicer if scripts/checkpatch.pl can check it.

If we like to impose coding style in an editor-independent manner, I think
editorconfig (patch [1]) is a saner solution.

[1] https://lore.kernel.org/lkml/20200703073143.423557-1-danny@kdrag0n.dev/

Link: https://lkml.kernel.org/r/20210324054457.1477489-1-masahiroy@kernel.org
Signed-off-by: Masahiro Yamada &lt;masahiroy@kernel.org&gt;
Acked-by: Geert Uytterhoeven &lt;geert@linux-m68k.org&gt;
Reviewed-by: Miguel Ojeda &lt;ojeda@kernel.org&gt;	[auxdisplay]
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
</entry>
<entry>
<title>Merge tag 'vfio-v5.13-rc1pt2' of git://github.com/awilliam/linux-vfio</title>
<updated>2021-05-06T21:22:58+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2021-05-06T21:22:58+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=a2de4bbddce3e98bd2444bb027dc84418a0066b1'/>
<id>urn:sha1:a2de4bbddce3e98bd2444bb027dc84418a0066b1</id>
<content type='text'>
Pull more VFIO updates from Alex Williamson:
 "A second small set of commits for this merge window, primarily to
  unbreak some deletions from our uAPI header.

   - Additional mdev sample driver cleanup (Dan Carpenter)

   - Doc fix (Alyssa Ross)

   - Unbreak uAPI from NVLink2 support removal (Alex Williamson)"

* tag 'vfio-v5.13-rc1pt2' of git://github.com/awilliam/linux-vfio:
  docs: vfio: fix typo
  vfio/pci: Revert nvlink removal uAPI breakage
  vfio/mdev: remove unnecessary NULL check in mbochs_create()
</content>
</entry>
<entry>
<title>Merge tag 'riscv-for-linus-5.13-mw0' of git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux</title>
<updated>2021-05-06T16:24:18+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2021-05-06T16:24:18+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=939b7cbc00906b02c6eae6a380ad6c24c7a1e043'/>
<id>urn:sha1:939b7cbc00906b02c6eae6a380ad6c24c7a1e043</id>
<content type='text'>
Pull RISC-V updates from Palmer Dabbelt:

 - Support for the memtest= kernel command-line argument.

 - Support for building the kernel with FORTIFY_SOURCE.

 - Support for generic clockevent broadcasts.

 - Support for the buildtar build target.

 - Some build system cleanups to pass more LLVM-friendly arguments.

 - Support for kprobes.

 - A rearranged kernel memory map, the first part of supporting sv48
   systems.

 - Improvements to kexec, along with support for kdump and crash
   kernels.

 - An alternatives-based errata framework, along with support for
   handling a pair of errata that manifest on some SiFive designs
   (including the HiFive Unmatched).

 - Support for XIP.

 - A device tree for the Microchip PolarFire ICICLE SoC and associated
   dev board.

... along with a bunch of cleanups.  There are already a handful of fixes
on the list so there will likely be a part 2.

* tag 'riscv-for-linus-5.13-mw0' of git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux: (45 commits)
  RISC-V: Always define XIP_FIXUP
  riscv: Remove 32b kernel mapping from page table dump
  riscv: Fix 32b kernel build with CONFIG_DEBUG_VIRTUAL=y
  RISC-V: Fix error code returned by riscv_hartid_to_cpuid()
  RISC-V: Enable Microchip PolarFire ICICLE SoC
  RISC-V: Initial DTS for Microchip ICICLE board
  dt-bindings: riscv: microchip: Add YAML documentation for the PolarFire SoC
  RISC-V: Add Microchip PolarFire SoC kconfig option
  RISC-V: enable XIP
  RISC-V: Add crash kernel support
  RISC-V: Add kdump support
  RISC-V: Improve init_resources()
  RISC-V: Add kexec support
  RISC-V: Add EM_RISCV to kexec UAPI header
  riscv: vdso: fix and clean-up Makefile
  riscv/mm: Use BUG_ON instead of if condition followed by BUG.
  riscv/kprobe: fix kernel panic when invoking sys_read traced by kprobe
  riscv: Set ARCH_HAS_STRICT_MODULE_RWX if MMU
  riscv: module: Create module allocations without exec permissions
  riscv: bpf: Avoid breaking W^X
  ...
</content>
</entry>
<entry>
<title>Merge branch 'akpm' (patches from Andrew)</title>
<updated>2021-05-05T20:50:15+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2021-05-05T20:50:15+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=8404c9fbc84b741f66cff7d4934a25dd2c344452'/>
<id>urn:sha1:8404c9fbc84b741f66cff7d4934a25dd2c344452</id>
<content type='text'>
Merge more updates from Andrew Morton:
 "The remainder of the main mm/ queue.

  143 patches.

  Subsystems affected by this patch series (all mm): pagecache, hugetlb,
  userfaultfd, vmscan, compaction, migration, cma, ksm, vmstat, mmap,
  kconfig, util, memory-hotplug, zswap, zsmalloc, highmem, cleanups, and
  kfence"

* emailed patches from Andrew Morton &lt;akpm@linux-foundation.org&gt;: (143 commits)
  kfence: use power-efficient work queue to run delayed work
  kfence: maximize allocation wait timeout duration
  kfence: await for allocation using wait_event
  kfence: zero guard page after out-of-bounds access
  mm/process_vm_access.c: remove duplicate include
  mm/mempool: minor coding style tweaks
  mm/highmem.c: fix coding style issue
  btrfs: use memzero_page() instead of open coded kmap pattern
  iov_iter: lift memzero_page() to highmem.h
  mm/zsmalloc: use BUG_ON instead of if condition followed by BUG.
  mm/zswap.c: switch from strlcpy to strscpy
  arm64/Kconfig: introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
  x86/Kconfig: introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
  mm,memory_hotplug: add kernel boot option to enable memmap_on_memory
  acpi,memhotplug: enable MHP_MEMMAP_ON_MEMORY when supported
  mm,memory_hotplug: allocate memmap from the added memory range
  mm,memory_hotplug: factor out adjusting present pages into adjust_present_page_count()
  mm,memory_hotplug: relax fully spanned sections check
  drivers/base/memory: introduce memory_block_{online,offline}
  mm/memory_hotplug: remove broken locking of zone PCP structures during hot remove
  ...
</content>
</entry>
<entry>
<title>Merge tag 'thermal-v5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux</title>
<updated>2021-05-05T19:46:48+00:00</updated>
<author>
<name>Linus Torvalds</name>
<email>torvalds@linux-foundation.org</email>
</author>
<published>2021-05-05T19:46:48+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=583f2bcf86a322dc0387f5a868026d2e2fe18261'/>
<id>urn:sha1:583f2bcf86a322dc0387f5a868026d2e2fe18261</id>
<content type='text'>
Pull thermal updates from Daniel Lezcano:

 - Remove duplicate error message for the amlogic driver (Tang Bin)

 - Fix spellos in comments for the tegra and sun8i (Bhaskar Chowdhury)

 - Add the missing fifth node on the rcar_gen3 sensor (Niklas Söderlund)

 - Remove duplicate include in ti-bandgap (Zhang Yunkai)

 - Assign error code in the error path in the function
   thermal_of_populate_bind_params() (Jia-Ju Bai)

 - Fix spelling mistake in a comment 'disabed' -&gt; 'disabled' (Colin Ian
   King)

 - Use the device name instead of auto-numbering for a better
   identification of the cooling device (Daniel Lezcano)

 - Improve a bit the division accuracy in the power allocator governor
   (Jeson Gao)

 - Enable the missing third sensor on msm8976 (Konrad Dybcio)

 - Add QCom tsens driver co-maintainer (Thara Gopinath)

 - Fix memory leak and use after free errors in the core code (Daniel
   Lezcano)

 - Add the MDM9607 compatible bindings (Konrad Dybcio)

 - Fix trivial spello in the copyright name for Hisilicon (Hao Fang)

 - Fix negative index array access when converting the frequency to
   power in the energy model (Brian-sy Yang)

 - Add support for Gen2 new PMIC support for Qcom SPMI (David Collins)

 - Update maintainer file for CPU cooling device section (Lukasz Luba)

 - Fix missing put_device on error in the Qcom tsens driver (Guangqing
   Zhu)

 - Add compatible DT binding for sm8350 (Robert Foss)

 - Add support for the MDM9607's tsens driver (Konrad Dybcio)

 - Remove duplicate error messages in thermal_mmio and the bcm2835
   driver (Ruiqi Gong)

 - Add the Thermal Temperature Cooling driver (Zhang Rui)

 - Remove duplicate error messages in the Hisilicon sensor driver (Ye
   Bin)

 - Use the devm_platform_ioremap_resource_byname() function instead of a
   couple of corresponding calls (dingsenjie)

 - Sort the headers alphabetically in the ti-bandgap driver (Zhen Lei)

 - Add missing property in the DT thermal sensor binding (Rafał Miłecki)

 - Remove dead code in the ti-bandgap sensor driver (Lin Ruizhe)

 - Convert the BRCM DT bindings to the yaml schema (Rafał Miłecki)

 - Replace the thermal_notify_framework() call by a call to the
   thermal_zone_device_update() function. Remove the function as well as
   the corresponding documentation (Thara Gopinath)

 - Add support for the ipq8064-tsens sensor along with a set of cleanups
   and code preparation (Ansuel Smith)

 - Add a lockless __thermal_cdev_update() function to improve the
   locking scheme in the core code and governors (Lukasz Luba)

 - Fix multiple cooling device notification changes (Lukasz Luba)

 - Remove unneeded variable initialization (Colin Ian King)

* tag 'thermal-v5.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/thermal/linux: (55 commits)
  thermal/drivers/mtk_thermal: Remove redundant initializations of several variables
  thermal/core/power allocator: Use the lockless __thermal_cdev_update() function
  thermal/core/fair share: Use the lockless __thermal_cdev_update() function
  thermal/core/fair share: Lock the thermal zone while looping over instances
  thermal/core/power_allocator: Update once cooling devices when temp is low
  thermal/core/power_allocator: Maintain the device statistics from going stale
  thermal/core: Create a helper __thermal_cdev_update() without a lock
  dt-bindings: thermal: tsens: Document ipq8064 bindings
  thermal/drivers/tsens: Add support for ipq8064-tsens
  thermal/drivers/tsens: Drop unused define for msm8960
  thermal/drivers/tsens: Replace custom 8960 apis with generic apis
  thermal/drivers/tsens: Fix bug in sensor enable for msm8960
  thermal/drivers/tsens: Use init_common for msm8960
  thermal/drivers/tsens: Add VER_0 tsens version
  thermal/drivers/tsens: Convert msm8960 to reg_field
  thermal/drivers/tsens: Don't hardcode sensor slope
  Documentation: driver-api: thermal: Remove thermal_notify_framework from documentation
  thermal/core: Remove thermal_notify_framework
  iwlwifi: mvm: tt: Replace thermal_notify_framework
  dt-bindings: thermal: brcm,ns-thermal: Convert to the json-schema
  ...
</content>
</entry>
<entry>
<title>mm/vmscan: move RECLAIM* bits to uapi header</title>
<updated>2021-05-05T18:27:23+00:00</updated>
<author>
<name>Dave Hansen</name>
<email>dave.hansen@linux.intel.com</email>
</author>
<published>2021-05-05T01:36:01+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=b6676de8d7b48724d4cd3a3742c62fa525baa904'/>
<id>urn:sha1:b6676de8d7b48724d4cd3a3742c62fa525baa904</id>
<content type='text'>
It is currently not obvious that the RECLAIM_* bits are part of the uapi
since they are defined in vmscan.c.  Move them to a uapi header to make it
obvious.

This should have no functional impact.

Link: https://lkml.kernel.org/r/20210219172557.08074910@viggo.jf.intel.com
Signed-off-by: Dave Hansen &lt;dave.hansen@linux.intel.com&gt;
Reviewed-by: Ben Widawsky &lt;ben.widawsky@intel.com&gt;
Reviewed-by: Oscar Salvador &lt;osalvador@suse.de&gt;
Acked-by: David Rientjes &lt;rientjes@google.com&gt;
Acked-by: Christoph Lameter &lt;cl@linux.com&gt;
Cc: Alex Shi &lt;alex.shi@linux.alibaba.com&gt;
Cc: Daniel Wagner &lt;dwagner@suse.de&gt;
Cc: "Tobin C. Harding" &lt;tobin@kernel.org&gt;
Cc: Christoph Lameter &lt;cl@linux.com&gt;
Cc: Huang Ying &lt;ying.huang@intel.com&gt;
Cc: Dan Williams &lt;dan.j.williams@intel.com&gt;
Cc: Qian Cai &lt;cai@lca.pw&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
</entry>
<entry>
<title>userfaultfd: add UFFDIO_CONTINUE ioctl</title>
<updated>2021-05-05T18:27:22+00:00</updated>
<author>
<name>Axel Rasmussen</name>
<email>axelrasmussen@google.com</email>
</author>
<published>2021-05-05T01:35:49+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=f619147104c8ea71e120e4936d2b68ec11a1e527'/>
<id>urn:sha1:f619147104c8ea71e120e4936d2b68ec11a1e527</id>
<content type='text'>
This ioctl is how userspace ought to resolve "minor" userfaults.  The
idea is, userspace is notified that a minor fault has occurred.  It
might change the contents of the page using its second non-UFFD mapping,
or not.  Then, it calls UFFDIO_CONTINUE to tell the kernel "I have
ensured the page contents are correct, carry on setting up the mapping".

Note that it doesn't make much sense to use UFFDIO_{COPY,ZEROPAGE} for
MINOR registered VMAs.  ZEROPAGE maps the VMA to the zero page; but in
the minor fault case, we already have some pre-existing underlying page.
Likewise, UFFDIO_COPY isn't useful if we have a second non-UFFD mapping.
We'd just use memcpy() or similar instead.

It turns out hugetlb_mcopy_atomic_pte() already does very close to what
we want, if an existing page is provided via `struct page **pagep`.  We
already special-case the behavior a bit for the UFFDIO_ZEROPAGE case, so
just extend that design: add an enum for the three modes of operation,
and make the small adjustments needed for the MCOPY_ATOMIC_CONTINUE
case.  (Basically, look up the existing page, and avoid adding the
existing page to the page cache or calling set_page_huge_active() on
it.)

Link: https://lkml.kernel.org/r/20210301222728.176417-5-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen &lt;axelrasmussen@google.com&gt;
Reviewed-by: Peter Xu &lt;peterx@redhat.com&gt;
Cc: Adam Ruprecht &lt;ruprecht@google.com&gt;
Cc: Alexander Viro &lt;viro@zeniv.linux.org.uk&gt;
Cc: Alexey Dobriyan &lt;adobriyan@gmail.com&gt;
Cc: Andrea Arcangeli &lt;aarcange@redhat.com&gt;
Cc: Anshuman Khandual &lt;anshuman.khandual@arm.com&gt;
Cc: Cannon Matthews &lt;cannonmatthews@google.com&gt;
Cc: Catalin Marinas &lt;catalin.marinas@arm.com&gt;
Cc: Chinwen Chang &lt;chinwen.chang@mediatek.com&gt;
Cc: David Rientjes &lt;rientjes@google.com&gt;
Cc: "Dr . David Alan Gilbert" &lt;dgilbert@redhat.com&gt;
Cc: Huang Ying &lt;ying.huang@intel.com&gt;
Cc: Ingo Molnar &lt;mingo@redhat.com&gt;
Cc: Jann Horn &lt;jannh@google.com&gt;
Cc: Jerome Glisse &lt;jglisse@redhat.com&gt;
Cc: Kirill A. Shutemov &lt;kirill@shutemov.name&gt;
Cc: Lokesh Gidra &lt;lokeshgidra@google.com&gt;
Cc: "Matthew Wilcox (Oracle)" &lt;willy@infradead.org&gt;
Cc: Michael Ellerman &lt;mpe@ellerman.id.au&gt;
Cc: "Michal Koutn" &lt;mkoutny@suse.com&gt;
Cc: Michel Lespinasse &lt;walken@google.com&gt;
Cc: Mike Kravetz &lt;mike.kravetz@oracle.com&gt;
Cc: Mike Rapoport &lt;rppt@linux.vnet.ibm.com&gt;
Cc: Mina Almasry &lt;almasrymina@google.com&gt;
Cc: Nicholas Piggin &lt;npiggin@gmail.com&gt;
Cc: Oliver Upton &lt;oupton@google.com&gt;
Cc: Shaohua Li &lt;shli@fb.com&gt;
Cc: Shawn Anastasio &lt;shawn@anastas.io&gt;
Cc: Steven Price &lt;steven.price@arm.com&gt;
Cc: Steven Rostedt &lt;rostedt@goodmis.org&gt;
Cc: Vlastimil Babka &lt;vbabka@suse.cz&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
</entry>
<entry>
<title>userfaultfd: add minor fault registration mode</title>
<updated>2021-05-05T18:27:22+00:00</updated>
<author>
<name>Axel Rasmussen</name>
<email>axelrasmussen@google.com</email>
</author>
<published>2021-05-05T01:35:36+00:00</published>
<link rel='alternate' type='text/html' href='http://mirrors.hust.edu.cn/git/lwn.git/commit/?id=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5'/>
<id>urn:sha1:7677f7fd8be76659cd2d0db8ff4093bbb51c20e5</id>
<content type='text'>
Patch series "userfaultfd: add minor fault handling", v9.

Overview
========

This series adds a new userfaultfd feature, UFFD_FEATURE_MINOR_HUGETLBFS.
When enabled (via the UFFDIO_API ioctl), this feature means that any
hugetlbfs VMAs registered with UFFDIO_REGISTER_MODE_MISSING will *also*
get events for "minor" faults.  By "minor" fault, I mean the following
situation:

Let there exist two mappings (i.e., VMAs) to the same page(s) (shared
memory).  One of the mappings is registered with userfaultfd (in minor
mode), and the other is not.  Via the non-UFFD mapping, the underlying
pages have already been allocated &amp; filled with some contents.  The UFFD
mapping has not yet been faulted in; when it is touched for the first
time, this results in what I'm calling a "minor" fault.  As a concrete
example, when working with hugetlbfs, we have huge_pte_none(), but
find_lock_page() finds an existing page.

We also add a new ioctl to resolve such faults: UFFDIO_CONTINUE.  The idea
is, userspace resolves the fault by either a) doing nothing if the
contents are already correct, or b) updating the underlying contents using
the second, non-UFFD mapping (via memcpy/memset or similar, or something
fancier like RDMA, or etc...).  In either case, userspace issues
UFFDIO_CONTINUE to tell the kernel "I have ensured the page contents are
correct, carry on setting up the mapping".

Use Case
========

Consider the use case of VM live migration (e.g. under QEMU/KVM):

1. While a VM is still running, we copy the contents of its memory to a
   target machine. The pages are populated on the target by writing to the
   non-UFFD mapping, using the setup described above. The VM is still running
   (and therefore its memory is likely changing), so this may be repeated
   several times, until we decide the target is "up to date enough".

2. We pause the VM on the source, and start executing on the target machine.
   During this gap, the VM's user(s) will *see* a pause, so it is desirable to
   minimize this window.

3. Between the last time any page was copied from the source to the target, and
   when the VM was paused, the contents of that page may have changed - and
   therefore the copy we have on the target machine is out of date. Although we
   can keep track of which pages are out of date, for VMs with large amounts of
   memory, it is "slow" to transfer this information to the target machine. We
   want to resume execution before such a transfer would complete.

4. So, the guest begins executing on the target machine. The first time it
   touches its memory (via the UFFD-registered mapping), userspace wants to
   intercept this fault. Userspace checks whether or not the page is up to date,
   and if not, copies the updated page from the source machine, via the non-UFFD
   mapping. Finally, whether a copy was performed or not, userspace issues a
   UFFDIO_CONTINUE ioctl to tell the kernel "I have ensured the page contents
   are correct, carry on setting up the mapping".

We don't have to do all of the final updates on-demand. The userfaultfd manager
can, in the background, also copy over updated pages once it receives the map of
which pages are up-to-date or not.

Interaction with Existing APIs
==============================

Because this is a feature, a registered VMA could potentially receive both
missing and minor faults.  I spent some time thinking through how the
existing API interacts with the new feature:

UFFDIO_CONTINUE cannot be used to resolve non-minor faults, as it does not
allocate a new page.  If UFFDIO_CONTINUE is used on a non-minor fault:

- For non-shared memory or shmem, -EINVAL is returned.
- For hugetlb, -EFAULT is returned.

UFFDIO_COPY and UFFDIO_ZEROPAGE cannot be used to resolve minor faults.
Without modifications, the existing codepath assumes a new page needs to
be allocated.  This is okay, since userspace must have a second
non-UFFD-registered mapping anyway, thus there isn't much reason to want
to use these in any case (just memcpy or memset or similar).

- If UFFDIO_COPY is used on a minor fault, -EEXIST is returned.
- If UFFDIO_ZEROPAGE is used on a minor fault, -EEXIST is returned (or -EINVAL
  in the case of hugetlb, as UFFDIO_ZEROPAGE is unsupported in any case).
- UFFDIO_WRITEPROTECT simply doesn't work with shared memory, and returns
  -ENOENT in that case (regardless of the kind of fault).

Future Work
===========

This series only supports hugetlbfs.  I have a second series in flight to
support shmem as well, extending the functionality.  This series is more
mature than the shmem support at this point, and the functionality works
fully on hugetlbfs, so this series can be merged first and then shmem
support will follow.

This patch (of 6):

This feature allows userspace to intercept "minor" faults.  By "minor"
faults, I mean the following situation:

Let there exist two mappings (i.e., VMAs) to the same page(s).  One of the
mappings is registered with userfaultfd (in minor mode), and the other is
not.  Via the non-UFFD mapping, the underlying pages have already been
allocated &amp; filled with some contents.  The UFFD mapping has not yet been
faulted in; when it is touched for the first time, this results in what
I'm calling a "minor" fault.  As a concrete example, when working with
hugetlbfs, we have huge_pte_none(), but find_lock_page() finds an existing
page.

This commit adds the new registration mode, and sets the relevant flag on
the VMAs being registered.  In the hugetlb fault path, if we find that we
have huge_pte_none(), but find_lock_page() does indeed find an existing
page, then we have a "minor" fault, and if the VMA has the userfaultfd
registration flag, we call into userfaultfd to handle it.

This is implemented as a new registration mode, instead of an API feature.
This is because the alternative implementation has significant drawbacks
[1].

However, doing it this was requires we allocate a VM_* flag for the new
registration mode.  On 32-bit systems, there are no unused bits, so this
feature is only supported on architectures with
CONFIG_ARCH_USES_HIGH_VMA_FLAGS.  When attempting to register a VMA in
MINOR mode on 32-bit architectures, we return -EINVAL.

[1] https://lore.kernel.org/patchwork/patch/1380226/

[peterx@redhat.com: fix minor fault page leak]
  Link: https://lkml.kernel.org/r/20210322175132.36659-1-peterx@redhat.com

Link: https://lkml.kernel.org/r/20210301222728.176417-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20210301222728.176417-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen &lt;axelrasmussen@google.com&gt;
Reviewed-by: Peter Xu &lt;peterx@redhat.com&gt;
Reviewed-by: Mike Kravetz &lt;mike.kravetz@oracle.com&gt;
Cc: Alexander Viro &lt;viro@zeniv.linux.org.uk&gt;
Cc: Alexey Dobriyan &lt;adobriyan@gmail.com&gt;
Cc: Andrea Arcangeli &lt;aarcange@redhat.com&gt;
Cc: Anshuman Khandual &lt;anshuman.khandual@arm.com&gt;
Cc: Catalin Marinas &lt;catalin.marinas@arm.com&gt;
Cc: Chinwen Chang &lt;chinwen.chang@mediatek.com&gt;
Cc: Huang Ying &lt;ying.huang@intel.com&gt;
Cc: Ingo Molnar &lt;mingo@redhat.com&gt;
Cc: Jann Horn &lt;jannh@google.com&gt;
Cc: Jerome Glisse &lt;jglisse@redhat.com&gt;
Cc: Lokesh Gidra &lt;lokeshgidra@google.com&gt;
Cc: "Matthew Wilcox (Oracle)" &lt;willy@infradead.org&gt;
Cc: Michael Ellerman &lt;mpe@ellerman.id.au&gt;
Cc: "Michal Koutn" &lt;mkoutny@suse.com&gt;
Cc: Michel Lespinasse &lt;walken@google.com&gt;
Cc: Mike Rapoport &lt;rppt@linux.vnet.ibm.com&gt;
Cc: Nicholas Piggin &lt;npiggin@gmail.com&gt;
Cc: Peter Xu &lt;peterx@redhat.com&gt;
Cc: Shaohua Li &lt;shli@fb.com&gt;
Cc: Shawn Anastasio &lt;shawn@anastas.io&gt;
Cc: Steven Rostedt &lt;rostedt@goodmis.org&gt;
Cc: Steven Price &lt;steven.price@arm.com&gt;
Cc: Vlastimil Babka &lt;vbabka@suse.cz&gt;
Cc: Adam Ruprecht &lt;ruprecht@google.com&gt;
Cc: Axel Rasmussen &lt;axelrasmussen@google.com&gt;
Cc: Cannon Matthews &lt;cannonmatthews@google.com&gt;
Cc: "Dr . David Alan Gilbert" &lt;dgilbert@redhat.com&gt;
Cc: David Rientjes &lt;rientjes@google.com&gt;
Cc: Mina Almasry &lt;almasrymina@google.com&gt;
Cc: Oliver Upton &lt;oupton@google.com&gt;
Cc: Kirill A. Shutemov &lt;kirill@shutemov.name&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
</entry>
</feed>
