lwn.git/arch/x86/include/asm/pgtable.h, branch v3.14.48

Revert "xen: properly account for _PAGE_NUMA during xen pte translations"

2014-03-25T11:11:42+00:00

This reverts commit a9c8e4beeeb64c22b84c803747487857fe424b68. PTEs in Xen PV guests must contain machine addresses if _PAGE_PRESENT is set and pseudo-physical addresses is _PAGE_PRESENT is clear. This is because during a domain save/restore (migration) the page table entries are "canonicalised" and uncanonicalised". i.e., MFNs are converted to PFNs during domain save so that on a restore the page table entries may be rewritten with the new MFNs on the destination. This canonicalisation is only done for PTEs that are present. This change resulted in writing PTEs with MFNs if _PAGE_PROTNONE (or _PAGE_NUMA) was set but _PAGE_PRESENT was clear. These PTEs would be migrated as-is which would result in unexpected behaviour in the destination domain. Either a) the MFN would be translated to the wrong PFN/page; b) setting the _PAGE_PRESENT bit would clear the PTE because the MFN is no longer owned by the domain; or c) the present bit would not get set. Symptoms include "Bad page" reports when munmapping after migrating a domain. Signed-off-by: David Vrabel Acked-by: Konrad Rzeszutek Wilk Cc: [3.12+]

xen: properly account for _PAGE_NUMA during xen pte translations

2014-02-11T00:01:41+00:00

Steven Noonan forwarded a users report where they had a problem starting vsftpd on a Xen paravirtualized guest, with this in dmesg: BUG: Bad page map in process vsftpd pte:8000000493b88165 pmd:e9cc01067 page:ffffea00124ee200 count:0 mapcount:-1 mapping: (null) index:0x0 page flags: 0x2ffc0000000014(referenced|dirty) addr:00007f97eea74000 vm_flags:00100071 anon_vma:ffff880e98f80380 mapping: (null) index:7f97eea74 CPU: 4 PID: 587 Comm: vsftpd Not tainted 3.12.7-1-ec2 #1 Call Trace: dump_stack+0x45/0x56 print_bad_pte+0x22e/0x250 unmap_single_vma+0x583/0x890 unmap_vmas+0x65/0x90 exit_mmap+0xc5/0x170 mmput+0x65/0x100 do_exit+0x393/0x9e0 do_group_exit+0xcc/0x140 SyS_exit_group+0x14/0x20 system_call_fastpath+0x1a/0x1f Disabling lock debugging due to kernel taint BUG: Bad rss-counter state mm:ffff880e9ca60580 idx:0 val:-1 BUG: Bad rss-counter state mm:ffff880e9ca60580 idx:1 val:1 The issue could not be reproduced under an HVM instance with the same kernel, so it appears to be exclusive to paravirtual Xen guests. He bisected the problem to commit 1667918b6483 ("mm: numa: clear numa hinting information on mprotect") that was also included in 3.12-stable. The problem was related to how xen translates ptes because it was not accounting for the _PAGE_NUMA bit. This patch splits pte_present to add a pteval_present helper for use by xen so both bare metal and xen use the same code when checking if a PTE is present. [mgorman@suse.de: wrote changelog, proposed minor modifications] [akpm@linux-foundation.org: fix typo in comment] Reported-by: Steven Noonan Tested-by: Steven Noonan Signed-off-by: Elena Ufimtseva Signed-off-by: Mel Gorman Reviewed-by: David Vrabel Acked-by: Konrad Rzeszutek Wilk Cc: [3.12+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: fix TLB flush race between migration, and change_protection_range

2013-12-19T03:04:51+00:00

There are a few subtle races, between change_protection_range (used by mprotect and change_prot_numa) on one side, and NUMA page migration and compaction on the other side. The basic race is that there is a time window between when the PTE gets made non-present (PROT_NONE or NUMA), and the TLB is flushed. During that time, a CPU may continue writing to the page. This is fine most of the time, however compaction or the NUMA migration code may come in, and migrate the page away. When that happens, the CPU may continue writing, through the cached translation, to what is no longer the current memory location of the process. This only affects x86, which has a somewhat optimistic pte_accessible. All other architectures appear to be safe, and will either always flush, or flush whenever there is a valid mapping, even with no permissions (SPARC). The basic race looks like this: CPU A CPU B CPU C load TLB entry make entry PTE/PMD_NUMA fault on entry read/write old page start migrating page change PTE/PMD to new page read/write old page [*] flush TLB reload TLB from new entry read/write new page lose data [*] the old page may belong to a new user at this point! The obvious fix is to flush remote TLB entries, by making sure that pte_accessible aware of the fact that PROT_NONE and PROT_NUMA memory may still be accessible if there is a TLB flush pending for the mm. This should fix both NUMA migration and compaction. [mgorman@suse.de: fix build] Signed-off-by: Rik van Riel Signed-off-by: Mel Gorman Cc: Alex Thorlton Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: make sure _PAGE_SWP_SOFT_DIRTY bit is not set on present pte

2013-09-11T22:58:06+00:00

_PAGE_SOFT_DIRTY bit should never be set on present pte so add VM_BUG_ON to catch any potential future abuse. Also add a comment on _PAGE_SWP_SOFT_DIRTY definition explaining scope of its usage. Signed-off-by: Cyrill Gorcunov Acked-by: Pavel Emelyanov Acked-by: Jan Beulich Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'x86-asmlinkage-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2013-09-04T15:42:44+00:00

Pull x86/asmlinkage changes from Ingo Molnar: "As a preparation for Andi Kleen's LTO patchset (link time optimizations using GCC's -flto which build time optimization has steadily increased in quality over the past few years and might eventually be usable for the kernel too) this tree includes a handful of preparatory patches that make function calling convention annotations consistent again: - Mark every function without arguments (or 64bit only) that is used by assembly code with asmlinkage() - Mark every function with parameters or variables that is used by assembly code as __visible. For the vanilla kernel this has documentation, consistency and debuggability advantages, for the time being" * 'x86-asmlinkage-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/asmlinkage: Fix warning in xen asmlinkage change x86, asmlinkage, vdso: Mark vdso variables __visible x86, asmlinkage, power: Make various symbols used by the suspend asm code visible x86, asmlinkage: Make dump_stack visible x86, asmlinkage: Make 64bit checksum functions visible x86, asmlinkage, paravirt: Add __visible/asmlinkage to xen paravirt ops x86, asmlinkage, apm: Make APM data structure used from assembler visible x86, asmlinkage: Make syscall tables visible x86, asmlinkage: Make several variables used from assembler/linker script visible x86, asmlinkage: Make kprobes code visible and fix assembler code x86, asmlinkage: Make various syscalls asmlinkage x86, asmlinkage: Make 32bit/64bit __switch_to visible x86, asmlinkage: Make _*_start_kernel visible x86, asmlinkage: Make all interrupt handlers asmlinkage / __visible x86, asmlinkage: Change dotraplinkage into __visible on 32bit x86: Fix sys_call_table type in asm/syscall.h

mm: save soft-dirty bits on file pages

2013-08-14T00:57:48+00:00

Andy reported that if file page get reclaimed we lose the soft-dirty bit if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address get encoded into pte entry. Thus when #pf happens on such non-present pte we can restore it back. Reported-by: Andy Lutomirski Signed-off-by: Cyrill Gorcunov Acked-by: Pavel Emelyanov Cc: Matt Mackall Cc: Xiao Guangrong Cc: Marcelo Tosatti Cc: KOSAKI Motohiro Cc: Stephen Rothwell Cc: Peter Zijlstra Cc: "Aneesh Kumar K.V" Cc: Minchan Kim Cc: Wanpeng Li Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: save soft-dirty bits on swapped pages

2013-08-14T00:57:47+00:00

Andy Lutomirski reported that if a page with _PAGE_SOFT_DIRTY bit set get swapped out, the bit is getting lost and no longer available when pte read back. To resolve this we introduce _PTE_SWP_SOFT_DIRTY bit which is saved in pte entry for the page being swapped out. When such page is to be read back from a swap cache we check for bit presence and if it's there we clear it and restore the former _PAGE_SOFT_DIRTY bit back. One of the problem was to find a place in pte entry where we can save the _PTE_SWP_SOFT_DIRTY bit while page is in swap. The _PAGE_PSE was chosen for that, it doesn't intersect with swap entry format stored in pte. Reported-by: Andy Lutomirski Signed-off-by: Cyrill Gorcunov Acked-by: Pavel Emelyanov Cc: Matt Mackall Cc: Xiao Guangrong Cc: Marcelo Tosatti Cc: KOSAKI Motohiro Cc: Stephen Rothwell Cc: Peter Zijlstra Cc: "Aneesh Kumar K.V" Reviewed-by: Minchan Kim Reviewed-by: Wanpeng Li Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

x86, asmlinkage: Make several variables used from assembler/linker script visible

2013-08-06T21:20:13+00:00

Plus one function, load_gs_index(). Signed-off-by: Andi Kleen Link: http://lkml.kernel.org/r/1375740170-7446-10-git-send-email-andi@firstfloor.org Signed-off-by: H. Peter Anvin

mm: soft-dirty bits for user memory changes tracking

2013-07-03T23:07:26+00:00

The soft-dirty is a bit on a PTE which helps to track which pages a task writes to. In order to do this tracking one should 1. Clear soft-dirty bits from PTEs ("echo 4 > /proc/PID/clear_refs) 2. Wait some time. 3. Read soft-dirty bits (55'th in /proc/PID/pagemap2 entries) To do this tracking, the writable bit is cleared from PTEs when the soft-dirty bit is. Thus, after this, when the task tries to modify a page at some virtual address the #PF occurs and the kernel sets the soft-dirty bit on the respective PTE. Note, that although all the task's address space is marked as r/o after the soft-dirty bits clear, the #PF-s that occur after that are processed fast. This is so, since the pages are still mapped to physical memory, and thus all the kernel does is finds this fact out and puts back writable, dirty and soft-dirty bits on the PTE. Another thing to note, is that when mremap moves PTEs they are marked with soft-dirty as well, since from the user perspective mremap modifies the virtual memory at mremap's new address. Signed-off-by: Pavel Emelyanov Cc: Matt Mackall Cc: Xiao Guangrong Cc: Glauber Costa Cc: Marcelo Tosatti Cc: KOSAKI Motohiro Cc: Stephen Rothwell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

consolidate io_remap_pfn_range definitions

2013-06-29T08:46:35+00:00

Signed-off-by: Al Viro