7 files changed, 343 insertions, 8 deletions
diff --git a/Documentation/admin-guide/device-mapper/dm-crypt.rst b/Documentation/admin-guide/device-mapper/dm-crypt.rst
index 9f8139ff97d6..4467f6d4b632 100644
--- a/Documentation/admin-guide/device-mapper/dm-crypt.rst
+++ b/Documentation/admin-guide/device-mapper/dm-crypt.rst
@@ -146,6 +146,11 @@ integrity:<bytes>:<type>
     integrity for the encrypted device. The additional space is then
     used for storing authentication tag (and persistent IV if needed).
 
+integrity_key_size:<bytes>
+    Optionally set the integrity key size if it differs from the digest size.
+    It allows the use of wrapped key algorithms where the key size is
+    independent of the cryptographic key size.
+
 sector_size:<bytes>
     Use <bytes> as the encryption unit instead of 512 bytes sectors.
     This option can be in range 512 - 4096 bytes and must be power of two.
diff --git a/Documentation/admin-guide/device-mapper/dm-integrity.rst b/Documentation/admin-guide/device-mapper/dm-integrity.rst
index d8a5f14d0e3c..c2e18ecc065c 100644
--- a/Documentation/admin-guide/device-mapper/dm-integrity.rst
+++ b/Documentation/admin-guide/device-mapper/dm-integrity.rst
@@ -92,6 +92,11 @@ Target arguments:
 		allowed. This mode is useful for data recovery if the
 		device cannot be activated in any of the other standard
 		modes.
+	I - inline mode - in this mode, dm-integrity will store integrity
+		data directly in the underlying device sectors.
+		The underlying device must have an integrity profile that
+		allows storing user integrity data and provides enough
+		space for the selected integrity tag.
 
 5. the number of additional arguments
 
diff --git a/Documentation/admin-guide/device-mapper/verity.rst b/Documentation/admin-guide/device-mapper/verity.rst
index a65c1602cb23..8c3f1f967a3c 100644
--- a/Documentation/admin-guide/device-mapper/verity.rst
+++ b/Documentation/admin-guide/device-mapper/verity.rst
@@ -87,6 +87,15 @@ panic_on_corruption
     Panic the device when a corrupted block is discovered. This option is
     not compatible with ignore_corruption and restart_on_corruption.
 
+restart_on_error
+    Restart the system when an I/O error is detected.
+    This option can be combined with the restart_on_corruption option.
+
+panic_on_error
+    Panic the device when an I/O error is detected. This option is
+    not compatible with the restart_on_error option but can be combined
+    with the panic_on_corruption option.
+
 ignore_zero_blocks
     Do not verify blocks that are expected to contain zeroes and always return
     zeroes instead. This may be useful if the partition contains unused blocks
@@ -142,8 +151,15 @@ root_hash_sig_key_desc <key_description>
     already in the secondary trusted keyring.
 
 try_verify_in_tasklet
-    If verity hashes are in cache, verify data blocks in kernel tasklet instead
-    of workqueue. This option can reduce IO latency.
+    If verity hashes are in cache and the IO size does not exceed the limit,
+    verify data blocks in bottom half instead of workqueue. This option can
+    reduce IO latency. The size limits can be configured via
+    /sys/module/dm_verity/parameters/use_bh_bytes. The four parameters
+    correspond to limits for IOPRIO_CLASS_NONE, IOPRIO_CLASS_RT,
+    IOPRIO_CLASS_BE and IOPRIO_CLASS_IDLE in turn.
+    For example:
+    <none>,<rt>,<be>,<idle>
+    4096,4096,4096,4096
 
 Theory of operation
 ===================
diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst
index ff0b440ef2dc..451874b8135d 100644
--- a/Documentation/admin-guide/hw-vuln/index.rst
+++ b/Documentation/admin-guide/hw-vuln/index.rst
@@ -22,3 +22,4 @@ are configurable at compile, boot or run time.
    srso
    gather_data_sampling
    reg-file-data-sampling
+   rsb
diff --git a/Documentation/admin-guide/hw-vuln/rsb.rst b/Documentation/admin-guide/hw-vuln/rsb.rst
new file mode 100644
index 000000000000..21dbf9cf25f8
--- /dev/null
+++ b/Documentation/admin-guide/hw-vuln/rsb.rst
@@ -0,0 +1,268 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+RSB-related mitigations
+=======================
+
+.. warning::
+   Please keep this document up-to-date, otherwise you will be
+   volunteered to update it and convert it to a very long comment in
+   bugs.c!
+
+Since 2018 there have been many Spectre CVEs related to the Return Stack
+Buffer (RSB) (sometimes referred to as the Return Address Stack (RAS) or
+Return Address Predictor (RAP) on AMD).
+
+Information about these CVEs and how to mitigate them is scattered
+amongst a myriad of microarchitecture-specific documents.
+
+This document attempts to consolidate all the relevant information in
+once place and clarify the reasoning behind the current RSB-related
+mitigations.  It's meant to be as concise as possible, focused only on
+the current kernel mitigations: what are the RSB-related attack vectors
+and how are they currently being mitigated?
+
+It's *not* meant to describe how the RSB mechanism operates or how the
+exploits work.  More details about those can be found in the references
+below.
+
+Rather, this is basically a glorified comment, but too long to actually
+be one.  So when the next CVE comes along, a kernel developer can
+quickly refer to this as a refresher to see what we're actually doing
+and why.
+
+At a high level, there are two classes of RSB attacks: RSB poisoning
+(Intel and AMD) and RSB underflow (Intel only).  They must each be
+considered individually for each attack vector (and microarchitecture
+where applicable).
+
+----
+
+RSB poisoning (Intel and AMD)
+=============================
+
+SpectreRSB
+~~~~~~~~~~
+
+RSB poisoning is a technique used by SpectreRSB [#spectre-rsb]_ where
+an attacker poisons an RSB entry to cause a victim's return instruction
+to speculate to an attacker-controlled address.  This can happen when
+there are unbalanced CALLs/RETs after a context switch or VMEXIT.
+
+* All attack vectors can potentially be mitigated by flushing out any
+  poisoned RSB entries using an RSB filling sequence
+  [#intel-rsb-filling]_ [#amd-rsb-filling]_ when transitioning between
+  untrusted and trusted domains.  But this has a performance impact and
+  should be avoided whenever possible.
+
+  .. DANGER::
+     **FIXME**: Currently we're flushing 32 entries.  However, some CPU
+     models have more than 32 entries.  The loop count needs to be
+     increased for those.  More detailed information is needed about RSB
+     sizes.
+
+* On context switch, the user->user mitigation requires ensuring the
+  RSB gets filled or cleared whenever IBPB gets written [#cond-ibpb]_
+  during a context switch:
+
+  * AMD:
+	On Zen 4+, IBPB (or SBPB [#amd-sbpb]_ if used) clears the RSB.
+	This is indicated by IBPB_RET in CPUID [#amd-ibpb-rsb]_.
+
+	On Zen < 4, the RSB filling sequence [#amd-rsb-filling]_ must be
+	always be done in addition to IBPB [#amd-ibpb-no-rsb]_.  This is
+	indicated by X86_BUG_IBPB_NO_RET.
+
+  * Intel:
+	IBPB always clears the RSB:
+
+	"Software that executed before the IBPB command cannot control
+	the predicted targets of indirect branches executed after the
+	command on the same logical processor. The term indirect branch
+	in this context includes near return instructions, so these
+	predicted targets may come from the RSB." [#intel-ibpb-rsb]_
+
+* On context switch, user->kernel attacks are prevented by SMEP.  User
+  space can only insert user space addresses into the RSB.  Even
+  non-canonical addresses can't be inserted due to the page gap at the
+  end of the user canonical address space reserved by TASK_SIZE_MAX.
+  A SMEP #PF at instruction fetch prevents the kernel from speculatively
+  executing user space.
+
+  * AMD:
+	"Finally, branches that are predicted as 'ret' instructions get
+	their predicted targets from the Return Address Predictor (RAP).
+	AMD recommends software use a RAP stuffing sequence (mitigation
+	V2-3 in [2]) and/or Supervisor Mode Execution Protection (SMEP)
+	to ensure that the addresses in the RAP are safe for
+	speculation. Collectively, we refer to these mitigations as "RAP
+	Protection"." [#amd-smep-rsb]_
+
+  * Intel:
+	"On processors with enhanced IBRS, an RSB overwrite sequence may
+	not suffice to prevent the predicted target of a near return
+	from using an RSB entry created in a less privileged predictor
+	mode.  Software can prevent this by enabling SMEP (for
+	transitions from user mode to supervisor mode) and by having
+	IA32_SPEC_CTRL.IBRS set during VM exits." [#intel-smep-rsb]_
+
+* On VMEXIT, guest->host attacks are mitigated by eIBRS (and PBRSB
+  mitigation if needed):
+
+  * AMD:
+	"When Automatic IBRS is enabled, the internal return address
+	stack used for return address predictions is cleared on VMEXIT."
+	[#amd-eibrs-vmexit]_
+
+  * Intel:
+	"On processors with enhanced IBRS, an RSB overwrite sequence may
+	not suffice to prevent the predicted target of a near return
+	from using an RSB entry created in a less privileged predictor
+	mode.  Software can prevent this by enabling SMEP (for
+	transitions from user mode to supervisor mode) and by having
+	IA32_SPEC_CTRL.IBRS set during VM exits. Processors with
+	enhanced IBRS still support the usage model where IBRS is set
+	only in the OS/VMM for OSes that enable SMEP. To do this, such
+	processors will ensure that guest behavior cannot control the
+	RSB after a VM exit once IBRS is set, even if IBRS was not set
+	at the time of the VM exit." [#intel-eibrs-vmexit]_
+
+    Note that some Intel CPUs are susceptible to Post-barrier Return
+    Stack Buffer Predictions (PBRSB) [#intel-pbrsb]_, where the last
+    CALL from the guest can be used to predict the first unbalanced RET.
+    In this case the PBRSB mitigation is needed in addition to eIBRS.
+
+AMD RETBleed / SRSO / Branch Type Confusion
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+On AMD, poisoned RSB entries can also be created by the AMD RETBleed
+variant [#retbleed-paper]_ [#amd-btc]_ or by Speculative Return Stack
+Overflow [#amd-srso]_ (Inception [#inception-paper]_).  The kernel
+protects itself by replacing every RET in the kernel with a branch to a
+single safe RET.
+
+----
+
+RSB underflow (Intel only)
+==========================
+
+RSB Alternate (RSBA) ("Intel Retbleed")
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some Intel Skylake-generation CPUs are susceptible to the Intel variant
+of RETBleed [#retbleed-paper]_ (Return Stack Buffer Underflow
+[#intel-rsbu]_).  If a RET is executed when the RSB buffer is empty due
+to mismatched CALLs/RETs or returning from a deep call stack, the branch
+predictor can fall back to using the Branch Target Buffer (BTB).  If a
+user forces a BTB collision then the RET can speculatively branch to a
+user-controlled address.
+
+* Note that RSB filling doesn't fully mitigate this issue.  If there
+  are enough unbalanced RETs, the RSB may still underflow and fall back
+  to using a poisoned BTB entry.
+
+* On context switch, user->user underflow attacks are mitigated by the
+  conditional IBPB [#cond-ibpb]_ on context switch which effectively
+  clears the BTB:
+
+  * "The indirect branch predictor barrier (IBPB) is an indirect branch
+    control mechanism that establishes a barrier, preventing software
+    that executed before the barrier from controlling the predicted
+    targets of indirect branches executed after the barrier on the same
+    logical processor." [#intel-ibpb-btb]_
+
+* On context switch and VMEXIT, user->kernel and guest->host RSB
+  underflows are mitigated by IBRS or eIBRS:
+
+  * "Enabling IBRS (including enhanced IBRS) will mitigate the "RSBU"
+    attack demonstrated by the researchers. As previously documented,
+    Intel recommends the use of enhanced IBRS, where supported. This
+    includes any processor that enumerates RRSBA but not RRSBA_DIS_S."
+    [#intel-rsbu]_
+
+  However, note that eIBRS and IBRS do not mitigate intra-mode attacks.
+  Like RRSBA below, this is mitigated by clearing the BHB on kernel
+  entry.
+
+  As an alternative to classic IBRS, call depth tracking (combined with
+  retpolines) can be used to track kernel returns and fill the RSB when
+  it gets close to being empty.
+
+Restricted RSB Alternate (RRSBA)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Some newer Intel CPUs have Restricted RSB Alternate (RRSBA) behavior,
+which, similar to RSBA described above, also falls back to using the BTB
+on RSB underflow.  The only difference is that the predicted targets are
+restricted to the current domain when eIBRS is enabled:
+
+* "Restricted RSB Alternate (RRSBA) behavior allows alternate branch
+  predictors to be used by near RET instructions when the RSB is
+  empty.  When eIBRS is enabled, the predicted targets of these
+  alternate predictors are restricted to those belonging to the
+  indirect branch predictor entries of the current prediction domain.
+  [#intel-eibrs-rrsba]_
+
+When a CPU with RRSBA is vulnerable to Branch History Injection
+[#bhi-paper]_ [#intel-bhi]_, an RSB underflow could be used for an
+intra-mode BTI attack.  This is mitigated by clearing the BHB on
+kernel entry.
+
+However if the kernel uses retpolines instead of eIBRS, it needs to
+disable RRSBA:
+
+* "Where software is using retpoline as a mitigation for BHI or
+  intra-mode BTI, and the processor both enumerates RRSBA and
+  enumerates RRSBA_DIS controls, it should disable this behavior."
+  [#intel-retpoline-rrsba]_
+
+----
+
+References
+==========
+
+.. [#spectre-rsb] `Spectre Returns! Speculation Attacks using the Return Stack Buffer <https://arxiv.org/pdf/1807.07940.pdf>`_
+
+.. [#intel-rsb-filling] "Empty RSB Mitigation on Skylake-generation" in `Retpoline: A Branch Target Injection Mitigation <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/retpoline-branch-target-injection-mitigation.html#inpage-nav-5-1>`_
+
+.. [#amd-rsb-filling] "Mitigation V2-3" in `Software Techniques for Managing Speculation <https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/software-techniques-for-managing-speculation.pdf>`_
+
+.. [#cond-ibpb] Whether IBPB is written depends on whether the prev and/or next task is protected from Spectre attacks.  It typically requires opting in per task or system-wide.  For more details see the documentation for the ``spectre_v2_user`` cmdline option in Documentation/admin-guide/kernel-parameters.txt.
+
+.. [#amd-sbpb] IBPB without flushing of branch type predictions.  Only exists for AMD.
+
+.. [#amd-ibpb-rsb] "Function 8000_0008h -- Processor Capacity Parameters and Extended Feature Identification" in `AMD64 Architecture Programmer's Manual Volume 3: General-Purpose and System Instructions <https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24594.pdf>`_.  SBPB behaves the same way according to `this email <https://lore.kernel.org/5175b163a3736ca5fd01cedf406735636c99a>`_.
+
+.. [#amd-ibpb-no-rsb] `Spectre Attacks: Exploiting Speculative Execution <https://comsec.ethz.ch/wp-content/files/ibpb_sp25.pdf>`_
+
+.. [#intel-ibpb-rsb] "Introduction" in `Post-barrier Return Stack Buffer Predictions / CVE-2022-26373 / INTEL-SA-00706 <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/post-barrier-return-stack-buffer-predictions.html>`_
+
+.. [#amd-smep-rsb] "Existing Mitigations" in `Technical Guidance for Mitigating Branch Type Confusion <https://www.amd.com/content/dam/amd/en/documents/resources/technical-guidance-for-mitigating-branch-type-confusion.pdf>`_
+
+.. [#intel-smep-rsb] "Enhanced IBRS" in `Indirect Branch Restricted Speculation <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/indirect-branch-restricted-speculation.html>`_
+
+.. [#amd-eibrs-vmexit] "Extended Feature Enable Register (EFER)" in `AMD64 Architecture Programmer's Manual Volume 2: System Programming <https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf>`_
+
+.. [#intel-eibrs-vmexit] "Enhanced IBRS" in `Indirect Branch Restricted Speculation <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/indirect-branch-restricted-speculation.html>`_
+
+.. [#intel-pbrsb] `Post-barrier Return Stack Buffer Predictions / CVE-2022-26373 / INTEL-SA-00706 <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/post-barrier-return-stack-buffer-predictions.html>`_
+
+.. [#retbleed-paper] `RETBleed: Arbitrary Speculative Code Execution with Return Instruction <https://comsec.ethz.ch/wp-content/files/retbleed_sec22.pdf>`_
+
+.. [#amd-btc] `Technical Guidance for Mitigating Branch Type Confusion <https://www.amd.com/content/dam/amd/en/documents/resources/technical-guidance-for-mitigating-branch-type-confusion.pdf>`_
+
+.. [#amd-srso] `Technical Update Regarding Speculative Return Stack Overflow <https://www.amd.com/content/dam/amd/en/documents/corporate/cr/speculative-return-stack-overflow-whitepaper.pdf>`_
+
+.. [#inception-paper] `Inception: Exposing New Attack Surfaces with Training in Transient Execution <https://comsec.ethz.ch/wp-content/files/inception_sec23.pdf>`_
+
+.. [#intel-rsbu] `Return Stack Buffer Underflow / Return Stack Buffer Underflow / CVE-2022-29901, CVE-2022-28693 / INTEL-SA-00702 <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/return-stack-buffer-underflow.html>`_
+
+.. [#intel-ibpb-btb] `Indirect Branch Predictor Barrier' <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/indirect-branch-predictor-barrier.html>`_
+
+.. [#intel-eibrs-rrsba] "Guidance for RSBU" in `Return Stack Buffer Underflow / Return Stack Buffer Underflow / CVE-2022-29901, CVE-2022-28693 / INTEL-SA-00702 <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/return-stack-buffer-underflow.html>`_
+
+.. [#bhi-paper] `Branch History Injection: On the Effectiveness of Hardware Mitigations Against Cross-Privilege Spectre-v2 Attacks <http://download.vusec.net/papers/bhi-spectre-bhb_sec22.pdf>`_
+
+.. [#intel-bhi] `Branch History Injection and Intra-mode Branch Target Injection / CVE-2022-0001, CVE-2022-0002 / INTEL-SA-00598 <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/branch-history-injection.html>`_
+
+.. [#intel-retpoline-rrsba] "Retpoline" in `Branch History Injection and Intra-mode Branch Target Injection / CVE-2022-0001, CVE-2022-0002 / INTEL-SA-00598 <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/branch-history-injection.html>`_
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3f35d5b8c296..d9fd26b95b34 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1407,18 +1407,15 @@
 			earlyprintk=serial[,0x...[,baudrate]]
 			earlyprintk=ttySn[,baudrate]
 			earlyprintk=dbgp[debugController#]
+			earlyprintk=mmio32,membase[,{nocfg|baudrate}]
 			earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}]
 			earlyprintk=xdbc[xhciController#]
 			earlyprintk=bios
-			earlyprintk=mmio,membase[,{nocfg|baudrate}]
 
 			earlyprintk is useful when the kernel crashes before
 			the normal console is initialized. It is not enabled by
 			default because it has some cosmetic problems.
 
-			Only 32-bit memory addresses are supported for "mmio"
-			and "pciserial" devices.
-
 			Use "nocfg" to skip UART configuration, assume
 			BIOS/firmware has configured UART correctly.
 
@@ -4265,10 +4262,10 @@
 	nosmp		[SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
 			and disable the IO APIC.  legacy for "maxcpus=0".
 
-	nosmt		[KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
+	nosmt		[KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT).
 			Equivalent to smt=1.
 
-			[KNL,X86,PPC] Disable symmetric multithreading (SMT).
+			[KNL,X86,PPC,S390] Disable symmetric multithreading (SMT).
 			nosmt=force: Force disable SMT, cannot be undone
 				     via the sysfs control file.
 
@@ -7288,6 +7285,8 @@
 			This is just one of many ways that can clear memory. Make sure your system
 			keeps the content of memory across reboots before relying on this option.
 
+			NB: Both the mapped address and size must be page aligned for the architecture.
+
 			See also Documentation/trace/debugging.rst
 
 
@@ -7533,6 +7532,22 @@
 			Note that genuine overcurrent events won't be
 			reported either.
 
+	unaligned_scalar_speed=
+			[RISCV]
+			Format: {slow | fast | unsupported}
+			Allow skipping scalar unaligned access speed tests. This
+			is useful for testing alternative code paths and to skip
+			the tests in environments where they run too slowly. All
+			CPUs must have the same scalar unaligned access speed.
+
+	unaligned_vector_speed=
+			[RISCV]
+			Format: {slow | fast | unsupported}
+			Allow skipping vector unaligned access speed tests. This
+			is useful for testing alternative code paths and to skip
+			the tests in environments where they run too slowly. All
+			CPUs must have the same vector unaligned access speed.
+
 	unknown_nmi_panic
 			[X86] Cause panic on unknown NMI.
 
diff --git a/Documentation/admin-guide/sysctl/fs.rst b/Documentation/admin-guide/sysctl/fs.rst
index 08e89e031714..6c54718c9d04 100644
--- a/Documentation/admin-guide/sysctl/fs.rst
+++ b/Documentation/admin-guide/sysctl/fs.rst
@@ -347,3 +347,28 @@ filesystems:
 ``/proc/sys/fs/fuse/max_pages_limit`` is a read/write file for
 setting/getting the maximum number of pages that can be used for servicing
 requests in FUSE.
+
+``/proc/sys/fs/fuse/default_request_timeout`` is a read/write file for
+setting/getting the default timeout (in seconds) for a fuse server to
+reply to a kernel-issued request in the event where the server did not
+specify a timeout at mount. If the server set a timeout,
+then default_request_timeout will be ignored.  The default
+"default_request_timeout" is set to 0. 0 indicates no default timeout.
+The maximum value that can be set is 65535.
+
+``/proc/sys/fs/fuse/max_request_timeout`` is a read/write file for
+setting/getting the maximum timeout (in seconds) for a fuse server to
+reply to a kernel-issued request. A value greater than 0 automatically opts
+the server into a timeout that will be set to at most "max_request_timeout",
+even if the server did not specify a timeout and default_request_timeout is
+set to 0. If max_request_timeout is greater than 0 and the server set a timeout
+greater than max_request_timeout or default_request_timeout is set to a value
+greater than max_request_timeout, the system will use max_request_timeout as the
+timeout. 0 indicates no max request timeout. The maximum value that can be set
+is 65535.
+
+For timeouts, if the server does not respond to the request by the time
+the set timeout elapses, then the connection to the fuse server will be aborted.
+Please note that the timeouts are not 100% precise (eg you may set 60 seconds but
+the timeout may kick in after 70 seconds). The upper margin of error for the
+timeout is roughly FUSE_TIMEOUT_TIMER_FREQ seconds.