We want to limit the use of page_mapcount() to places where absolutely
required, to prepare for kernel configs where we won't keep track of
per-page mapcounts in large folios.
khugepaged is one of the remaining "more challenging" page_mapcount()
users, but we might be able to move away from page_mapcount() without
resulting in a significant behavior change that would warrant
special-casing based on kernel configs.
In 2020, we first added support to khugepaged for collapsing COW-shared
pages via commit 9445689f3b ("khugepaged: allow to collapse a page
shared across fork"), followed by support for collapsing PTE-mapped THP in
commit 5503fbf2b0 ("khugepaged: allow to collapse PTE-mapped compound
pages") and limiting the memory waste via the "page_count() > 1" check in
commit 71a2c112a0 ("khugepaged: introduce 'max_ptes_shared' tunable").
As a default, khugepaged will allow up to half of the PTEs to map shared
pages: where page_mapcount() > 1. MADV_COLLAPSE ignores the khugepaged
setting.
khugepaged does currently not care about swapcache page references, and
does not check under folio lock: so in some corner cases the "shared vs.
exclusive" detection might be a bit off, making us detect "exclusive" when
it's actually "shared".
Most of our anonymous folios in the system are usually exclusive. We
frequently see sharing of anonymous folios for a short period of time,
after which our short-lived suprocesses either quit or exec().
There are some famous examples, though, where child processes exist for a
long time, and where memory is COW-shared with a lot of processes
(webservers, webbrowsers, sshd, ...) and COW-sharing is crucial for
reducing the memory footprint. We don't want to suddenly change the
behavior to result in a significant increase in memory waste.
Interestingly, khugepaged will only collapse an anonymous THP if at least
one PTE is writable. After fork(), that means that something (usually a
page fault) populated at least a single exclusive anonymous THP in that
PMD range.
So ... what happens when we switch to "is this folio mapped shared"
instead of "is this page mapped shared" by using
folio_likely_mapped_shared()?
For "not-COW-shared" folios, small folios and for THPs (large folios) that
are completely mapped into at least one process, switching to
folio_likely_mapped_shared() will not result in a change.
We'll only see a change for COW-shared PTE-mapped THPs that are partially
mapped into all involved processes.
There are two cases to consider:
(A) folio_likely_mapped_shared() returns "false" for a PTE-mapped THP
If the folio is detected as exclusive, and it actually is exclusive,
there is no change: page_mapcount() == 1. This is the common case
without fork() or with short-lived child processes.
folio_likely_mapped_shared() might currently still detect a folio as
exclusive although it is shared (false negatives): if the first page is
not mapped multiple times and if the average per-page mapcount is smaller
than 1, implying that (1) the folio is partially mapped and (2) if we are
responsible for many mapcounts by mapping many pages others can't
("mostly exclusive") (3) if we are not responsible for many mapcounts by
mapping little pages ("mostly shared") it won't make a big impact on the
end result.
So while we might now detect a page as "exclusive" although it isn't,
it's not expected to make a big difference in common cases.
(B) folio_likely_mapped_shared() returns "true" for a PTE-mapped THP
folio_likely_mapped_shared() will never detect a large anonymous folio
as shared although it is exclusive: there are no false positives.
If we detect a THP as shared, at least one page of the THP is mapped by
another process. It could well be that some pages are actually exclusive.
For example, our child processes could have unmapped/COW'ed some pages
such that they would now be exclusive to out process, which we now
would treat as still-shared.
Examples:
(1) Parent maps all pages of a THP, child maps some pages. We detect
all pages in the parent as shared although some are actually
exclusive.
(2) Parent maps all but some page of a THP, child maps the remainder.
We detect all pages of the THP that the parent maps as shared
although they are all exclusive.
In (1) we wouldn't collapse a THP right now already: no PTE
is writable, because a write fault would have resulted in COW of a
single page and the parent would no longer map all pages of that THP.
For (2) we would have collapsed a THP in the parent so far, now we
wouldn't as long as the child process is still alive: unless the child
process unmaps the remaining THP pages or we decide to split that THP.
Possibly, the child COW'ed many pages, meaning that it's likely that
we can populate a THP for our child first, and then for our parent.
For (2), we are making really bad use of the THP in the first
place (not even mapped completely in at least one process). If the
THP would be completely partially mapped, it would be on the deferred
split queue where we would split it lazily later.
For short-running child processes, we don't particularly care. For
long-running processes, the expectation is that such scenarios are
rather rare: further, a THP might be best placed if most data in the
PMD range is actually written, implying that we'll have to COW more
pages first before khugepaged would collapse it.
To summarize, in the common case, this change is not expected to matter
much. The more common application of khugepaged operates on exclusive
pages, either before fork() or after a child quit.
Can we improve (A)? Yes, if we implement more precise tracking of "mapped
shared" vs. "mapped exclusively", we could get rid of the false negatives
completely.
Can we improve (B)? We could count how many pages of a large folio we map
inside the current page table and detect that we are responsible for most
of the folio mapcount and conclude "as good as exclusive", which might
help in some cases. ... but likely, some other mechanism should detect
that the THP is not a good use in the scenario (not even mapped completely
in a single process) and try splitting that folio lazily etc.
We'll move the folio_test_anon() check before our "shared" check, so we
might get more expressive results for SCAN_EXCEED_SHARED_PTE: this order
of checks now matches the one in __collapse_huge_page_isolate(). Extend
documentation.
Link: https://lkml.kernel.org/r/20240424122630.495788-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Previously we claimed "pcie_aspm=off" meant that ASPM would be disabled,
which is wrong.
Correct this to say that with "pcie_aspm=off", Linux doesn't touch any ASPM
configuration at all. ASPM may have been enabled by firmware, and that
will be left unchanged. See "aspm_support_enabled".
Link: https://lore.kernel.org/r/20240429191821.691726-1-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: David E. Box <david.e.box@linux.intel.com>
This document mainly describe the functionality of IPU6 and IPU6 isys
driver, and gives an example that how user can do imaging capture with
tools.
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Pull x86 fixes from Ingo Molnar:
- Make the CPU_MITIGATIONS=n interaction with conflicting
mitigation-enabling boot parameters a bit saner.
- Re-enable CPU mitigations by default on non-x86
- Fix TDX shared bit propagation on mprotect()
- Fix potential show_regs() system hang when PKE initialization
is not fully finished yet.
- Add the 0x10-0x1f model IDs to the Zen5 range
- Harden #VC instruction emulation some more
* tag 'x86-urgent-2024-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
cpu: Ignore "mitigations" kernel parameter if CPU_MITIGATIONS=n
cpu: Re-enable CPU mitigations by default for !X86 architectures
x86/tdx: Preserve shared bit on mprotect()
x86/cpu: Fix check for RDPKRU in __show_regs()
x86/CPU/AMD: Add models 0x10-0x1f to the Zen5 range
x86/sev: Check for MWAITX and MONITORX opcodes in the #VC handler
Implements the "init_mlocked_on_free" boot option. When this boot option
is enabled, any mlock'ed pages are zeroed on free. If
the pages are munlock'ed beforehand, no initialization takes place.
This boot option is meant to combat the performance hit of
"init_on_free" as reported in commit 6471384af2 ("mm: security:
introduce init_on_alloc=1 and init_on_free=1 boot options"). With
"init_mlocked_on_free=1" only relevant data is freed while everything
else is left untouched by the kernel. Correspondingly, this patch
introduces no performance hit for unmapping non-mlock'ed memory. The
unmapping overhead for purely mlocked memory was measured to be
approximately 13%. Realistically, most systems mlock only a fraction of
the total memory so the real-world system overhead should be close to
zero.
Optimally, userspace programs clear any key material or other
confidential memory before exit and munlock the according memory
regions. If a program crashes, userspace key managers fail to do this
job. Accordingly, no munlock operations are performed so the data is
caught and zeroed by the kernel. Should the program not crash, all
memory will ideally be munlocked so no overhead is caused.
CONFIG_INIT_MLOCKED_ON_FREE_DEFAULT_ON can be set to enable
"init_mlocked_on_free" by default.
Link: https://lkml.kernel.org/r/20240329145605.149917-1-yjnworkstation@gmail.com
Signed-off-by: York Jasper Niebuhr <yjnworkstation@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: York Jasper Niebuhr <yjnworkstation@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Explicitly disallow enabling mitigations at runtime for kernels that were
built with CONFIG_CPU_MITIGATIONS=n, as some architectures may omit code
entirely if mitigations are disabled at compile time.
E.g. on x86, a large pile of Kconfigs are buried behind CPU_MITIGATIONS,
and trying to provide sane behavior for retroactively enabling mitigations
is extremely difficult, bordering on impossible. E.g. page table isolation
and call depth tracking require build-time support, BHI mitigations will
still be off without additional kernel parameters, etc.
[ bp: Touchups. ]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240420000556.2645001-3-seanjc@google.com
Commit 839195352d ("mm/shuffle: remove dynamic reconfiguration")
removed the dynamic reconfiguration capabilities from the shuffle page
allocator. This means that, now, we don't have any perspective of an
"autodetection of memory-side-cache" that triggers the enablement of the
shuffle page allocator.
Therefore, let the documentation reflect that the only way to enable
the shuffle page allocator is by setting `page_alloc.shuffle=1`.
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240422142007.1062231-1-mcanal@igalia.com
We want the tty fixes in here as well, and it resolves a merge conflict
in:
drivers/tty/serial/serial_core.c
as well.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Pull documentation fixes from Jonathan Corbet:
"A set of updates from Thorsten to his (new) guide to verifying bugs
and tracking down regressions"
* tag 'docs-6.9-fixes2' of git://git.lwn.net/linux:
docs: verify/bisect: stable regressions: first stable, then mainline
docs: verify/bisect: describe how to use a build host
docs: verify/bisect: explain testing reverts, patches and newer code
docs: verify/bisect: proper headlines and more spacing
docs: verify/bisect: add and fetch stable branches ahead of time
docs: verify/bisect: use git switch, tag kernel, and various fixes
This patch add two entries (pids.peak and pids.events) for pids
controller, and also update pids.current because it's on non-root.
Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Since kernel virtual and physical address spaces are
uncoupled the kernel is mapped at the top of the virtual
address space in case KASLR is disabled.
That does not pose any issue with regard to the kernel
booting and operation, but makes it difficult to use a
generated vmlinux with some debugging tools (e.g. gdb),
because the exact location of the kernel image in virtual
memory is unknown. Make that location known and introduce
CONFIG_KERNEL_IMAGE_BASE configuration option.
A custom CONFIG_KERNEL_IMAGE_BASE value that would break
the virtual memory layout leads to a build error.
The kernel image size is defined by KERNEL_IMAGE_SIZE
macro and set to 512 MB, by analogy with x86.
Suggested-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
When WQ_HIGHPRI was used for the dm-crypt kcryptd workqueue it was
reported that dm-crypt performs badly when the system is loaded[1].
Because of reports of audio skipping, dm-crypt stopped using
WQ_HIGHPRI with commit f612b2132d (Revert "dm crypt: use WQ_HIGHPRI
for the IO and crypt workqueues").
But it has since been determined that WQ_HIGHPRI provides improved
performance (with reduced latency) for highend systems with much more
resources than those laptop/desktop users which suffered from the use
of WQ_HIGHPRI.
As such, add an option "high_priority" that allows the use of
WQ_HIGHPRI for dm-crypt's workqueues and also sets the write_thread to
nice level MIN_NICE (-20). This commit makes it optional, so that
normal users won't be harmed by it.
[1] https://listman.redhat.com/archives/dm-devel/2023-February/053410.html
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
A call to a synchronize_rcu() can be optimized from a latency
point of view. Workloads which depend on this can benefit of it.
The delay of wakeme_after_rcu() callback, which unblocks a waiter,
depends on several factors:
- how fast a process of offloading is started. Combination of:
- !CONFIG_RCU_NOCB_CPU/CONFIG_RCU_NOCB_CPU;
- !CONFIG_RCU_LAZY/CONFIG_RCU_LAZY;
- other.
- when started, invoking path is interrupted due to:
- time limit;
- need_resched();
- if limit is reached.
- where in a nocb list it is located;
- how fast previous callbacks completed;
Example:
1. On our embedded devices i can easily trigger the scenario when
it is a last in the list out of ~3600 callbacks:
<snip>
<...>-29 [001] d..1. 21950.145313: rcu_batch_start: rcu_preempt CBs=3613 bl=28
...
<...>-29 [001] ..... 21950.152578: rcu_invoke_callback: rcu_preempt rhp=00000000b2d6dee8 func=__free_vm_area_struct.cfi_jt
<...>-29 [001] ..... 21950.152579: rcu_invoke_callback: rcu_preempt rhp=00000000a446f607 func=__free_vm_area_struct.cfi_jt
<...>-29 [001] ..... 21950.152580: rcu_invoke_callback: rcu_preempt rhp=00000000a5cab03b func=__free_vm_area_struct.cfi_jt
<...>-29 [001] ..... 21950.152581: rcu_invoke_callback: rcu_preempt rhp=0000000013b7e5ee func=__free_vm_area_struct.cfi_jt
<...>-29 [001] ..... 21950.152582: rcu_invoke_callback: rcu_preempt rhp=000000000a8ca6f9 func=__free_vm_area_struct.cfi_jt
<...>-29 [001] ..... 21950.152583: rcu_invoke_callback: rcu_preempt rhp=000000008f162ca8 func=wakeme_after_rcu.cfi_jt
<...>-29 [001] d..1. 21950.152625: rcu_batch_end: rcu_preempt CBs-invoked=3612 idle=....
<snip>
2. We use cpuset/cgroup to classify tasks and assign them into
different cgroups. For example "backgrond" group which binds tasks
only to little CPUs or "foreground" which makes use of all CPUs.
Tasks can be migrated between groups by a request if an acceleration
is needed.
See below an example how "surfaceflinger" task gets migrated.
Initially it is located in the "system-background" cgroup which
allows to run only on little cores. In order to speed it up it
can be temporary moved into "foreground" cgroup which allows
to use big/all CPUs:
cgroup_attach_task():
-> cgroup_migrate_execute()
-> cpuset_can_attach()
-> percpu_down_write()
-> rcu_sync_enter()
-> synchronize_rcu()
-> now move tasks to the new cgroup.
-> cgroup_migrate_finish()
<snip>
rcuop/1-29 [000] ..... 7030.528570: rcu_invoke_callback: rcu_preempt rhp=00000000461605e0 func=wakeme_after_rcu.cfi_jt
PERFD-SERVER-1855 [000] d..1. 7030.530293: cgroup_attach_task: dst_root=3 dst_id=22 dst_level=1 dst_path=/foreground pid=1900 comm=surfaceflinger
TimerDispatch-2768 [002] d..5. 7030.537542: sched_migrate_task: comm=surfaceflinger pid=1900 prio=98 orig_cpu=0 dest_cpu=4
<snip>
"Boosting a task" depends on synchronize_rcu() latency:
- first trace shows a completion of synchronize_rcu();
- second shows attaching a task to a new group;
- last shows a final step when migration occurs.
3. To address this drawback, maintain a separate track that consists
of synchronize_rcu() callers only. After completion of a grace period
users are deferred to a dedicated worker to process requests.
4. This patch reduces the latency of synchronize_rcu() approximately
by ~30-40% on synthetic tests. The real test case, camera launch time,
shows(time is in milliseconds):
1-run 542 vs 489 improvement 9%
2-run 540 vs 466 improvement 13%
3-run 518 vs 468 improvement 9%
4-run 531 vs 457 improvement 13%
5-run 548 vs 475 improvement 13%
6-run 509 vs 484 improvement 4%
Synthetic test(no "noise" from other callbacks):
Hardware: x86_64 64 CPUs, 64GB of memory
Linux-6.6
- 10K tasks(simultaneous);
- each task does(1000 loops)
synchronize_rcu();
kfree(p);
default: CONFIG_RCU_NOCB_CPU: takes 54 seconds to complete all users;
patch: CONFIG_RCU_NOCB_CPU: takes 35 seconds to complete all users.
Running 60K gives approximately same results on my setup. Please note
it is without any interaction with another type of callbacks, otherwise
it will impact a lot a default case.
5. By default it is disabled. To enable this perform one of the
below sequence:
echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp
or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1"
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Co-developed-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Rearrange the instructions so that readers facing a regression within a
stable or longterm series first test its latest release before testing
mainline. This is less scary for some people. It also reduces the chance
that something goes sideways for readers that compile their first
kernel, as mainline can cause slightly more trouble.
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/efd3cb9c68db450091021326bf9c334553df0ec2.1712647788.git.linux@leemhuis.info
Add and fetch all required stable branches ahead of time. This fixes a
bug, as readers that wanted to bisect a regression within a stable or
longterm series otherwise did not have them available at the right time.
This way also matches the flow somewhat better and avoids some "if you
haven't already added it" phrases that otherwise become necessary in
future changes.
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/57dcf312959476abe6151bf3d35eb79e3e9a83d1.1712647788.git.linux@leemhuis.info
Various small improvements and fixes:
* Use the more modern 'git switch' instead of 'git checkout', which
makes it more obvious what's happening (among others due to the
--discard-changes parameter that is more clear than --force).
* Provide a hint how a mainline version number and one from a stable
series look like.
* When trying to validate the bisection result with a revert, add a
special tag to facilitate the identification.
* Sync version numbers used in various examples for consistency: stick
to 6.0.13, 6.0.15, and 6.1.5.
* Fix a few typos and oddities.
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/85029aa004447b0eeb5043fb014630f2acafacec.1712647788.git.linux@leemhuis.info
In order to be able to limit the amount of memory that is allocated
by IOMMU subsystem, the memory must be accounted.
Account IOMMU as part of the secondary pagetables as it was discussed
at LPC.
The value of SecPageTables now contains mmeory allocation by IOMMU
and KVM.
There is a difference between GFP_ACCOUNT and what NR_IOMMU_PAGES shows.
GFP_ACCOUNT is set only where it makes sense to charge to user
processes, i.e. IOMMU Page Tables, but there more IOMMU shared data
that should not really be charged to a specific process.
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Acked-by: David Rientjes <rientjes@google.com>
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20240413002522.1101315-12-pasha.tatashin@soleen.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
When terminal is unresponsive, one cannot use dmesg to view
the printk ring buffer messages. Also, syslog services may be
disabled, especially on embedded systems, to check the messages
after a reboot. In this scenario, replay the messages in printk
ring buffer on consoles via sysrq by pressing sysrq+R.
The console loglevel will determine which all kernel log messages
are displayed. The messages will be displayed only when
console_trylock() succeeds. Users could repeat the sysrq key when
it fails. If the owner of console subsystem lock is stuck,
repeating the key won't work.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Shimoyashiki Taichi <taichi.shimoyashiki@sony.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sreenath Vijayan <sreenath.vijayan@sony.com>
Link: https://lore.kernel.org/r/cc3b9b1aae60a236c6aed1dc7b0ffa2c7cd1f183.1710220326.git.sreenath.vijayan@sony.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Quoting of the '"no regressions" rule' expression differs between
occurrences, sometimes being presented as '"no regressions rule"'. Unify
the quoting using the first form which seems semantically correct or is
at least used dominantly, albeit marginally.
One of the occurrences is obviously missing the 'rule' part -- add it.
Signed-off-by: Karel Balej <balejk@matfyz.cz>
Reviewed-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240328194342.11760-2-balejk@matfyz.cz
Pull x86 mitigations from Thomas Gleixner:
"Mitigations for the native BHI hardware vulnerabilty:
Branch History Injection (BHI) attacks may allow a malicious
application to influence indirect branch prediction in kernel by
poisoning the branch history. eIBRS isolates indirect branch targets
in ring0. The BHB can still influence the choice of indirect branch
predictor entry, and although branch predictor entries are isolated
between modes when eIBRS is enabled, the BHB itself is not isolated
between modes.
Add mitigations against it either with the help of microcode or with
software sequences for the affected CPUs"
[ This also ends up enabling the full mitigation by default despite the
system call hardening, because apparently there are other indirect
calls that are still sufficiently reachable, and the 'auto' case just
isn't hardened enough.
We'll have some more inevitable tweaking in the future - Linus ]
* tag 'nativebhi' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
KVM: x86: Add BHI_NO
x86/bhi: Mitigate KVM by default
x86/bhi: Add BHI mitigation knob
x86/bhi: Enumerate Branch History Injection (BHI) bug
x86/bhi: Define SPEC_CTRL_BHI_DIS_S
x86/bhi: Add support for clearing branch history at syscall entry
x86/syscall: Don't force use of indirect calls for system calls
x86/bugs: Change commas to semicolons in 'spectre_v2' sysfs file
The original description refers to the comment on
cgroup_for_each_descendant_pre() for more details. However, the macro
cgroup_for_each_descendant_pre() no longer exist, we replace it with the
corresponding macro cgroup_for_each_live_descendant_pre().
Signed-off-by: I Hsin Cheng <richard120310@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
BHI mitigation mode spectre_bhi=auto does not deploy the software
mitigation by default. In a cloud environment, it is a likely scenario
where userspace is trusted but the guests are not trusted. Deploying
system wide mitigation in such cases is not desirable.
Update the auto mode to unconditionally mitigate against malicious
guests. Deploy the software sequence at VMexit in auto mode also, when
hardware mitigation is not available. Unlike the force =on mode,
software sequence is not deployed at syscalls in auto mode.
Suggested-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Branch history clearing software sequences and hardware control
BHI_DIS_S were defined to mitigate Branch History Injection (BHI).
Add cmdline spectre_bhi={on|off|auto} to control BHI mitigation:
auto - Deploy the hardware mitigation BHI_DIS_S, if available.
on - Deploy the hardware mitigation BHI_DIS_S, if available,
otherwise deploy the software sequence at syscall entry and
VMexit.
off - Turn off BHI mitigation.
The default is auto mode which does not deploy the software sequence
mitigation. This is because of the hardening done in the syscall
dispatch path, which is the likely target of BHI.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Fix the mgb4 driver documentation structure that breaks the
"Video4Linux (V4L) driver-specific documentation" outline.
Signed-off-by: Martin Tůma <martin.tuma@digiteqautomotive.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
