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Marc Zyngier 5fc0933641 arm64: Force the use of CNTVCT_EL0 in __delay() 
[ Upstream commit 29cc0f3aa7 ]

Quentin forwards a report from Hyesoo Yu, describing an interesting
problem with the use of WFxT in __delay() when a vcpu is loaded and
that KVM is *not* in VHE mode (either nVHE or hVHE).

In this case, CNTVOFF_EL2 is set to a non-zero value to reflect the
state of the guest virtual counter. At the same time, __delay() is
using get_cycles() to read the counter value, which is indirected to
reading CNTPCT_EL0.

The core of the issue is that WFxT is using the *virtual* counter,
while the kernel is using the physical counter, and that the offset
introduces a really bad discrepancy between the two.

Fix this by forcing the use of CNTVCT_EL0, making __delay() consistent
irrespective of the value of CNTVOFF_EL2.

Reported-by: Hyesoo Yu <hyesoo.yu@samsung.com>
Reported-by: Quentin Perret <qperret@google.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Fixes: 7d26b0516a ("arm64: Use WFxT for __delay() when possible")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/ktosachvft2cgqd5qkukn275ugmhy6xrhxur4zqpdxlfr3qh5h@o3zrfnsq63od
Cc: stable@vger.kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-03-04 07:21:58 -05:00
arch arm64: Force the use of CNTVCT_EL0 in __delay() 2026-03-04 07:21:58 -05:00
block block: decouple secure erase size limit from discard size limit 2026-03-04 07:20:56 -05:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:28:39 +01:00
Documentation ASoC: dt-bindings: asahi-kasei,ak5558: Fix the supply names 2026-03-04 07:20:48 -05:00
drivers net: ethernet: ec_bhf: Fix dma_free_coherent() dma handle 2026-03-04 07:21:58 -05:00
fs cifs: some missing initializations on replay 2026-03-04 07:21:58 -05:00
include ipv6: ioam: fix heap buffer overflow in __ioam6_fill_trace_data() 2026-03-04 07:21:57 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/filetable: clamp alloc_hint to the configured alloc range 2026-03-04 07:21:56 -05:00
ipc ipc: don't audit capability check in ipc_permissions() 2026-03-04 07:20:07 -05:00
kernel function_graph: Restore direct mode when callbacks drop to one 2026-03-04 07:21:57 -05:00
lib Remove WARN_ALL_UNSEEDED_RANDOM kernel config option 2026-03-04 07:21:32 -05:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: numa_memblks: Identify the accurate NUMA ID of CFMW 2026-03-04 07:21:57 -05:00
net net/sched: act_skbedit: fix divide-by-zero in tcf_skbedit_hash() 2026-03-04 07:21:58 -05:00
rust rust: kbuild: pass -Zunstable-options for Rust 1.95.0 2026-03-04 07:21:54 -05:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:14:50 +01:00
scripts modpost: Amend ppc64 save/restfpr symnames for -Os build 2026-03-04 07:21:09 -05:00
security apparmor: fix aa_label to return state from compount and component match 2026-03-04 07:20:41 -05:00
sound ASoC: amd: yc: Add DMI quirk for ASUS Vivobook Pro 15X M6501RR 2026-03-04 07:21:58 -05:00
tools tools: Fix bitfield dependency failure 2026-03-04 07:21:50 -05:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:40:17 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS gpiolib-acpi: Update file references in the Documentation and MAINTAINERS 2026-02-11 13:40:29 +01:00
Makefile kbuild: Add objtool to top-level clean target 2026-03-04 07:20:35 -05:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.