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Mark Rutland bfcaffd4cc arm64: smccc: Remove broken support for SMCCCv1.3 SVE discard hint 
commit 8c462d5648 upstream.

SMCCCv1.3 added a hint bit which callers can set in an SMCCC function ID
(AKA "FID") to indicate that it is acceptable for the SMCCC
implementation to discard SVE and/or SME state over a specific SMCCC
call. The kernel support for using this hint is broken and SMCCC calls
may clobber the SVE and/or SME state of arbitrary tasks, though FPSIMD
state is unaffected.

The kernel support is intended to use the hint when there is no SVE or
SME state to save, and to do this it checks whether TIF_FOREIGN_FPSTATE
is set or TIF_SVE is clear in assembly code:

|        ldr     <flags>, [<current_task>, #TSK_TI_FLAGS]
|        tbnz    <flags>, #TIF_FOREIGN_FPSTATE, 1f   // Any live FP state?
|        tbnz    <flags>, #TIF_SVE, 2f               // Does that state include SVE?
|
| 1:     orr     <fid>, <fid>, ARM_SMCCC_1_3_SVE_HINT
| 2:
|        << SMCCC call using FID >>

This is not safe as-is:

(1) SMCCC calls can be made in a preemptible context and preemption can
    result in TIF_FOREIGN_FPSTATE being set or cleared at arbitrary
    points in time. Thus checking for TIF_FOREIGN_FPSTATE provides no
    guarantee.

(2) TIF_FOREIGN_FPSTATE only indicates that the live FP/SVE/SME state in
    the CPU does not belong to the current task, and does not indicate
    that clobbering this state is acceptable.

    When the live CPU state is clobbered it is necessary to update
    fpsimd_last_state.st to ensure that a subsequent context switch will
    reload FP/SVE/SME state from memory rather than consuming the
    clobbered state. This and the SMCCC call itself must happen in a
    critical section with preemption disabled to avoid races.

(3) Live SVE/SME state can exist with TIF_SVE clear (e.g. with only
    TIF_SME set), and checking TIF_SVE alone is insufficient.

Remove the broken support for the SMCCCv1.3 SVE saving hint. This is
effectively a revert of commits:

* cfa7ff959a ("arm64: smccc: Support SMCCC v1.3 SVE register saving hint")
* a7c3acca53 ("arm64: smccc: Save lr before calling __arm_smccc_sve_check()")

... leaving behind the ARM_SMCCC_VERSION_1_3 and ARM_SMCCC_1_3_SVE_HINT
definitions, since these are simply definitions from the SMCCC
specification, and the latter is used in KVM via ARM_SMCCC_CALL_HINTS.

If we want to bring this back in future, we'll probably want to handle
this logic in C where we can use all the usual FPSIMD/SVE/SME helper
functions, and that'll likely require some rework of the SMCCC code
and/or its callers.

Fixes: cfa7ff959a ("arm64: smccc: Support SMCCC v1.3 SVE register saving hint")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241106160448.2712997-1-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
[ Mark: fix conflicts in <linux/arm-smccc.h> ]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2024-12-14 19:54:53 +01:00
arch arm64: smccc: Remove broken support for SMCCCv1.3 SVE discard hint 2024-12-14 19:54:53 +01:00
block block: fix ordering between checking BLK_MQ_S_STOPPED request adding 2024-12-14 19:54:04 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: api - Add crypto_clone_tfm 2024-12-14 19:53:51 +01:00
Documentation PCI: Add 'reset_subordinate' to reset hierarchy below bridge 2024-12-14 19:54:48 +01:00
drivers arm64: smccc: Remove broken support for SMCCCv1.3 SVE discard hint 2024-12-14 19:54:53 +01:00
fs ocfs2: Revert "ocfs2: fix the la space leak when unmounting an ocfs2 volume" 2024-12-14 19:54:52 +01:00
include arm64: smccc: Remove broken support for SMCCCv1.3 SVE discard hint 2024-12-14 19:54:53 +01:00
init initramfs: avoid filename buffer overrun 2024-12-14 19:53:14 +01:00
io_uring io_uring: wake up optimisations 2024-12-14 19:54:52 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-14 19:54:06 +01:00
kernel tracing/eprobe: Fix to release eprobe when failed to add dyn_event 2024-12-14 19:54:50 +01:00
lib lib: stackinit: hide never-taken branch from compiler 2024-12-14 19:54:37 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/damon/vaddr: fix issue in damon_va_evenly_split_region() 2024-12-14 19:54:52 +01:00
net netpoll: Use rcu_access_pointer() in __netpoll_setup 2024-12-14 19:54:45 +01:00
rust rust: macros: provide correct provenance when constructing THIS_MODULE 2024-10-17 15:22:24 +02:00
samples samples/bpf: Fix a resource leak 2024-12-14 19:54:40 +01:00
scripts modpost: Add .irqentry.text to OTHER_SECTIONS 2024-12-14 19:54:35 +01:00
security apparmor: test: Fix memory leak for aa_unpack_strdup() 2024-12-14 19:53:59 +01:00
sound ASoC: amd: yc: Add quirk for microphone on Lenovo Thinkpad T14s Gen 6 21M1CTO1WW 2024-12-14 19:54:49 +01:00
tools verification/dot2: Improve dot parser robustness 2024-12-14 19:54:47 +01:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin() 2024-06-27 13:46:21 +02:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:21:15 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -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 Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
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 MAINTAINERS: add leah to 6.1 MAINTAINERS file 2024-05-17 11:56:16 +02:00
Makefile Linux 6.1.119 2024-11-22 15:37:35 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.