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Mark Rutland 407a99c465 KVM: arm64: Remove VHE host restore of CPACR_EL1.SMEN 
When KVM is in VHE mode, the host kernel tries to save and restore the
configuration of CPACR_EL1.SMEN (i.e. CPTR_EL2.SMEN when HCR_EL2.E2H=1)
across kvm_arch_vcpu_load_fp() and kvm_arch_vcpu_put_fp(), since the
configuration may be clobbered by hyp when running a vCPU. This logic
has historically been broken, and is currently redundant.

This logic was originally introduced in commit:

  861262ab86 ("KVM: arm64: Handle SME host state when running guests")

At the time, the VHE hyp code would reset CPTR_EL2.SMEN to 0b00 when
returning to the host, trapping host access to SME state. Unfortunately,
this was unsafe as the host could take a softirq before calling
kvm_arch_vcpu_put_fp(), and if a softirq handler were to use kernel mode
NEON the resulting attempt to save the live FPSIMD/SVE/SME state would
result in a fatal trap.

That issue was limited to VHE mode. For nVHE/hVHE modes, KVM always
saved/restored the host kernel's CPACR_EL1 value, and configured
CPTR_EL2.TSM to 0b0, ensuring that host usage of SME would not be
trapped.

The issue above was incidentally fixed by commit:

  375110ab51 ("KVM: arm64: Fix resetting SME trap values on reset for (h)VHE")

That commit changed the VHE hyp code to configure CPTR_EL2.SMEN to 0b01
when returning to the host, permitting host kernel usage of SME,
avoiding the issue described above. At the time, this was not identified
as a fix for commit 861262ab86.

Now that the host eagerly saves and unbinds its own FPSIMD/SVE/SME
state, there's no need to save/restore the state of the EL0 SME trap.
The kernel can safely save/restore state without trapping, as described
above, and will restore userspace state (including trap controls) before
returning to userspace.

Remove the redundant logic.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-5-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
2025-02-13 17:54:54 +00:00
arch KVM: arm64: Remove VHE host restore of CPACR_EL1.SMEN 2025-02-13 17:54:54 +00:00
block block: Fix potential deadlock while freezing queue and acquiring sysfs_lock 2024-12-13 10:51:58 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: rsassa-pkcs1 - Copy source data for SG list 2024-12-10 13:34:05 +08:00
Documentation Merge branch kvm-arm64/misc-6.14 into kvmarm-master/next 2025-01-17 11:06:50 +00:00
drivers arm64/sysreg: Get rid of TRFCR_ELx SysregFields 2025-01-17 11:07:55 +00:00
fs First batch of EFI fixes for v6.13 2024-12-15 15:33:41 -08:00
include Merge branch kvm-arm64/pkvm-memshare-declutter into kvmarm-master/next 2025-01-17 11:05:18 +00:00
init - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
io_uring io_uring/rsrc: don't put/free empty buffers 2024-12-12 08:01:52 -07:00
ipc - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
kernel - Prevent incorrect dequeueing of the deadline dlserver helper task and fix 2024-12-15 09:38:03 -08:00
lib - Remove if_not_guard() as it is generating incorrect code 2024-12-09 10:34:41 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm slab fixes for 6.13-rc3 2024-12-13 09:43:50 -08:00
net BPF fixes: 2024-12-14 12:58:14 -08:00
rust rust: kbuild: set bindgen's Rust target version 2024-12-10 01:06:10 +01:00
samples BPF fixes: 2024-12-06 15:07:48 -08:00
scripts A single fix for a docs-build regression caused by the EXPORT_SYMBOL_NS() 2024-12-13 09:46:02 -08:00
security Including fixes from can and netfilter. 2024-12-05 10:25:06 -08:00
sound ASoC: Fixes for v6.13 2024-12-12 14:49:35 +01:00
tools Merge branch kvm-arm64/coresight-6.14 into kvmarm-master/next 2025-01-17 11:05:44 +00:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt VFIO updates for v6.13 2024-11-27 12:57:03 -08:00
.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: enable Clippy's check-private-items 2024-10-07 21:39:57 +02:00
.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 MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.13 2024-11-30 13:41:50 -08:00
.mailmap media updates for v6.13-rc1 2024-11-20 14:01:15 -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 cgroup: Changes for v6.13 2024-11-20 09:54:49 -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 block-6.13-20241213 2024-12-13 15:10:59 -08:00
Makefile Linux 6.13-rc3 2024-12-15 15:58:23 -08:00
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.