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Kirill A. Shutemov 8ded0af90e ACPICA: Avoid cache flush inside virtual machines
[ Upstream commit e2efb6359e620521d1e13f69b2257de8ceaa9475 ]

While running inside virtual machine, the kernel can bypass cache
flushing. Changing sleep state in a virtual machine doesn't affect the
host system sleep state and cannot lead to data loss.

Before entering sleep states, the ACPI code flushes caches to prevent
data loss using the WBINVD instruction.  This mechanism is required on
bare metal.

But, any use WBINVD inside of a guest is worthless.  Changing sleep
state in a virtual machine doesn't affect the host system sleep state
and cannot lead to data loss, so most hypervisors simply ignore it.
Despite this, the ACPI code calls WBINVD unconditionally anyway.
It's useless, but also normally harmless.

In TDX guests, though, WBINVD stops being harmless; it triggers a
virtualization exception (#VE).  If the ACPI cache-flushing WBINVD
were left in place, TDX guests would need handling to recover from
the exception.

Avoid using WBINVD whenever running under a hypervisor.  This both
removes the useless WBINVDs and saves TDX from implementing WBINVD
handling.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20220405232939.73860-30-kirill.shutemov@linux.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-06-14 18:11:25 +02:00
arch ACPICA: Avoid cache flush inside virtual machines 2022-06-14 18:11:25 +02:00
block block: return ELEVATOR_DISCARD_MERGE if possible 2022-05-25 09:14:38 +02:00
certs certs: Trigger creation of RSA module signing key if it's not an RSA key 2021-09-15 09:47:29 +02:00
crypto crypto: ecrdsa - Fix incorrect use of vli_cmp 2022-06-06 08:33:50 +02:00
Documentation docs: submitting-patches: Fix crossref to 'The canonical patch format' 2022-06-06 08:33:51 +02:00
drivers fbcon: Consistently protect deferred_takeover with console_lock() 2022-06-14 18:11:25 +02:00
fs btrfs: repair super block num_devices automatically 2022-06-14 18:11:24 +02:00
include ipv6: fix locking issues with loops over idev->addr_list 2022-06-14 18:11:25 +02:00
init init/main.c: return 1 from handled __setup() functions 2022-04-15 14:18:35 +02:00
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-12-01 09:23:35 +01:00
kernel ptrace: Reimplement PTRACE_KILL by always sending SIGKILL 2022-06-14 18:11:24 +02:00
lib assoc_array: Fix BUG_ON during garbage collect 2022-06-06 08:33:50 +02:00
LICENSES
mm zsmalloc: fix races between asynchronous zspage free and page migration 2022-06-06 08:33:50 +02:00
net ipv6: fix locking issues with loops over idev->addr_list 2022-06-14 18:11:25 +02:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-17 09:48:39 +01:00
scripts gcc-plugins: latent_entropy: use /dev/urandom 2022-04-20 09:19:38 +02:00
security lockdown: also lock down previous kgdb use 2022-06-06 08:33:48 +02:00
sound ALSA: hda/realtek - Fix microphone noise on ASUS TUF B550M-PLUS 2022-06-14 18:11:23 +02:00
tools x86/xen: Mark cpu_bringup_and_idle() as dead_end_function 2022-05-25 09:14:38 +02:00
usr
virt KVM: Prevent module exit until all VMs are freed 2022-04-15 14:18:27 +02:00
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Makefile Linux 5.4.197 2022-06-06 08:33:51 +02:00
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.