From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "Rafael J . Wysocki" <rjw@rjwysocki.net>
Cc: "H . Peter Anvin" <hpa@zytor.com>,
Tony Luck <tony.luck@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Andi Kleen <ak@linux.intel.com>,
Kirill Shutemov <kirill.shutemov@linux.intel.com>,
Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: [PATCH v2] x86: Skip WBINVD instruction for VM guest
Date: Thu, 18 Nov 2021 20:03:30 -0800 [thread overview]
Message-ID: <20211119040330.4013045-1-sathyanarayanan.kuppuswamy@linux.intel.com> (raw)
In-Reply-To: <YZPbQVwWOJCrAH78@zn.tnic>
ACPI mandates that CPU caches be flushed before entering any sleep
state. This ensures that the CPU and its caches can be powered down
without losing data.
ACPI-based VMs have maintained this sleep-state-entry behavior.
However, cache flushing for VM sleep state entry is useless. Unlike on
bare metal, guest sleep states are not correlated with potential data
loss of any kind; the host is responsible for data preservation. In
fact, some KVM configurations simply skip the cache flushing
instruction (see need_emulate_wbinvd()).
Further, on TDX systems, the WBINVD instruction causes an
unconditional #VE exception. If this cache flushing remained, it would
need extra code in the form of a #VE handler.
All use of ACPI_FLUSH_CPU_CACHE() appears to be in sleep-state-related
code.
This means that the ACPI use of WBINVD is at *best* superfluous.
Disable ACPI CPU cache flushing on all X86_FEATURE_HYPERVISOR systems,
which includes TDX.
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-acpi@vger.kernel.org
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
Changes since v1:
* Used cpu_feature_enabled() instead of boot_cpu_has().
arch/x86/include/asm/acenv.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/acenv.h b/arch/x86/include/asm/acenv.h
index 9aff97f0de7f..dba05c74bd7e 100644
--- a/arch/x86/include/asm/acenv.h
+++ b/arch/x86/include/asm/acenv.h
@@ -10,10 +10,15 @@
#define _ASM_X86_ACENV_H
#include <asm/special_insns.h>
+#include <asm/cpu.h>
/* Asm macros */
-#define ACPI_FLUSH_CPU_CACHE() wbinvd()
+#define ACPI_FLUSH_CPU_CACHE() \
+do { \
+ if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) \
+ wbinvd(); \
+} while (0)
int __acpi_acquire_global_lock(unsigned int *lock);
int __acpi_release_global_lock(unsigned int *lock);
--
2.25.1
next prev parent reply other threads:[~2021-11-19 4:03 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-16 0:50 [PATCH v1 1/1] x86: Skip WBINVD instruction for VM guest Kuppuswamy Sathyanarayanan
2021-11-16 16:24 ` Borislav Petkov
2021-11-16 16:36 ` Sathyanarayanan Kuppuswamy
2021-11-19 4:03 ` Kuppuswamy Sathyanarayanan [this message]
2021-11-25 0:40 ` [PATCH v2] " Thomas Gleixner
2021-12-02 22:21 ` Kirill A. Shutemov
2021-12-02 22:38 ` Dave Hansen
2021-12-02 23:48 ` Thomas Gleixner
2021-12-03 23:49 ` Kirill A. Shutemov
2021-12-04 0:20 ` Dave Hansen
2021-12-04 0:54 ` Kirill A. Shutemov
2021-12-06 15:35 ` Dave Hansen
2021-12-06 16:39 ` Dan Williams
2021-12-06 16:53 ` Dave Hansen
2021-12-06 17:51 ` Dan Williams
2021-12-04 20:27 ` Rafael J. Wysocki
2021-12-06 12:29 ` [PATCH 0/4] ACPI/ACPICA: Only flush caches on S1/S2/S3 and C3 Kirill A. Shutemov
2021-12-06 12:29 ` [PATCH 1/4] ACPICA: Do not flush cache for on entering S4 and S5 Kirill A. Shutemov
2021-12-08 14:58 ` Rafael J. Wysocki
2021-12-06 12:29 ` [PATCH 2/4] ACPI: PM: Remove redundant cache flushing Kirill A. Shutemov
2021-12-07 16:35 ` Rafael J. Wysocki
2021-12-09 13:32 ` Kirill A. Shutemov
2021-12-17 18:04 ` Rafael J. Wysocki
2021-12-06 12:29 ` [PATCH 3/4] ACPI: processor idle: Only flush cache on entering C3 Kirill A. Shutemov
2021-12-06 15:03 ` Peter Zijlstra
2021-12-08 16:26 ` Rafael J. Wysocki
2021-12-09 13:33 ` Kirill A. Shutemov
2021-12-17 17:58 ` Rafael J. Wysocki
2021-12-06 12:29 ` [PATCH 4/4] ACPI: PM: Avoid cache flush on entering S4 Kirill A. Shutemov
2021-12-08 15:10 ` Rafael J. Wysocki
2021-12-08 16:04 ` Kirill A. Shutemov
2021-12-08 16:16 ` Rafael J. Wysocki
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