linux-kernel - [PATCHv5 29/30] ACPICA: Avoid cache flush inside virtual machines

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Message-Id: <20220302142806.51844-30-kirill.shutemov@linux.intel.com>
Date:   Wed,  2 Mar 2022 17:28:05 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...el.com, luto@...nel.org, peterz@...radead.org
Cc:     sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv5 29/30] ACPICA: Avoid cache flush inside virtual machines

WBINVD is not supported in TDX guest and triggers #VE. There's no robust
way to emulate it. The kernel has to avoid it.

ACPI_FLUSH_CPU_CACHE() flushes caches usign WBINVD on entering sleep
states. It is required to prevent data loss.

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.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/include/asm/acenv.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/acenv.h b/arch/x86/include/asm/acenv.h
index 9aff97f0de7f..d937c55e717e 100644
--- a/arch/x86/include/asm/acenv.h
+++ b/arch/x86/include/asm/acenv.h
@@ -13,7 +13,19 @@
 
 /* Asm macros */
 
-#define ACPI_FLUSH_CPU_CACHE()	wbinvd()
+/*
+ * ACPI_FLUSH_CPU_CACHE() flushes caches on entering sleep states.
+ * It is required to prevent data loss.
+ *
+ * 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.
+ */
+#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);
-- 
2.34.1