linux-kernel - [PATCHv4 29/30] ACPICA: Avoid cache flush on TDX guest

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Message-Id: <20220224155630.52734-30-kirill.shutemov@linux.intel.com>
Date:   Thu, 24 Feb 2022 18:56:29 +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: [PATCHv4 29/30] ACPICA: Avoid cache flush on TDX guest

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

While running inside TDX guest, 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.

The approach can be generalized to all guest kernels, but, to be
cautious, let's limit it to TDX for now.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/include/asm/acenv.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/acenv.h b/arch/x86/include/asm/acenv.h
index 9aff97f0de7f..d19deca6dd27 100644
--- a/arch/x86/include/asm/acenv.h
+++ b/arch/x86/include/asm/acenv.h
@@ -13,7 +13,21 @@
 
 /* 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 TDX guest, 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.
+ *
+ * TODO: Is it safe to generalize this from TDX guests to all guest kernels?
+ */
+#define ACPI_FLUSH_CPU_CACHE()					\
+do {								\
+	if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))	\
+		wbinvd();					\
+} while (0)
 
 int __acpi_acquire_global_lock(unsigned int *lock);
 int __acpi_release_global_lock(unsigned int *lock);
-- 
2.34.1