linux-kernel - [PATCH v6 2/8] x86/sev: Add support for the RMPREAD instruction

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Message-ID: <72c734ac8b324bbc0c839b2c093a11af4a8881fa.1733172653.git.thomas.lendacky@amd.com>
Date: Mon, 2 Dec 2024 14:50:47 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: <linux-kernel@...r.kernel.org>, <x86@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>,
	Nikunj A Dadhania <nikunj@....com>, Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Subject: [PATCH v6 2/8] x86/sev: Add support for the RMPREAD instruction

The RMPREAD instruction returns an architecture defined format of an
RMP table entry. This is the preferred method for examining RMP entries.

The instruction is advertised in CPUID 0x8000001f_EAX[21]. Use this
instruction when available.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
Reviewed-by: Nikunj A Dadhania <nikunj@....com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Reviewed-by: Ashish Kalra <ashish.kalra@....com>
---
 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/virt/svm/sev.c            | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 17b6590748c0..5535edc6e8d7 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -451,6 +451,7 @@
 #define X86_FEATURE_V_TSC_AUX		(19*32+ 9) /* Virtual TSC_AUX */
 #define X86_FEATURE_SME_COHERENT	(19*32+10) /* AMD hardware-enforced cache coherency */
 #define X86_FEATURE_DEBUG_SWAP		(19*32+14) /* "debug_swap" AMD SEV-ES full debug state swap support */
+#define X86_FEATURE_RMPREAD		(19*32+21) /* RMPREAD instruction */
 #define X86_FEATURE_SVSM		(19*32+28) /* "svsm" SVSM present */
 
 /* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word 20 */
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index cf64e9384ea0..18191cbd78c5 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -306,6 +306,18 @@ static int get_rmpentry(u64 pfn, struct rmpentry *e)
 {
 	struct rmpentry_raw *e_raw;
 
+	if (cpu_feature_enabled(X86_FEATURE_RMPREAD)) {
+		int ret;
+
+		/* Binutils version 2.44 supports the RMPREAD mnemonic. */
+		asm volatile(".byte 0xf2, 0x0f, 0x01, 0xfd"
+			     : "=a" (ret)
+			     : "a" (pfn << PAGE_SHIFT), "c" (e)
+			     : "memory", "cc");
+
+		return ret;
+	}
+
 	e_raw = get_raw_rmpentry(pfn);
 	if (IS_ERR(e_raw))
 		return PTR_ERR(e_raw);
-- 
2.46.2