Re: [PATCH v4 1/2] x86/sev: Clear RMPOPT when segmented RMP is disabled by firmware

[Borislav Petkov]

Ok,

pls check if this works too:

From: Ashish Kalra <ashish.kalra@xxxxxxx>
Date: Wed, 28 Oct 2026 19:49:22 +0000
Subject: [PATCH] x86/sev: Clear RMPOPT when segmented RMP is disabled by firmware

Segmented RMP support is advertised via X86_FEATURE_SEGMENTED_RMP, and the
firmware enables it via MSR_AMD64_RMP_CFG[SEG_RMP_ENABLED]. The latter can be
cleared in platform BIOS by the user, in which case the system runs in
contiguous RMP setting.

snp_probe_rmptable_info() does not clear X86_FEATURE_RMPOPT in the
advertised-but-firmware-disabled case.

As a result, this does not prevent snp_enable_rmpopt() from trying to program
MSR_AMD64_RMPOPT_BASE, which raises a #GP on the MSR access.

Make sure X86_FEATURE_RMPOPT is cleared in all cases where segmented RMP is
not enabled.

  [ bp:
   - Put the commit message on Ozempic
   - Flip the logic in the function so that the segmented RMP disabled
     case goes first and the flow gets simpler this way. ]

Fixes: 15d974be0a3b ("x86/sev: Initialize RMPOPT configuration MSRs")
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://patch.msgid.link/56da047d63b22f03a7e709fc172a5543da894d67.1793216372.git.ashish.kalra@xxxxxxx
---
 arch/x86/virt/svm/sev.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index bd70c4d0b774..ff6d17795054 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -817,21 +817,20 @@ static bool probe_segmented_rmptable_info(void)
 
 bool snp_probe_rmptable_info(void)
 {
-	if (cpu_feature_enabled(X86_FEATURE_SEGMENTED_RMP)) {
-		rdmsrq(MSR_AMD64_RMP_CFG, rmp_cfg);
+	if (!cpu_feature_enabled(X86_FEATURE_SEGMENTED_RMP)) {
+		setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
 
-		if (rmp_cfg & MSR_AMD64_SEG_RMP_ENABLED) {
-			if (probe_segmented_rmptable_info())
-				return true;
+		return probe_contiguous_rmptable_info();
+	}
 
-			setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
-			return false;
-		}
-	} else {
-		setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
+	rdmsrq(MSR_AMD64_RMP_CFG, rmp_cfg);
+	if (rmp_cfg & MSR_AMD64_SEG_RMP_ENABLED) {
+		if (probe_segmented_rmptable_info())
+			return true;
 	}
 
-	return probe_contiguous_rmptable_info();
+	setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
+	return false;
 }
 
 /*
-- 
2.53.0

-- 
Regards/Gruss,
    Boris.

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