[PATCH 0/2] x86/sev: Fix RMPOPT enablement on non-RMPOPT configs

[PATCH 0/2] x86/sev: Fix RMPOPT enablement on non-RMPOPT configs

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

Two fixes for the RMPOPT series, both for configurations where the
RMPOPT CPUID bit is advertised but RMPOPT is not actually usable:

Patch 1 clears X86_FEATURE_RMPOPT when the platform advertises segmented
RMP but the firmware has it disabled (contiguous RMP) - otherwise the
RMPOPT initcall programs RMPOPT_BASE and issues RMPOPT, which #GP.

Patch 2 moves the "RMPOPT optimizations enabled" message out of the
feature-only-gated initcall and into the SNP-gated enable path, so it is
not printed when SNP is disabled in the BIOS.

Both restore the behaviour of the posted series; the issues were
introduced when the series was applied (see the per-patch notes). Each
carries a Fixes: tag.

Ashish Kalra (2):
  x86/sev: Clear RMPOPT when segmented RMP is disabled by firmware
  x86/sev: Only announce RMPOPT optimizations when SNP is enabled

 arch/x86/virt/svm/sev.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)


base-commit: 250ee734115bca1c1f7a38d838909aa83cce87ae
-- 
2.43.0

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

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

snp_probe_rmptable_info() only clears X86_FEATURE_RMPOPT when the platform
does not advertise X86_FEATURE_SEGMENTED_RMP, or when the segmented RMP
table probe fails.  It misses the case where the platform advertises
segmented RMP but the firmware has it disabled (MSR_AMD64_RMP_CFG's
SEG_RMP_ENABLED bit is clear), so the system runs with a contiguous RMP:
that path falls through to the contiguous probe with X86_FEATURE_RMPOPT
still set.

X86_FEATURE_RMPOPT is a CPUID bit advertised independently of whether
segmented RMP is enabled, but RMPOPT requires an enabled segmented RMP.
With the capability left set, the RMPOPT initcall programs RMPOPT_BASE and
issues the RMPOPT instruction, both of which #GP on a contiguous RMP:

  unchecked MSR access error: WRMSR to 0xc0010139 ...
  general protection fault ... snp_enable_rmpopt

Clear X86_FEATURE_RMPOPT on the common contiguous fall-through so it covers
both "segmented RMP not supported" and "segmented RMP supported but
disabled by firmware".  The clear runs at BSP init before alternatives, so
the subsequent cpu_feature_enabled(X86_FEATURE_RMPOPT) checks observe it.

Fixes: 15d974be0a3b ("x86/sev: Initialize RMPOPT configuration MSRs")
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---

Note: this restores the snp_probe_rmptable_info() structure from the
posted series (v16 3/5), where a single setup_clear_cpu_cap() on the
common contiguous fall-through covered the "SEGMENTED_RMP advertised but
disabled by firmware" case (called out in the v16 cover letter).  When
applied, 15d974be0a3b narrowed that clear into an else branch and dropped
that case.
 arch/x86/virt/svm/sev.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index bd70c4d0b774..43e4945e6cdf 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -827,10 +827,16 @@ bool snp_probe_rmptable_info(void)
 			setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
 			return false;
 		}
-	} else {
-		setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
 	}
 
+	/*
+	 * Segmented RMP is either not supported on the platform or is
+	 * disabled by the firmware.  RMPOPT is not supported without
+	 * segmented RMP, so drop the capability before it reaches the
+	 * initcall and faults programming RMPOPT_BASE / issuing RMPOPT.
+	 */
+	setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
+
 	return probe_contiguous_rmptable_info();
 }
 
-- 
2.43.0

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

[Borislav Petkov]

On Tue, Oct 13, 2026 at 03:44:18PM +0000, Ashish Kalra wrote:
> snp_probe_rmptable_info() only clears X86_FEATURE_RMPOPT when the platform
> does not advertise X86_FEATURE_SEGMENTED_RMP, or when the segmented RMP
> table probe fails.  It misses the case where the platform advertises
> segmented RMP but the firmware has it disabled (MSR_AMD64_RMP_CFG's
> SEG_RMP_ENABLED bit is clear)

What does that mean: "the platform advertises segmented RMP"?

The CPUID bit is still set?

Or anything else?

How do you create this configuration?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

[PATCH 2/2] x86/sev: Only announce RMPOPT optimizations when SNP is enabled

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

rmpopt_init() prints "RMPOPT optimizations enabled" gated only on
X86_FEATURE_RMPOPT, which is a CPUID bit advertised independently of
whether SNP is active.  On a system where SNP is disabled in the BIOS the
message is still printed at boot even though RMPOPT is never actually used
(snp_enable_rmpopt() bails out on !CC_ATTR_HOST_SEV_SNP), which is
misleading.

rmpopt_init() is only the software setup (workqueue and the delayed work);
the capability that matters for the message - an active SNP host - is
checked in snp_enable_rmpopt().  Move the announcement there, as a
pr_info_once(), so it is emitted only when RMPOPT is actually enabled on an
SNP host.

Fixes: c6c6f156d192 ("x86/sev: Perform RMP optimizations asynchronously")
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---

Note: in the posted series the pr_info_once() lived in
snp_enable_rmpopt() (SNP-gated); when applied, c6c6f156d192 moved it to
rmpopt_init() (feature-only-gated) as a plain pr_info().  This restores the
original placement.
 arch/x86/virt/svm/sev.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 43e4945e6cdf..6f5f4ee821d0 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -656,8 +656,6 @@ static int __init rmpopt_init(void)
 	if ((rmpopt_pa_end - rmpopt_pa_start) > SZ_2T)
 		rmpopt_pa_end = rmpopt_pa_start + SZ_2T;
 
-	pr_info("RMPOPT optimizations enabled\n");
-
 	rmpopt_soft_init = true;
 
 	return 0;
@@ -690,6 +688,8 @@ void snp_enable_rmpopt(void)
 
 	mod_delayed_work(rmpopt_wq, &rmpopt_delayed_work,
 			 msecs_to_jiffies(RMPOPT_WORK_TIMEOUT));
+
+	pr_info_once("RMPOPT optimizations enabled\n");
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_enable_rmpopt, "ccp,kvm-amd");
 
-- 
2.43.0