From: "Kalra, Ashish" <ashish.kalra@amd.com>
To: Borislav Petkov <bp@alien8.de>
Cc: tglx@kernel.org, mingo@redhat.com, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, seanjc@google.com,
peterz@infradead.org, thomas.lendacky@amd.com,
herbert@gondor.apana.org.au, davem@davemloft.net,
ardb@kernel.org, pbonzini@redhat.com, aik@amd.com,
Michael.Roth@amd.com, KPrateek.Nayak@amd.com,
Tycho.Andersen@amd.com, Nathan.Fontenot@amd.com,
ackerleytng@google.com, jackyli@google.com, pgonda@google.com,
rientjes@google.com, jacobhxu@google.com, xin@zytor.com,
pawan.kumar.gupta@linux.intel.com, babu.moger@amd.com,
dyoung@redhat.com, nikunj@amd.com, darwi@linutronix.de,
linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
kvm@vger.kernel.org, linux-coco@lists.linux.dev
Subject: Re: [PATCH 1/2] x86/sev: Clear RMPOPT when segmented RMP is disabled by firmware
Date: Tue, 13 Oct 2026 18:24:19 -0500 [thread overview]
Message-ID: <4d46de3d-6205-4352-9fb4-9cefeb217882@amd.com> (raw)
In-Reply-To: <20261013222653.GAas6wLTEwIw9Te240@fat_crate.local>
On 10/13/2026 5:26 PM, Borislav Petkov wrote:
> 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?
Yes, "Advertises" is the X86_FEATURE_SEGMENTED_RMP CPUID bit set. That's separate from segmented RMP being enabled,
which is MSR_AMD64_RMP_CFG[SEG_RMP_ENABLED] (0xc0010136, bit 0), programmed by firmware
>
> Or anything else?
>
> How do you create this configuration?
There is a BIOS option to enable/disable Segmented RMP. Disabling it on a part that supports/advertises segmented RMP
feature brings the RMP up contiguous (SEG_RMP_ENABLED clear) while the SEGMENTED_RMP CPUID bit stays set.
Thanks,
Ashish
>
> Thx.
>
next prev parent reply other threads:[~2026-10-13 23:24 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-13 15:44 [PATCH 0/2] x86/sev: Fix RMPOPT enablement on non-RMPOPT configs Ashish Kalra
2026-10-13 15:44 ` [PATCH 1/2] x86/sev: Clear RMPOPT when segmented RMP is disabled by firmware Ashish Kalra
2026-10-13 22:26 ` Borislav Petkov
2026-10-13 23:24 ` Kalra, Ashish [this message]
2026-10-14 13:21 ` Tom Lendacky
2026-10-13 15:44 ` [PATCH 2/2] x86/sev: Only announce RMPOPT optimizations when SNP is enabled Ashish Kalra
2026-10-14 13:24 ` Tom Lendacky
2026-10-14 19:33 ` Kalra, Ashish
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