Re: [PATCH v10 2/6] x86/sev: Initialize RMPOPT configuration MSRs

[K Prateek Nayak]

Hello Ashish,

On 7/21/2026 7:56 PM, Kalra, Ashish wrote:
> That's why v7 moved to a runtime check. In v11 (as i mentioned) this will be a small local helper,  it will also handles two things
> the cap-clear can't:
>   - a contiguous (non-segmented) RMP, where RMPOPT isn't usable even with X86_FEATURE_RMPOPT set.
>   - SNP being disabled at runtime (CC_ATTR_HOST_SEV_SNP).
> 
>   static bool rmpopt_capable(void)
>   {
>         return cpu_feature_enabled(X86_FEATURE_RMPOPT) &&
>                cc_platform_has(CC_ATTR_HOST_SEV_SNP) &&

CC_ATTR_HOST_SEV_SNP is set from bsp_determine_snp() ...

>                (rmp_cfg & MSR_AMD64_SEG_RMP_ENABLED) &&

... and that already checks snp_probe_rmptable_info() ...

>                rmp_segment_table;

.. and if iommu_snp_enable() fails snp_rmptable_init(), we clear
CC_ATTR_HOST_SEV_SNP.

So, the way I see it, CC_ATTR_HOST_SEV_SNP being set means we have
already tried provisioning RMP table.

I'm assuming all platforms that have  X86_FEATURE_RMPOPT will all have
segmented RMP. If not, you can just clear X86_FEATURE_RMPOPT in
snp_rmptable_init() no?

We can never reach functions that need rmpopt_capable() without
first checking CC_ATTR_HOST_SEV_SNP.

-- 
Thanks and Regards,
Prateek