Re: [PATCH v2 2/7] x86/sev: add support for enabling RMPOPT

[Borislav Petkov <bp@alien8.de>]

On Mon, Mar 02, 2026 at 09:35:55PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> The new RMPOPT instruction sets bits in a per-CPU RMPOPT table, which
> indicates whether specific 1GB physical memory regions contain SEV-SNP

"... which indicate... "

> guest memory.
> 
> Per-CPU RMPOPT tables support at most 2 TB of addressable memory for
> RMP optimizations.
> 
> Initialize the per-CPU RMPOPT table base to the starting physical
> address. This enables RMP optimization for up to 2 TB of system RAM on
> all CPUs.

...

> +static void __configure_rmpopt(void *val)
> +{
> +	u64 rmpopt_base = ((u64)val & PUD_MASK) | MSR_AMD64_RMPOPT_ENABLE;
> +
> +	wrmsrq(MSR_AMD64_RMPOPT_BASE, rmpopt_base);
> +}
> +
> +static __init void configure_and_enable_rmpopt(void)

If the sub-helper is called __configure_rmpopt() then this should be called
"configure_rmpopt", without the prepended underscores.

> +	phys_addr_t pa_start = ALIGN_DOWN(PFN_PHYS(min_low_pfn), PUD_SIZE);
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_RMPOPT)) {
> +		pr_debug("RMPOPT not supported on this platform\n");
> +		return;
> +	}
> +
> +	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP)) {
> +		pr_debug("RMPOPT optimizations not enabled as SNP support is not enabled\n");
> +		return;
> +	}

Zap this one - snp_rmptable_init() already checked it.

Also, zap those pr_debugs - you have that information elsewhere already.

> +
> +	if (!(rmp_cfg & MSR_AMD64_SEG_RMP_ENABLED)) {

You can't test this one - you need to test the result of
setup_segmented_rmptable() and whether it did set up the segmented RMP
properly. Only then you can continue here.

> +		pr_info("RMPOPT optimizations not enabled, segmented RMP required\n");

This looks like pr_notice() to me.

> +		return;
> +	}

-- 
Regards/Gruss,
    Boris.

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