Re: [PATCH v1 2/2] x86/sev: Add SNP-specific unaccepted memory support

[Dionna Amalie Glaze]

>
> +void snp_accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +       unsigned long vaddr;
> +       unsigned int npages;
> +
> +       if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> +               return;
> +
> +       vaddr = (unsigned long)__va(start);
> +       npages = (end - start) >> PAGE_SHIFT;
> +
> +       set_pages_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE);
> +
> +       pvalidate_pages(vaddr, npages, true);
> +}

My testing of this patch shows that a significant amount of time is
spent using the MSR protocol to change page state, in such a
significant fashion that it's slower than eagerly accepting all
memory. The difference gets worse as the RAM size goes up, so I think
there's some phase problem with the GHCB protocol not getting used
early enough?

-- 
-Dionna Glaze, PhD (she/her)