Re: [PATCH v8 12/40] x86/sev: Add helper for validating pages in early enc attribute changes

Venu Busireddy
2022-01-03T23:29:45Z

On 2021-12-10 09:43:04 -0600, Brijesh Singh wrote:
> The early_set_memory_{encrypt,decrypt}() are used for changing the

s/encrypt,decrypt/encrypted,decrypted/

> page from decrypted (shared) to encrypted (private) and vice versa.
> When SEV-SNP is active, the page state transition needs to go through
> additional steps.
>
> If the page is transitioned from shared to private, then perform the
> following after the encryption attribute is set in the page table:
>
> 1. Issue the page state change VMGEXIT to add the page as a private
> in the RMP table.
> 2. Validate the page after its successfully added in the RMP table.
>
> To maintain the security guarantees, if the page is transitioned from
> private to shared, then perform the following before clearing the
> encryption attribute from the page table.
>
> 1. Invalidate the page.
> 2. Issue the page state change VMGEXIT to make the page shared in the
> RMP table.
>
> The early_set_memory_{encrypt,decrypt} can be called before the GHCB

s/encrypt,decrypt/encrypted,decrypted/

> is setup, use the SNP page state MSR protocol VMGEXIT defined in the GHCB
> specification to request the page state change in the RMP table.
>
> While at it, add a helper snp_prep_memory() that can be used outside
> the sev specific files to change the page state for a specified memory
> range.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

And with a few other nits below:

Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>

> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> +
> + /*
> + * Ask the hypervisor to mark the memory pages as private in the RMP
> + * table.
> + */

Indentation is off. While at it, you may want to collapse it into a one
line comment.

> + early_set_page_state(paddr, npages, SNP_PAGE_STATE_PRIVATE);
> +
> + /* Validate the memory pages after they've been added in the RMP table. */
> + pvalidate_pages(vaddr, npages, 1);
> +}
> +
> +void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
> + unsigned int npages)
> +{
> + if (!cc_platform_has(CC_ATTR_SEV_SNP))
> + return;
> +
> + /*
> + * Invalidate the memory pages before they are marked shared in the
> + * RMP table.
> + */

Collapse into one line?

> + pvalidate_pages(vaddr, npages, 0);
> +
> + /* Ask hypervisor to mark the memory pages shared in the RMP table. */

Indentation is off.

> + /*
> + * ON SNP, the page state in the RMP table must happen
> + * before the page table updates.
> + */
> + early_snp_set_memory_shared((unsigned long)__va(pa), pa, 1);

I know "1" implies "true", but to emphasize that the argument is
actually a boolean, could you please change the "1" to "true?"

> + }
> +
> /* Change the page encryption mask. */
> new_pte = pfn_pte(pfn, new_prot);
> set_pte_atomic(kpte, new_pte);
> +
> + /*
> + * If page is set encrypted in the page table, then update the RMP table to
> + * add this page as private.
> + */
> + if (enc)
> + early_snp_set_memory_private((unsigned long)__va(pa), pa, 1);

Here too, could you please change the "1" to "true?"

Venu