Re: [PATCH v8 15/40] x86/mm: Add support to validate memory when changing C-bit

Venu Busireddy
2022-01-04T22:32:26Z

On 2021-12-10 09:43:07 -0600, Brijesh Singh wrote:
> The set_memory_{encrypt,decrypt}() are used for changing the pages

s/set_memory_{encrypt,decrypt}/snp_set_memory_{shared,private}/

> 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 memory region in
> the RMP table.
> 2. Validate the memory region after the RMP entry is added.
>
> To maintain the security guarantees, if the page is transitioned from
> private to shared, then perform the following before encryption attribute
> is removed from the page table:
>
> 1. Invalidate the page.
> 2. Issue the page state change VMGEXIT to remove the page from RMP table.
>
> To change the page state in the RMP table, use the Page State Change
> VMGEXIT defined in the GHCB specification.
>
> The GHCB specification provides the flexibility to use either 4K or 2MB
> page size in during the page state change (PSC) request. For now use the
> 4K page size for all the PSC until page size tracking is supported in the
> kernel.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

[snip]

> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 2971aa280ce6..35c772bf9f6c 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -574,7 +574,7 @@ static void pvalidate_pages(unsigned long vaddr, unsigned int npages, bool valid
> }
> }
>
> -static void __init early_set_page_state(unsigned long paddr, unsigned int npages, enum psc_op op)
> +static void __init early_set_pages_state(unsigned long paddr, unsigned int npages, enum psc_op op)

Is there a need to change the name? "npages" can take a value of 1 too.
Hence, early_set_page_state() appears to be a better name!

> + /*
> + * Page State Change VMGEXIT can pass error code through
> + * exit_info_2.
> + */

Collapse into one line?

> +void snp_set_memory_shared(unsigned long vaddr, unsigned int npages)
> +{
> + if (!cc_platform_has(CC_ATTR_SEV_SNP))
> + return;
> +
> + pvalidate_pages(vaddr, npages, 0);

Replace '0' with "false"?

> +
> + set_pages_state(vaddr, npages, SNP_PAGE_STATE_SHARED);
> +}
> +
> +void snp_set_memory_private(unsigned long vaddr, unsigned int npages)
> +{
> + if (!cc_platform_has(CC_ATTR_SEV_SNP))
> + return;
> +
> + set_pages_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE);
> +
> + pvalidate_pages(vaddr, npages, 1);

Replace '1' with "true"?

Venu