Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section shared in RMP table

Brijesh Singh
2022-01-05T19:52:21Z

On 1/4/22 11:56 AM, Venu Busireddy wrote:
> On 2021-12-10 09:43:05 -0600, Brijesh Singh wrote:
>> The encryption attribute for the bss.decrypted region is cleared in the
>> initial page table build. This is because the section contains the data
>> that need to be shared between the guest and the hypervisor.
>>
>> When SEV-SNP is active, just clearing the encryption attribute in the
>> page table is not enough. The page state need to be updated in the RMP
>> table.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>> arch/x86/kernel/head64.c | 7 +++++++
>> 1 file changed, 7 insertions(+)
>>
>> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
>> index fa02402dcb9b..72c5082a3ba4 100644
>> --- a/arch/x86/kernel/head64.c
>> +++ b/arch/x86/kernel/head64.c
>> @@ -143,7 +143,14 @@ static unsigned long sme_postprocess_startup(struct boot_params *bp, pmdval_t *p
>> if (sme_get_me_mask()) {
>> vaddr = (unsigned long)__start_bss_decrypted;
>> vaddr_end = (unsigned long)__end_bss_decrypted;
>> +
>> for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
>> + /*
>> + * When SEV-SNP is active then transition the page to shared in the RMP
>> + * table so that it is consistent with the page table attribute change.
>> + */
>> + early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), PTRS_PER_PMD);
>
> Shouldn't the first argument be vaddr as below?
>

Nope, sme_postprocess_startup() is called while we are fixing the
initial page table and running with identity mapping (so va == pa).

thanks

> early_snp_set_memory_shared(vaddr, __pa(vaddr), PTRS_PER_PMD);
>
> Venu
>