[edk2-devel] [PATCH v9 17/32] OvmfPkg/MemEncryptSevLib: add support to validate > 4GB memory in PEI phase

[Brijesh Singh via groups.io]

On 10/14/21 1:31 AM, Gerd Hoffmann wrote:
> On Wed, Oct 13, 2021 at 11:56:58AM -0500, Brijesh Singh wrote:
>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3275&data=04%7C01%7Cbrijesh.singh%40amd.com%7C82e310da29774221b2e908d98eed0a57%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637697971033546009%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=bWQoR678mAGBOGXn2UO9NdyeQocUZjj7TnpmzWp9m5U%3D&reserved=0
>>
>> The initial page built during the SEC phase is used by the
>> MemEncryptSevSnpValidateSystemRam() for the system RAM validation. The
>> page validation process requires using the PVALIDATE instruction;  the
>> instruction accepts a virtual address of the memory region that needs
>> to be validated. If hardware encounters a page table walk failure (due
>> to page-not-present) then it raises #GP.
>>
>> The initial page table built in SEC phase address up to 4GB. Add an
>> internal function to extend the page table to cover > 4GB. The function
>> builds 1GB entries in the page table for access > 4GB. This will provide
>> the support to call PVALIDATE instruction for the virtual address >
>> 4GB in PEI phase.
> I think I asked this before:  This is likewise temporary until the
> memory core can track page state and ovmf can handle lazy
> acceptance/validation of memory > 4G in DXE phase, correct?
Yes, this should go away with Lazy validation. Ah, my bad I missed your
request to document it. I will add the comment.
> Can you add a comment for that?
>
> The code looks good.
>
> take care,
>   Gerd
>


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