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SubjectRe: [PATCH Part2 RFC v4 33/40] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT
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On 7/19/21 1:55 PM, Sean Christopherson wrote:
>
> I've no objection to using PSC for enums and whatnot, and I'll happily defer to
> Boris for functions in the core kernel and guest, but for KVM I'd really like to
> spell out the name for the two or so main handler functions.

Noted.


>>
>> Maybe I am missing something, I am not able to follow 'guest won't be able
>> to convert a 2mb chunk back to a 2mb large page'. The page-size used inside
>> the guest have to relationship with the RMP/NPT page-size. e.g, a guest can
>> validate the page range as a 4k and still map the page range as a 2mb or 1gb
>> in its pagetable.
>
> The proposed code walks KVM's TDP and adjusts the RMP level to be the min of the
> guest+host levels. Once KVM has installed a 4kb TDP SPTE, that walk will find
> the 4kb TDP SPTE and thus operate on the RMP at a 4kb granularity. To allow full
> restoration of 2mb PTE+SPTE+RMP, KVM needs to zap the 4kb SPTE(s) at some point
> to allow rebuilding a 2mb SPTE.
>

Ah I see. In that case, SNP firmware provides a command
"SNP_PAGE_UNMASH" that can be used by the hypervisor to combines the
multiple 4k entry into a single 2mb without affecting the validation.

-Brijesh

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