Re: [PATCH 03/22] KVM: x86/mmu: adjust MMIO generation bit allocation and allowed mask

[Paolo Bonzini]

On 3/24/26 04:48, Huang, Kai wrote:
> >   /*
> > - * Due to limited space in PTEs, the MMIO generation is a 19 bit subset of
> > + * Due to limited space in PTEs, the MMIO generation is an 18 bit subset of
> >    * the memslots generation and is derived as follows:
>
> Is "a -> an" unintentional change?

No, "a nineteen-bit" -> "an eighteen-bit". :)

> Besides the changes to MMIO_GEN, the FROZEN_SPTE seems to have bit 10 set:
>
>      #define FROZEN_SPTE (SHADOW_NONPRESENT_VALUE | 0x5a0ULL)
>
> When MBEC is enabled, IIUC such SPTE will be treated as present by hardware
> if CPU supports execution-only SPTE.
>
> Also, when MBEC is enabled, per SDM if CPU doesn't support execution-only,
> an SPTE with bit 0 clear but with bit 10 set will trigger EPT
> miscofiguration, rather than EPT violation.
>
> So seems we should exclude bit 10 from FROZEN_SPTE.

True, good catch (so 0x5a0 should become 0x1a0).

Paolo