Re: [PATCH 03/28] KVM: x86/mmu: free up bit 10 of PTEs in preparation for MBEC

Sean Christopherson
2026-04-30T18:05:01Z

On Thu, Apr 30, 2026, Paolo Bonzini wrote:
> From: Jon Kohler <jon@nutanix.com>
>
> Update SPTE_MMIO_ALLOWED_MASK to allow EPT user executable (bit 10) to
> be treated like EPT RWX bit2:0, as when mode-based execute control is
> enabled, bit 10 can act like a "present" bit.

For posterity, this matters because MMIO SPTEs for TDX need to be RWX=0 in order
to generate #VEs on any access (hardware never reflects EPT Misconfigs as #VEs).
Arguably we could delay this until the TDX-Module enables MBEC (or maybe that's
already in the works?), because even though KVM enables MBEC, that only matters
for non-TDX guests.

But I don't see any point in delaying the inevitable.