Re: [PATCH v11 032/113] KVM: x86/mmu: Add Suppress VE bit to shadow_mmio_mask

[Huang, Kai]

On Thu, 2023-01-12 at 08:31 -0800, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> To make use of the same value of shadow_mmio_mask for TDX and VMX, add
> Suppress-VE bit to shadow_mmio_mask so that shadow_mmio_mask can be common
> for both VMX and TDX.
> 
> TDX will need shadow_mmio_mask to be VMX_SUPPRESS_VE | RWX and
> shadow_mmio_value to be 0 so that EPT violation is triggered.  For VMX,
> VMX_SUPPRESS_VE doesn't matter because the spte value is required to cause
> EPT misconfig.  the additional bit doesn't affect VMX logic to add the bit
> to shadow_mmio_{value, mask}.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>  arch/x86/kvm/mmu/spte.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index fce6f047399f..cc0bc058fb25 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -431,7 +431,9 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
>  	shadow_dirty_mask	= has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
>  	shadow_nx_mask		= 0ull;
>  	shadow_x_mask		= VMX_EPT_EXECUTABLE_MASK;
> -	shadow_present_mask	= has_exec_only ? 0ull : VMX_EPT_READABLE_MASK;
> +	/* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */
> +	shadow_present_mask	=
> +		(has_exec_only ? 0ull : VMX_EPT_READABLE_MASK) | VMX_EPT_SUPPRESS_VE_BIT;

This chunk has nothing to do with what this patch claims to do.

>  	/*
>  	 * EPT overrides the host MTRRs, and so KVM must program the desired
>  	 * memtype directly into the SPTEs.  Note, this mask is just the mask
> @@ -448,7 +450,7 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
>  	 * of an EPT paging-structure entry is 110b (write/execute).
>  	 */
>  	kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE,
> -				   VMX_EPT_RWX_MASK, 0);
> +				   VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0);
>  }
>  EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);
>