linux-kernel - Re: [PATCH v10 034/108] KVM: x86/mmu: Add Suppress VE bit to shadow_mmio

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Date:   Wed, 9 Nov 2022 11:48:30 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v10 034/108] KVM: x86/mmu: Add Suppress VE bit to
 shadow_mmio_{value, mask}

On Sat, 2022-10-29 at 23:22 -0700, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Because TDX will need shadow_mmio_mask to be VMX_SUPPRESS_VE | RWX	
> shadow_mmio_value to be 0, make VMX EPT case use same value for TDX
> shadow_mmio_mask.  
> 

TDX need to use different mmio_mask/value doesn't mean they need to be changed
for VMX guest.  I think the true purpose here is to still be able to use a
global shadow_mmio_mask for both TDX and VMX guests.  So please explicitly call
out.  


> For VMX, VMX_SUPPRESS_VE doesn't matter, it doesn't
> affect VMX logic to add the bit to shadow_mmio_{value, mask}.  Note that
> shadow_mmio_value will be per-VM value.

Not sure why the last sentence matters.

> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/kvm/mmu/spte.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index 0b97a045c5f0..5d5c06d4fd89 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -437,8 +437,8 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
>  	 * EPT Misconfigurations are generated if the value of bits 2:0
>  	 * 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);
> +	kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE | VMX_EPT_SUPPRESS_VE_BIT,

Is "suppress #VE" bit required for mmio_value for VMX guest? Why adding it?

> +				   VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0);
>  }
>  EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);
>