linux-kernel - Re: [PATCH 06/21] KVM: x86/mmu: Track shadow MMIO value on a per-VM basis

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Date: Fri, 1 Mar 2024 15:44:42 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
 kvm@...r.kernel.org
Cc: seanjc@...gle.com, michael.roth@....com, isaku.yamahata@...el.com,
 thomas.lendacky@....com
Subject: Re: [PATCH 06/21] KVM: x86/mmu: Track shadow MMIO value on a per-VM
 basis

On 2/28/2024 7:20 AM, Paolo Bonzini wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> TDX will use a different shadow PTE entry value for MMIO from VMX.  Add
> members to kvm_arch and track value for MMIO per-VM instead of global
> variables.  By using the per-VM EPT entry value for MMIO, the existing VMX
> logic is kept working.  Introduce a separate setter function so that guest
> TD can override later.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Message-Id: <229a18434e5d83f45b1fcd7bf1544d79db1becb6.1705965635.git.isaku.yamahata@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>   arch/x86/include/asm/kvm_host.h |  2 ++
>   arch/x86/kvm/mmu.h              |  1 +
>   arch/x86/kvm/mmu/mmu.c          |  8 +++++---
>   arch/x86/kvm/mmu/spte.c         | 10 ++++++++--
>   arch/x86/kvm/mmu/spte.h         |  4 ++--
>   arch/x86/kvm/mmu/tdp_mmu.c      |  6 +++---
>   6 files changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 85dc0f7d09e3..a4514c2ef0ec 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1313,6 +1313,8 @@ struct kvm_arch {
>   	 */
>   	spinlock_t mmu_unsync_pages_lock;
>   
> +	u64 shadow_mmio_value;
> +
>   	struct iommu_domain *iommu_domain;
>   	bool iommu_noncoherent;
>   #define __KVM_HAVE_ARCH_NONCOHERENT_DMA
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 60f21bb4c27b..2c54ba5b0a28 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -101,6 +101,7 @@ static inline u8 kvm_get_shadow_phys_bits(void)
>   }
>   
>   void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask);
> +void kvm_mmu_set_mmio_spte_value(struct kvm *kvm, u64 mmio_value);

Now, the new added function along with above function mislead people on 
their names. It's easily to think

  - kvm_mmu_set_mmio_spte_mask() is to set shadow_mmio_mask, while
  - kvm_mmu_set_mmio_spte_value() is to set shadow_mmio_value

we'd better come up with a better name.

Other than it, the patch looks good to me.

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>