linux-kernel - Re: [PATCH v18 061/121] KVM: TDX: MTRR: implement get_mt

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Date: Mon, 19 Feb 2024 13:20:58 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v18 061/121] KVM: TDX: MTRR: implement get_mt_mask() for
 TDX



On 1/23/2024 7:53 AM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> Because TDX virtualize cpuid[0x1].EDX[MTRR: bit 12] to fixed 1, guest TD
> thinks MTRR is supported.  Although TDX supports only WB for private GPA,
> it's desirable to support MTRR for shared GPA.  As guest access to MTRR
> MSRs causes #VE and KVM/x86 tracks the values of MTRR MSRs, the remining

s/remining/remaining

> part is to implement get_mt_mask method for TDX for shared GPA.
>
> Pass around shared bit from kvm fault handler to get_mt_mask method so that
> it can determine if the gfn is shared or private.  Implement get_mt_mask()
> following vmx case for shared GPA and return WB for private GPA.

But the shared bit is not consumed in get_mt_mask()?

> the existing vmx_get_mt_mask() can't be directly used as CPU state(CR0.CD)
> is protected.  GFN passed to kvm_mtrr_check_gfn_range_consistency() should
> include shared bit.
>
> Suggested-by: Kai Huang <kai.huang@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/kvm/vmx/main.c    | 10 +++++++++-
>   arch/x86/kvm/vmx/tdx.c     | 23 +++++++++++++++++++++++
>   arch/x86/kvm/vmx/x86_ops.h |  2 ++
>   3 files changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 569f2f67094c..0784290d846f 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -232,6 +232,14 @@ static void vt_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
>   	vmx_load_mmu_pgd(vcpu, root_hpa, pgd_level);
>   }
>   
> +static u8 vt_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> +{
> +	if (is_td_vcpu(vcpu))
> +		return tdx_get_mt_mask(vcpu, gfn, is_mmio);
> +
> +	return vmx_get_mt_mask(vcpu, gfn, is_mmio);
> +}
> +
>   static int vt_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>   {
>   	if (!is_td(kvm))
> @@ -351,7 +359,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
>   
>   	.set_tss_addr = vmx_set_tss_addr,
>   	.set_identity_map_addr = vmx_set_identity_map_addr,
> -	.get_mt_mask = vmx_get_mt_mask,
> +	.get_mt_mask = vt_get_mt_mask,
>   
>   	.get_exit_info = vmx_get_exit_info,
>   
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 4002e7e7b191..4cbcedff4f16 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -439,6 +439,29 @@ int tdx_vm_init(struct kvm *kvm)
>   	return 0;
>   }
>   
> +u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> +{
> +	if (is_mmio)
> +		return MTRR_TYPE_UNCACHABLE << VMX_EPT_MT_EPTE_SHIFT;
> +
> +	if (!kvm_arch_has_noncoherent_dma(vcpu->kvm))
> +		return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT;
> +
> +	/*
> +	 * TDX enforces CR0.CD = 0 and KVM MTRR emulation enforces writeback.
> +	 * TODO: implement MTRR MSR emulation so that
> +	 * MTRRCap: SMRR=0: SMRR interface unsupported
> +	 *          WC=0: write combining unsupported
> +	 *          FIX=0: Fixed range registers unsupported
> +	 *          VCNT=0: number of variable range regitsers = 0
> +	 * MTRRDefType: E=1, FE=0, type=writeback only. Don't allow other value.
> +	 *              E=1: enable MTRR
> +	 *              FE=0: disable fixed range MTRRs
> +	 *              type: default memory type=writeback
> +	 */
> +	return MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT;
> +}
> +
>   int tdx_vcpu_create(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 441915e9293e..5a9aabf39c02 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -150,6 +150,7 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
>   int tdx_vcpu_create(struct kvm_vcpu *vcpu);
>   void tdx_vcpu_free(struct kvm_vcpu *vcpu);
>   void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
> +u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio);
>   
>   int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
>   
> @@ -176,6 +177,7 @@ static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOP
>   static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
>   static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
>   static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
> +static inline u8 tdx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) { return 0; }
>   
>   static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
>