linux-kernel - Re: [PATCH v18 063/121] KVM: x86/mmu: Introduce kvm_mmu_map_tdp

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Message-ID: <CAAhR5DEpX1AMQ1EwFB9TsvRufZ5Cwvpx2u9xGtXU5gbQA67fxg@mail.gmail.com>
Date: Tue, 6 Feb 2024 11:26:07 -0800
From: Sagi Shahar <sagis@...gle.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>, Kai Huang <kai.huang@...el.com>, chen.bo@...el.com, 
	hang.yuan@...el.com, tina.zhang@...el.com, 
	Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v18 063/121] KVM: x86/mmu: Introduce kvm_mmu_map_tdp_page()
 for use by TDX

On Mon, Jan 22, 2024 at 3:56 PM <isaku.yamahata@...el.com> wrote:
>
> From: Sean Christopherson <sean.j.christopherson@...el.com>
>
> Introduce a helper to directly (pun intended) fault-in a TDP page
> without having to go through the full page fault path.  This allows
> TDX to get the resulting pfn and also allows the RET_PF_* enums to
> stay in mmu.c where they belong.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> v14 -> v15:
> - Remove loop in kvm_mmu_map_tdp_page() and return error code based on
>   RET_FP_xxx value to avoid potential infinite loop.  The caller should
>   loop on -EAGAIN instead now.
> ---
>  arch/x86/kvm/mmu.h     |  3 +++
>  arch/x86/kvm/mmu/mmu.c | 57 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 60 insertions(+)
>
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index bad6a1e43a54..ebf91b605c37 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -184,6 +184,9 @@ static inline void kvm_mmu_refresh_passthrough_bits(struct kvm_vcpu *vcpu,
>         __kvm_mmu_refresh_passthrough_bits(vcpu, mmu);
>  }
>
> +int kvm_mmu_map_tdp_page(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code,
> +                        int max_level);
> +
>  /*
>   * Check if a given access (described through the I/D, W/R and U/S bits of a
>   * page fault error code pfec) causes a permission fault with the given PTE
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 7db152f46d82..26d215e85b76 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4635,6 +4635,63 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>         return direct_page_fault(vcpu, fault);
>  }
>
> +int kvm_mmu_map_tdp_page(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code,
> +                        int max_level)
> +{
> +       int r;
> +       struct kvm_page_fault fault = (struct kvm_page_fault) {
> +               .addr = gpa,
> +               .error_code = error_code,
> +               .exec = error_code & PFERR_FETCH_MASK,
> +               .write = error_code & PFERR_WRITE_MASK,
> +               .present = error_code & PFERR_PRESENT_MASK,
> +               .rsvd = error_code & PFERR_RSVD_MASK,
> +               .user = error_code & PFERR_USER_MASK,
> +               .prefetch = false,
> +               .is_tdp = true,
> +               .is_private = error_code & PFERR_GUEST_ENC_MASK,
> +               .nx_huge_page_workaround_enabled = is_nx_huge_page_enabled(vcpu->kvm),
> +       };
> +
> +       WARN_ON_ONCE(!vcpu->arch.mmu->root_role.direct);
> +       fault.gfn = gpa_to_gfn(fault.addr) & ~kvm_gfn_shared_mask(vcpu->kvm);
> +       fault.slot = kvm_vcpu_gfn_to_memslot(vcpu, fault.gfn);
> +
> +       r = mmu_topup_memory_caches(vcpu, false);
> +       if (r)
> +               return r;
> +
> +       fault.max_level = max_level;
> +       fault.req_level = PG_LEVEL_4K;
> +       fault.goal_level = PG_LEVEL_4K;
> +
> +#ifdef CONFIG_X86_64
> +       if (tdp_mmu_enabled)
> +               r = kvm_tdp_mmu_page_fault(vcpu, &fault);
> +       else
> +#endif
> +               r = direct_page_fault(vcpu, &fault);

Are we ever going to hit the direct_page_fault case? I thought TDX
only supported tdp_mmu?

> +
> +       if (is_error_noslot_pfn(fault.pfn) || vcpu->kvm->vm_bugged)
> +               return -EFAULT;
> +
> +       switch (r) {
> +       case RET_PF_RETRY:
> +               return -EAGAIN;
> +
> +       case RET_PF_FIXED:
> +       case RET_PF_SPURIOUS:
> +               return 0;
> +
> +       case RET_PF_CONTINUE:
> +       case RET_PF_EMULATE:
> +       case RET_PF_INVALID:
> +       default:
> +               return -EIO;
> +       }
> +}
> +EXPORT_SYMBOL_GPL(kvm_mmu_map_tdp_page);
> +
>  static void nonpaging_init_context(struct kvm_mmu *context)
>  {
>         context->page_fault = nonpaging_page_fault;
> --
> 2.25.1
>