linux-kernel - Re: [PATCH v19 016/130] KVM: x86/mmu: Introduce kvm_mmu_map_tdp

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Date: Wed, 6 Mar 2024 14:22:34 -0800
From: Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: isaku.yamahata@...el.com, 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,
	Sean Christopherson <sean.j.christopherson@...el.com>,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 016/130] KVM: x86/mmu: Introduce
 kvm_mmu_map_tdp_page() for use by TDX

On Wed, Mar 06, 2024 at 03:13:22PM +0800,
Binbin Wu <binbin.wu@...ux.intel.com> wrote:

> 
> 
> On 2/26/2024 4:25 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>
> > ---
> > v19:
> > - Move up for KVM_MEMORY_MAPPING.
> > - Add goal_level for the caller to know how many pages are mapped.
> > 
> > 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.
> > 
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> > ---
> >   arch/x86/kvm/mmu.h     |  3 +++
> >   arch/x86/kvm/mmu/mmu.c | 58 ++++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 61 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> > index 60f21bb4c27b..d96c93a25b3b 100644
> > --- a/arch/x86/kvm/mmu.h
> > +++ b/arch/x86/kvm/mmu.h
> > @@ -183,6 +183,9 @@ 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,
> > +			 u8 max_level, u8 *goal_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 61674d6b17aa..ca0c91f14063 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4615,6 +4615,64 @@ 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,
> > +			 u8 max_level, u8 *goal_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.slot = kvm_vcpu_gfn_to_memslot(vcpu, fault.gfn);
> > +
> > +	r = mmu_topup_memory_caches(vcpu, false);
> 
> Does it need a cache topup here?
> Both kvm_tdp_mmu_page_fault() and direct_page_fault() will call
> mmu_topup_memory_caches() when needed.

You're right. As the called function has changed, I missed to remove it.
-- 
Isaku Yamahata <isaku.yamahata@...ux.intel.com>