linux-kernel - Re: [PATCH v3 2/9] KVM: nSVM: stop dereferencing vcpu->arch.mmu to get the context in kvm_init_shadow{,_npt}

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Date:   Thu, 9 Jul 2020 19:47:06 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/9] KVM: nSVM: stop dereferencing vcpu->arch.mmu to
 get the context in kvm_init_shadow{,_npt}_mmu()

On 09/07/20 16:53, Vitaly Kuznetsov wrote:
> Now as kvm_init_shadow_npt_mmu() is separated from kvm_init_shadow_mmu()
> we always know the MMU context we need to use so there is no need to
> dereference vcpu->arch.mmu pointer.
> 
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 

This is actually true of all init functions, so we can squash this in too
(my fault for being too concise):

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 2c4fb5684782..78c88e8aecfa 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4850,7 +4850,7 @@ kvm_calc_tdp_mmu_root_page_role(struct kvm_vcpu *vcpu, bool base_only)
 
 static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 {
-	struct kvm_mmu *context = vcpu->arch.mmu;
+	struct kvm_mmu *context = &vcpu->arch.root_mmu;
 	union kvm_mmu_role new_role =
 		kvm_calc_tdp_mmu_root_page_role(vcpu, false);
 
@@ -4989,7 +4989,7 @@ kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty,
 void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
 			     bool accessed_dirty, gpa_t new_eptp)
 {
-	struct kvm_mmu *context = vcpu->arch.mmu;
+	struct kvm_mmu *context = &vcpu->arch.guest_mmu;
 	u8 level = vmx_eptp_page_walk_level(new_eptp);
 	union kvm_mmu_role new_role =
 		kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty,
@@ -5023,7 +5023,7 @@ EXPORT_SYMBOL_GPL(kvm_init_shadow_ept_mmu);
 
 static void init_kvm_softmmu(struct kvm_vcpu *vcpu)
 {
-	struct kvm_mmu *context = vcpu->arch.mmu;
+	struct kvm_mmu *context = &vcpu->arch.root_mmu;
 
 	kvm_init_shadow_mmu(vcpu,
 			    kvm_read_cr0_bits(vcpu, X86_CR0_PG),


(BTW, a patch to rename nested_mmu to nested_walk_mmu and guest_mmu to
nested_tdp_mmu would be welcome).

Paolo