KVM: x86/mmu: Always pass 0 for @quadrant when gptes are 8 bytes

The quadrant is only used when gptes are 4 bytes, but
mmu_alloc_{direct,shadow}_roots() pass in a non-zero quadrant for PAE
page directories regardless. Make this less confusing by only passing in
a non-zero quadrant when it is actually necessary.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-6-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index fd1b479..f4e7978 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3389,9 +3389,10 @@ static hpa_t mmu_alloc_root(struct kvm_vcpu *vcpu, gfn_t gfn, int quadrant,
        struct kvm_mmu_page *sp;
 
        role.level = level;
+       role.quadrant = quadrant;
 
-       if (role.has_4_byte_gpte)
-               role.quadrant = quadrant;
+       WARN_ON_ONCE(quadrant && !role.has_4_byte_gpte);
+       WARN_ON_ONCE(role.direct && role.has_4_byte_gpte);
 
        sp = kvm_mmu_get_page(vcpu, gfn, role);
        ++sp->root_count;
@@ -3427,7 +3428,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
                for (i = 0; i < 4; ++i) {
                        WARN_ON_ONCE(IS_VALID_PAE_ROOT(mmu->pae_root[i]));
 
-                       root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT), i,
+                       root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT), 0,
                                              PT32_ROOT_LEVEL);
                        mmu->pae_root[i] = root | PT_PRESENT_MASK |
                                           shadow_me_value;
@@ -3512,9 +3513,8 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
        struct kvm_mmu *mmu = vcpu->arch.mmu;
        u64 pdptrs[4], pm_mask;
        gfn_t root_gfn, root_pgd;
+       int quadrant, i, r;
        hpa_t root;
-       unsigned i;
-       int r;
 
        root_pgd = mmu->get_guest_pgd(vcpu);
        root_gfn = root_pgd >> PAGE_SHIFT;
@@ -3597,7 +3597,15 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
                        root_gfn = pdptrs[i] >> PAGE_SHIFT;
                }
 
-               root = mmu_alloc_root(vcpu, root_gfn, i, PT32_ROOT_LEVEL);
+               /*
+                * If shadowing 32-bit non-PAE page tables, each PAE page
+                * directory maps one quarter of the guest's non-PAE page
+                * directory. Othwerise each PAE page direct shadows one guest
+                * PAE page directory so that quadrant should be 0.
+                */
+               quadrant = (mmu->cpu_role.base.level == PT32_ROOT_LEVEL) ? i : 0;
+
+               root = mmu_alloc_root(vcpu, root_gfn, quadrant, PT32_ROOT_LEVEL);
                mmu->pae_root[i] = root | pm_mask;
        }