[PATCH v5 04/21] KVM: x86/mmu: Always pass 0 for @quadrant when gptes are 8 bytes

[David Matlack]

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 at google.com>
---
 arch/x86/kvm/mmu/mmu.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a927a062a598..34786244ebad 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3409,9 +3409,10 @@ static hpa_t mmu_alloc_root(struct kvm_vcpu *vcpu, gfn_t gfn, int quadrant,
 	role.level = level;
 	role.direct = direct;
 	role.access = ACC_ALL;
+	role.quadrant = quadrant;
 
-	if (role.has_4_byte_gpte)
-		role.quadrant = quadrant;
+	WARN_ON_ONCE(quadrant && !role.has_4_byte_gpte);
+	WARN_ON_ONCE(direct && role.has_4_byte_gpte);
 
 	if (level <= vcpu->arch.mmu->cpu_role.base.level)
 		role.passthrough = 0;
@@ -3450,7 +3451,7 @@ 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, true);
 			mmu->pae_root[i] = root | PT_PRESENT_MASK |
 					   shadow_me_mask;
@@ -3535,6 +3536,7 @@ 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;
+	unsigned int quadrant;
 	hpa_t root;
 	unsigned i;
 	int r;
@@ -3620,7 +3622,15 @@ 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, false);
+		/*
+		 * 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, false);
 		mmu->pae_root[i] = root | pm_mask;
 	}
 
-- 
2.36.0.550.gb090851708-goog