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

David Matlack
2022-05-13T20:28:43Z

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>
---
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