[PATCH v2 06/18] KVM: x86/mmu: do not consult levels when freeing roots

Paolo Bonzini
2022-02-17T21:04:00Z

Right now, PGD caching requires a complicated dance of first computing
the MMU role and passing it to __kvm_mmu_new_pgd(), and then separately calling
kvm_init_mmu().

Part of this is due to kvm_mmu_free_roots using mmu->root_level and
mmu->shadow_root_level to distinguish whether the page table uses a single
root or 4 PAE roots. Because kvm_init_mmu() can overwrite mmu->root_level,
kvm_mmu_free_roots() must be called before kvm_init_mmu().

However, even after kvm_init_mmu() there is a way to detect whether the
page table may hold PAE roots, as root.hpa isn't backed by a shadow when
it points at PAE roots. Using this method results in simpler code, and
is one less obstacle in moving all calls to __kvm_mmu_new_pgd() after the
MMU has been initialized.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu/mmu.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a478667d7561..e1578f71feae 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3240,12 +3240,15 @@ void kvm_mmu_free_roots(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
struct kvm *kvm = vcpu->kvm;
int i;
LIST_HEAD(invalid_list);
- bool free_active_root = roots_to_free & KVM_MMU_ROOT_CURRENT;
+ bool free_active_root;

BUILD_BUG_ON(KVM_MMU_NUM_PREV_ROOTS >= BITS_PER_LONG);

/* Before acquiring the MMU lock, see if we need to do any real work. */
- if (!(free_active_root && VALID_PAGE(mmu->root.hpa))) {
+ free_active_root = (roots_to_free & KVM_MMU_ROOT_CURRENT)
+ && VALID_PAGE(mmu->root.hpa);
+
+ if (!free_active_root) {
for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
if ((roots_to_free & KVM_MMU_ROOT_PREVIOUS(i)) &&
VALID_PAGE(mmu->prev_roots[i].hpa))
@@ -3263,8 +3266,7 @@ void kvm_mmu_free_roots(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
&invalid_list);

if (free_active_root) {
- if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL &&
- (mmu->root_level >= PT64_ROOT_4LEVEL || mmu->direct_map)) {
+ if (to_shadow_page(mmu->root.hpa)) {
mmu_free_root_page(kvm, &mmu->root.hpa, &invalid_list);
} else if (mmu->pae_root) {
for (i = 0; i < 4; ++i) {
--
2.31.1