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

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Date:   Thu, 17 Feb 2022 16:03:28 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     seanjc@...gle.com
Subject: [PATCH v2 06/18] KVM: x86/mmu: do not consult levels when freeing roots

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@...hat.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