On Wed, Feb 09, 2022, Paolo Bonzini wrote:
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
Nit, adding () after function names helps readers easily recognize when you're
taking about a specific function, e.g. as opposed to a concept or whatever.
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
has a single root or four, because the pae_root does not have an associated
struct kvm_mmu_page.
Suggest a reword on the final paragraph, because there's a discrepancy with the
code (which handles 0, 1, or 4 "roots", versus just "single or four").
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.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
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 3c3f597ea00d..95d0fa0bb876 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3219,12 +3219,15 @@ 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);
free_active_root = (roots_to_free & KVM_MMU_ROOT_CURRENT) &&
VALID_PAGE(mmu->root.hpa);
Isn't this a separate bug fix? E.g. call kvm_mmu_unload() without a valid current
root, but with valid previous roots? In which case we'd try to free garbage, no?
