[PATCH 13/18] KVM: x86/mmu: Process only valid TDP MMU roots when aging a gfn range

Sean Christopherson
2024-10-11T02:11:19Z

Skip invalid TDP MMU roots when aging a gfn range. There is zero reason
to process invalid roots, as they by definition hold stale information.
E.g. if a root is invalid because its from a previous memslot generation,
in the unlikely event the root has a SPTE for the gfn, then odds are good
that the gfn=>hva mapping is different, i.e. doesn't map to the hva that
is being aged by the primary MMU.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/tdp_mmu.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index f77927b57962..e8c061bf94ec 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1205,9 +1205,11 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,

/*
* Don't support rescheduling, none of the MMU notifiers that funnel
- * into this helper allow blocking; it'd be dead, wasteful code.
+ * into this helper allow blocking; it'd be dead, wasteful code. Note,
+ * this helper must NOT be used to unmap GFNs, as it processes only
+ * valid roots!
*/
- for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
+ for_each_valid_tdp_mmu_root(kvm, root, range->slot->as_id) {
rcu_read_lock();

tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
--
2.47.0.rc1.288.g06298d1525-goog