Always free obsolete roots when pre-faulting SPTEs in case it's called after a root is invalidated (e.g., by memslot removal) but before any vcpu_enter_guest() processing of KVM_REQ_MMU_FREE_OBSOLETE_ROOTS. Lack of kvm_mmu_free_obsolete_roots() in this scenario can lead to kvm_mmu_reload() failing to load a new root if the current root hpa is an obsolete root (which is not INVALID_PAGE). Consequently, kvm_arch_vcpu_pre_fault_memory() will retry infinitely due to the checking of is_page_fault_stale(). It's safe to call kvm_mmu_free_obsolete_roots() even if there are no obsolete roots or if it's called a second time when vcpu_enter_guest() later processes KVM_REQ_MMU_FREE_OBSOLETE_ROOTS. This is because kvm_mmu_free_obsolete_roots() sets an obsolete root to INVALID_PAGE and will do nothing to an INVALID_PAGE. Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx> --- arch/x86/kvm/mmu/mmu.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 47fd3712afe6..72f68458049a 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4740,7 +4740,12 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, /* * reload is efficient when called repeatedly, so we can do it on * every iteration. + * Before reload, free obsolete roots in case the prefault is called + * after a root is invalidated (e.g., by memslot removal) but + * before any vcpu_enter_guest() processing of + * KVM_REQ_MMU_FREE_OBSOLETE_ROOTS. */ + kvm_mmu_free_obsolete_roots(vcpu); r = kvm_mmu_reload(vcpu); if (r) return r; -- 2.43.2
