From 6c6e166b2c8513721d166c74060d26d3f4aecb48 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 22 Jun 2021 00:24:54 -0700 Subject: [PATCH] KVM: x86/mmu: Don't WARN on a NULL shadow page in TDP MMU check Treat a NULL shadow page in the "is a TDP MMU" check as valid, non-TDP root. KVM uses a "direct" PAE paging MMU when TDP is disabled and the guest is running with paging disabled. In that case, root_hpa points at the pae_root page (of which only 32 bytes are used), not a standard shadow page, and the WARN fires (a lot). Fixes: 0b873fd7fb53 ("KVM: x86/mmu: Remove redundant is_tdp_mmu_enabled check") Cc: David Matlack Signed-off-by: Sean Christopherson Message-Id: <20210622072454.3449146-1-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/mmu/tdp_mmu.h | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h index b981a04..1cae448 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.h +++ b/arch/x86/kvm/mmu/tdp_mmu.h @@ -94,11 +94,13 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu) if (WARN_ON(!VALID_PAGE(hpa))) return false; + /* + * A NULL shadow page is legal when shadowing a non-paging guest with + * PAE paging, as the MMU will be direct with root_hpa pointing at the + * pae_root page, not a shadow page. + */ sp = to_shadow_page(hpa); - if (WARN_ON(!sp)) - return false; - - return is_tdp_mmu_page(sp) && sp->root_count; + return sp && is_tdp_mmu_page(sp) && sp->root_count; } #else static inline bool kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return false; } -- 2.7.4