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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: 0b873fd7fb ("KVM: x86/mmu: Remove redundant is_tdp_mmu_enabled check")
Cc: David Matlack <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622072454.3449146-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-06-22 00:24:54 -07:00 committed by Paolo Bonzini
parent ef6a74b2e5
commit 6c6e166b2c
1 changed files with 6 additions and 4 deletions
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10
arch/x86/kvm/mmu/tdp_mmu.h
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@ -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; }