On 22/06/21 09:24, Sean Christopherson wrote:
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 <dmatlack@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/tdp_mmu.h | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
Queued, thanks.
Paolo
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index b981a044ab55..1cae4485b3bc 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; }
