KVM: MMU: Fix 32 bit legacy paging with NPT

This patch fixes 32 bit legacy paging with NPT enabled. The
mmu_check_root call on the top-level of the loop causes
root_gfn to take values (in the tdp_enabled path) which are
outside of guest memory. So the mmu_check_root call fails at
some point in the loop interation causing the guest to
tiple-fault.
This patch changes the mmu_check_root calls to the places
where they are really necessary. As a side-effect it
introduces a check for the root of a pae page table too.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d2dad65a45f8..b2136f921d7e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2387,6 +2387,10 @@ static int mmu_alloc_roots(struct kvm_vcpu *vcpu)
                 return 0;
         }
         direct = !is_paging(vcpu);
+
+        if (mmu_check_root(vcpu, root_gfn))
+                return 1;
+
         for (i = 0; i < 4; ++i) {
                 hpa_t root = vcpu->arch.mmu.pae_root[i];
 
@@ -2398,10 +2402,10 @@ static int mmu_alloc_roots(struct kvm_vcpu *vcpu)
                                 continue;
                         }
                         root_gfn = pdptr >> PAGE_SHIFT;
+                        if (mmu_check_root(vcpu, root_gfn))
+                                return 1;
                 } else if (vcpu->arch.mmu.root_level == 0)
                         root_gfn = 0;
-                if (mmu_check_root(vcpu, root_gfn))
-                        return 1;
                 if (tdp_enabled) {
                         direct = 1;
                         root_gfn = i << 30;