KVM: MMU: Discard reserved bits checking on PDE bit 7-8

1. It's related to a Linux kernel bug which fixed by Ingo on
07a66d7c53a538e1a9759954a82bb6c07365eff9. The original code exists for quite a
long time, and it would convert a PDE for large page into a normal PDE. But it
fail to fit normal PDE well.  With the code before Ingo's fix, the kernel would
fall reserved bit checking with bit 8 - the remaining global bit of PTE. So the
kernel would receive a double-fault.

2. After discussion, we decide to discard PDE bit 7-8 reserved checking for now.
For this marked as reserved in SDM, but didn't checked by the processor in
fact...

Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index da3ad3cf314..b582adde683 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2194,7 +2194,7 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, int level)
                         rsvd_bits(maxphyaddr, 63) |
                         rsvd_bits(7, 8) | rsvd_bits(1, 2);      /* PDPTE */
                 context->rsvd_bits_mask[0][1] = exb_bit_rsvd |
-                        rsvd_bits(maxphyaddr, 62);              /* PDE */
+                        rsvd_bits(maxphyaddr, 62);      /* PDE */
                 context->rsvd_bits_mask[0][0] = exb_bit_rsvd |
                         rsvd_bits(maxphyaddr, 62);      /* PTE */
                 context->rsvd_bits_mask[1][1] = exb_bit_rsvd |
@@ -2208,13 +2208,14 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, int level)
                 context->rsvd_bits_mask[0][2] = exb_bit_rsvd |
                         rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
                 context->rsvd_bits_mask[0][1] = exb_bit_rsvd |
-                        rsvd_bits(maxphyaddr, 51) | rsvd_bits(7, 8);
+                        rsvd_bits(maxphyaddr, 51);
                 context->rsvd_bits_mask[0][0] = exb_bit_rsvd |
                         rsvd_bits(maxphyaddr, 51);
                 context->rsvd_bits_mask[1][3] = context->rsvd_bits_mask[0][3];
                 context->rsvd_bits_mask[1][2] = context->rsvd_bits_mask[0][2];
                 context->rsvd_bits_mask[1][1] = exb_bit_rsvd |
-                        rsvd_bits(maxphyaddr, 51) | rsvd_bits(13, 20);
+                        rsvd_bits(maxphyaddr, 51) |
+                        rsvd_bits(13, 20);              /* large page */
                 context->rsvd_bits_mask[1][0] = ~0ull;
                 break;
         }