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

PATCH Applied Sheng Yang 2 participants 2 messages Apr 2, 2009

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x86 KVM KVM x86
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Sheng Yang

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PATCH 1/1 KVM: 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 <[email protected]>
---
 arch/x86/kvm/mmu.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)
arch/x86/kvm/mmu.c +4 -3
index e0f63b6..a0b130d 100644
@@ -2196,7 +2196,7 @@ static void reset_rsvds_bits_mask(struct kvm_vcpu *vcpu, int level)
 		break;
 	case PT32E_ROOT_LEVEL:
 		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 |

@@ -2210,13 +2210,14 @@ 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;
 	}
Signature · 1 line
1.5.4.5
Applied
#1 lore raw
Quoted 11 lines · Sheng Yang

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...

Applied, thanks.

Signature · 1 line
error compiling committee.c: too many arguments to function