linux-kernel - [PATCH 16/46] KVM: MMU: Discard reserved bits checking on PDE bit 7-8

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Date:	Wed, 20 May 2009 14:18:13 +0300
From:	Avi Kivity <avi@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org
Subject: [PATCH 16/46] KVM: MMU: Discard reserved bits checking on PDE bit 7-8

From: Sheng Yang <sheng@...ux.intel.com>

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@...ux.intel.com>
Signed-off-by: Avi Kivity <avi@...hat.com>
---
 arch/x86/kvm/mmu.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5baf539..409d08e 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;
 	}
-- 
1.6.0.6

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