[PATCH 1/8] KVM: x86: #PF error-code on R/W operations is wrong

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When emulating an instruction that reads the destination memory operand (i.e.,
instructions without the Mov flag in the emulator), the operand is first read.
If a page-fault is detected in this phase, the error-code which would be
delivered to the VM does not indicate that the access that caused the exception
is a write one. This does not conform with real hardware, and may cause the VM
to enter the page-fault handler twice for no reason (once for read, once for
write).

Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 12 ++++++++++++
 arch/x86/kvm/emulate.c          |  6 +++++-
 arch/x86/kvm/mmu.h              | 12 ------------
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 73ccb12..d6f90ca 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -162,6 +162,18 @@ enum {
 #define DR7_FIXED_1	0x00000400
 #define DR7_VOLATILE	0xffff2bff
 
+#define PFERR_PRESENT_BIT 0
+#define PFERR_WRITE_BIT 1
+#define PFERR_USER_BIT 2
+#define PFERR_RSVD_BIT 3
+#define PFERR_FETCH_BIT 4
+
+#define PFERR_PRESENT_MASK (1U << PFERR_PRESENT_BIT)
+#define PFERR_WRITE_MASK (1U << PFERR_WRITE_BIT)
+#define PFERR_USER_MASK (1U << PFERR_USER_BIT)
+#define PFERR_RSVD_MASK (1U << PFERR_RSVD_BIT)
+#define PFERR_FETCH_MASK (1U << PFERR_FETCH_BIT)
+
 /* apic attention bits */
 #define KVM_APIC_CHECK_VAPIC	0
 /*
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 7a9697f..e5a84be 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4941,8 +4941,12 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
 		/* optimisation - avoid slow emulated read if Mov */
 		rc = segmented_read(ctxt, ctxt->dst.addr.mem,
 				   &ctxt->dst.val, ctxt->dst.bytes);
-		if (rc != X86EMUL_CONTINUE)
+		if (rc != X86EMUL_CONTINUE) {
+			if (rc == X86EMUL_PROPAGATE_FAULT &&
+			    ctxt->exception.vector == PF_VECTOR)
+				ctxt->exception.error_code |= PFERR_WRITE_MASK;
 			goto done;
+		}
 	}
 	ctxt->dst.orig_val = ctxt->dst.val;
 
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 6b34876b..daae711 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -44,18 +44,6 @@
 #define PT_DIRECTORY_LEVEL 2
 #define PT_PAGE_TABLE_LEVEL 1
 
-#define PFERR_PRESENT_BIT 0
-#define PFERR_WRITE_BIT 1
-#define PFERR_USER_BIT 2
-#define PFERR_RSVD_BIT 3
-#define PFERR_FETCH_BIT 4
-
-#define PFERR_PRESENT_MASK (1U << PFERR_PRESENT_BIT)
-#define PFERR_WRITE_MASK (1U << PFERR_WRITE_BIT)
-#define PFERR_USER_MASK (1U << PFERR_USER_BIT)
-#define PFERR_RSVD_MASK (1U << PFERR_RSVD_BIT)
-#define PFERR_FETCH_MASK (1U << PFERR_FETCH_BIT)
-
 static inline u64 rsvd_bits(int s, int e)
 {
 	return ((1ULL << (e - s + 1)) - 1) << s;
-- 
1.9.1

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