Commit c205fb7d authored by Nadav Amit's avatar Nadav Amit Committed by Paolo Bonzini
Browse files

KVM: x86: #PF error-code on R/W operations is wrong 



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: default avatarNadav Amit <namit@cs.technion.ac.il>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 7e71a59b

arch/x86/include/asm/kvm_host.h

+12 −0
Original line number Diff line number Diff line
@@ -160,6 +160,18 @@ 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

/*

arch/x86/kvm/emulate.c

+5 −1
Original line number Diff line number Diff line
@@ -4909,9 +4909,13 @@ 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;



special_insn:

arch/x86/kvm/mmu.h

+0 −12
Original line number Diff line number Diff line
@@ -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;

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