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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@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Nadav Amit 2014-12-25 02:52:16 +02:00 committed by Paolo Bonzini
parent 7e71a59b25
commit c205fb7d7d
3 changed files with 17 additions and 13 deletions
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12
arch/x86/include/asm/kvm_host.h
View File

@ -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
/*

6
arch/x86/kvm/emulate.c
View File

@ -4909,8 +4909,12 @@ 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;

12
arch/x86/kvm/mmu.h
View File

@ -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;