Feng <feng.wu@xxxxxxxxx> wrote: > > >> -----Original Message----- >> From: kvm-owner@xxxxxxxxxxxxxxx [mailto:kvm-owner@xxxxxxxxxxxxxxx] On >> Behalf Of Nadav Amit >> Sent: Thursday, December 25, 2014 8:52 AM >> To: pbonzini@xxxxxxxxxx >> Cc: kvm@xxxxxxxxxxxxxxx; Nadav Amit >> Subject: [PATCH 1/8] 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: 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); > > This is a write operation, do you know why we need to read the dst operand first here? Some x86 instructions read the destination operand during their operation. For instance - "MOV [EAX], EBX" (Intel ASM format), would perform [EAX] = [EAX] + EBX. Therefore, it would first read the memory of [EAX] at this stage. Nadav -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
