From: Avi Kivity <avi@redhat.com>
To: Matteo <signorinimatteo@gmail.com>
Cc: kvm@vger.kernel.org
Subject: Re: X86EMUL_PROPAGATE_FAULT
Date: Mon, 09 May 2011 11:50:24 +0300 [thread overview]
Message-ID: <4DC7AAD0.1070709@redhat.com> (raw)
In-Reply-To: <4DC2BCAC.8060703@gmail.com>
On 05/05/2011 06:05 PM, Matteo wrote:
> Hello to everybody,
>
> I am working on KVM version 2.6.38
> and I'm facing a new problem on an emulated instruction
> whose implementation is already in kvm.
>
> The error shows up after the emulation of the "RET" opcode (C3 Byte
> Opcode).
> When trying to emulate the instruction
> at the address loaded after the pop instruction made by the RET
> I get an X86EMUL_PROPAGATE_FAULT error due to a gpa == UNMAPPED_GVA
> as you can see in the following debug trace:
>
> ---------------8<-------------------------------------------------
> x86_decode_insn:2705 -> Starting New Instruction Decode
>
> x86_decode_insn:2709 -> c->eip = ctxt->eip = 3226138255
> x86_decode_insn:2759 -> Opcode -> c3
> x86_decode_insn:2928 -> Decode and fetch the source operand
> x86_decode_insn:2931 -> SrcNone
> x86_decode_insn:3015 -> Decode and fetch the second source operand
> x86_decode_insn:3018 -> Src2None
> x86_decode_insn:3044 -> Decode and fetch the destination operand
> x86_decode_insn:3089 -> ImplicitOps
> x86_decode_insn:3092 -> No Destination Operand
> x86_emulate_instruction:4458 -> Returned from x86_decode_insn with r = 0
>
> x86_emulate_insn:3194 -> starting special_insn...
> x86_emulate_insn:3196 -> c->eip = 3226138256
> x86_emulate_insn:3565 -> starting writeback...
> writeback:1178 -> c->eip = 2147483648
> x86_emulate_instruction:4538 -> Return from x86_emulate_insn with code
> r = 0
> ---------------------------8<-----------------------------------------------
>
>
> So the next instruction will be emulated reading the opcode with
> eip=2147483648 as stated before
> but the emulation fails with the following debug trace
>
> ---------------------------8<-----------------------------------------------
>
> x86_decode_insn:2705 -> Starting New Instruction Decode
>
> x86_decode_insn:2709 -> c->eip = ctxt->eip = 2147483648
> x86_decode_insn:2757 -> Read opcode from eip
> kvm_read_guest_virt_helper:3724 -> gpa == UNMAPPED_GVA return
> X86EMUL_PROPAGATE_FAULT
> do_fetch_insn_byte:573 -> ops->fetch returns an error
> ---------------------------8<------------------------------------------------
>
The instruction has returned to an EIP that is outside RAM, so kvm is
unable to fetch the next instruction. This is likely due to a bug (in
kvm or the guest) that has occurred much earlier.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2011-05-09 8:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-05 15:05 X86EMUL_PROPAGATE_FAULT Matteo
2011-05-09 8:50 ` Avi Kivity [this message]
2011-05-15 22:31 ` X86EMUL_PROPAGATE_FAULT kvm
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