Re: [PATCH] KVM: x86: emulate: correct page fault error code for NoWrite instructions

[Wanpeng Li]

2015-11-20 10:52 GMT+08:00 Wanpeng Li :
> Hi Paolo,
> 2015-02-09 17:03 GMT+08:00 Paolo Bonzini :
>> NoWrite instructions (e.g. cmp or test) never set the "write access"
>> bit in the error code, even if one of the operands is treated as a
>> destination.
>
> Sorry to reply to an old commit, btw, could you point out where in SDM
> describe above?

I see.
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Re: [PATCH] KVM: x86: emulate: correct page fault error code for NoWrite instructions

[Wanpeng Li]

Hi Paolo,
2015-02-09 17:03 GMT+08:00 Paolo Bonzini :
> NoWrite instructions (e.g. cmp or test) never set the "write access"
> bit in the error code, even if one of the operands is treated as a
> destination.

Sorry to reply to an old commit, btw, could you point out where in SDM
describe above?

Regards,
Wanpeng Li
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Re: [PATCH] KVM: x86: emulate: correct page fault error code for NoWrite instructions

[Nadav Amit]

Wanpeng Li  wrote:

> 2015-11-20 10:52 GMT+08:00 Wanpeng Li :
>> Hi Paolo,
>> 2015-02-09 17:03 GMT+08:00 Paolo Bonzini :
>>> NoWrite instructions (e.g. cmp or test) never set the "write access"
>>> bit in the error code, even if one of the operands is treated as a
>>> destination.
>> 
>> Sorry to reply to an old commit, btw, could you point out where in SDM
>> describe above?
> 
> I see.

I don’t understand whether you still need my help, so to clarify: on a
page-fault the error code should indicate whether the access was due to a
write access. Previously KVM marked it as “write access” for instructions
such as test and cmp that do not perform write.

Nadav--
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Re: [PATCH] KVM: x86: emulate: correct page fault error code for NoWrite instructions

[Nadav Amit]

Sorry for that. I’ll try to run some few more tests next week.

Nadav

Paolo Bonzini pbonz...@redhat.com wrote:

 NoWrite instructions (e.g. cmp or test) never set the write access
 bit in the error code, even if one of the operands is treated as a
 destination.
 
 Fixes: c205fb7d7d4f81e46fc577b707ceb9e356af1456
 Cc: Nadav Amit na...@cs.technion.ac.il
 Signed-off-by: Paolo Bonzini pbonz...@redhat.com
 ---
 arch/x86/kvm/emulate.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
 
 diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
 index 81dcf7964701..a943bf0c06d0 100644
 --- a/arch/x86/kvm/emulate.c
 +++ b/arch/x86/kvm/emulate.c
 @@ -4954,7 +4954,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
   rc = segmented_read(ctxt, ctxt-dst.addr.mem,
  ctxt-dst.val, ctxt-dst.bytes);
   if (rc != X86EMUL_CONTINUE) {
 - if (rc == X86EMUL_PROPAGATE_FAULT 
 + if (!(ctxt-d  NoWrite) 
 + rc == X86EMUL_PROPAGATE_FAULT 
   ctxt-exception.vector == PF_VECTOR)
   ctxt-exception.error_code |= PFERR_WRITE_MASK;
   goto done;
 -- 
 1.8.3.1
 
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