Re: [Xen-devel] [PATCH for-4.7] x86/hvm: Correct emulation of invlpg instruction

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 22/04/16 10:57, Jan Beulich wrote:
>>>> On 22.04.16 at 11:48, <Paul.Durrant@xxxxxxxxxx> wrote:
>>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>>> Sent: 22 April 2016 10:31
>>>>>> On 22.04.16 at 10:59, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> --- a/xen/arch/x86/hvm/emulate.c
>>>> +++ b/xen/arch/x86/hvm/emulate.c
>>>> @@ -1598,8 +1598,27 @@ static int hvmemul_invlpg(
>>>>      rc = hvmemul_virtual_to_linear(
>>>>          seg, offset, 1, &reps, hvm_access_none, hvmemul_ctxt, &addr);
>>>>
>>>> -    if ( rc == X86EMUL_OKAY )
>>>> +    switch ( rc )
>>>> +    {
>>>> +    case X86EMUL_OKAY:
>>>>          hvm_funcs.invlpg_intercept(addr);
>>>> +        break;
>>>> +
>>>> +    case X86EMUL_EXCEPTION:
>>>> +        ASSERT(hvmemul_ctxt->trap.vector == TRAP_gp_fault);
>>>> +        /*
>>>> +         * `invlpg` and `invlpga` are specified to be NOPs when issued on 
>>>> a
>>>> +         * non-canonical address.  hvmemul_virtual_to_linear() latches a 
>>>> #GP
>>>> +         * which is the useful behaviour for most of its callers.
>>> Here and in the description I'd prefer you to not exclusively refer
>>> to non-canonical addresses - segment limit violations in 32-bit or
>>> compatibility modes are affected as much.
>> ...in which case squashing the #GP would be incorrect, right?
> No, not according to the SDM.

I should check and only squash a #GP(0)

#GP(sel) or #SS(sel) should not be squashed.

v2 on its way.

~Andrew

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