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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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