Re: [DROP][PATCH] KVM: x86: Fix the #GP(0) and #UD conditions for XSETBV emulation

[Paolo Bonzini]

On 1/20/22 10:31, Xiaoyao Li wrote:
> > So while my gut feeling that #UD would not cause a vmexit was correct,
> > technically I was reading the SDM incorrectly.
>
> SDM also states
>
>    Certain exceptions have priority over VM exits. These include
>    invalid-opcode exception, faults based on privilege level,
>    and general-protection exceptions that are based on checking
>    I/O permission bits in the task-state segment(TSS)
>
> in "Relative Priority of Faults and VM Exits"
>
> So my understanding is that the architectural check always takes the 
> higher priority than VM exit.

Good point!  It's right above in 25.1.1.  I was confused by the specific 
mention of GETSEC, but the reason for the footnote is because undefined 
GETSEC leaves cause a vmexit instead of #UD, and GETSEC vmexits also 
override #GP faults based on privilege level.

Thanks,

Paolo