Re: [Qemu-devel] [PATCH± SVM I/O permission bitmap for user-level (ring-3) code ignored

[Paolo Bonzini]

On 05/03/2017 19:21, Alexander Boettcher wrote:
> the SVM I/O permission bitmap for user-level (ring-3) VM code running in
> SVM seems to be ignored and causes a GP-fault. (Actual the IO permission
> was granted by the kernel via the TSS I/O port permission bitmap).
> 
> After some debugging the GP code originates from target/i386/translate.c
> gen_check_io() within the if(s->pe && (s->cpl > s->iopl || s->vm86))
> condition. However, the actual SVM IO permission bitmap is checked after
> that condition, which succeeds and would permit the access.

>From your message it's not clear what is going wrong.  The code as is
written now matches the AMD manual: "Exceptions related to virtual x86
mode, IOPL, or the TSS-bitmap are checked before the SVM intercept
check. All other exceptions are checked after the SVM intercept check".

Please explain better what is going on:

1) does the TSS I/O permission bitmap grant permission to access the
port (the answer seems to be yes here)?

2) does the SVM I/O permission bitmap grant permission to access the port?

3) you get a #GP, do you expect the access to be trapped to the
hypervisor or not?

4) what is the exact instruction that the user-level code is executing?

Paolo