Re: [PULL 10/30] ppc/spapr: H_ENTER_NESTED should restore host XER ca field

["Nicholas Piggin" <npiggin@gmail.com>]

On Tue Jun 27, 2023 at 7:45 AM AEST, Cédric Le Goater wrote:
> On 6/26/23 14:26, Michael Tokarev wrote:
> > 26.06.2023 08:56, Cédric Le Goater wrote:
> >> From: Nicholas Piggin <npiggin@gmail.com>
> >>
> >> Fix missing env->ca restore when going from L2 back to the host.
> >>
> >> Fixes: 120f738a467 ("spapr: implement nested-hv capability for the virtual hypervisor")
> >> Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> >> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> >> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> >> ---
> >>   hw/ppc/spapr_hcall.c | 1 +
> >>   1 file changed, 1 insertion(+)
> >>
> >> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> >> index b9047555757f..0582b524d108 100644
> >> --- a/hw/ppc/spapr_hcall.c
> >> +++ b/hw/ppc/spapr_hcall.c
> >> @@ -1773,6 +1773,7 @@ out_restore_l1:
> >>       env->cfar = spapr_cpu->nested_host_state->cfar;
> >>       env->xer = spapr_cpu->nested_host_state->xer;
> >>       env->so = spapr_cpu->nested_host_state->so;
> >> +    env->ca = spapr_cpu->nested_host_state->ca;
> >>       env->ov = spapr_cpu->nested_host_state->ov;
> >>       env->ov32 = spapr_cpu->nested_host_state->ov32;
> >>       env->ca32 = spapr_cpu->nested_host_state->ca32;
> > 
> > Is it -stable material too, or don't bother?
> > 120f738a467 is 7.0.
>
> I would say so. The CPU is missing state (Carry bit) when restoring context,
> it could be important for some instructions.
>
> Nick, did you have specific test case ?

No I just found it when doing the conversion to the new host save
structure. Now I think about it again, XER is volatile across hcalls
in general so I think the patch is not fixing any practical bug.

Thanks,
Nick