On Fri, 16 Aug 2019 14:39:31 +0100
James Morse <james.morse@xxxxxxx> wrote:
> Hi Mark,
>
> On 06/08/2019 16:57, Mark Rutland wrote:
> > For VPIPT I-caches, we need I-cache maintenance on VMID rollover to
> > avoid an ABA problem. Consider a single vCPU VM, with a pinned stage-2,
> > running with an idmap VA->IPA and idmap IPA->PA. If we don't do
> > maintenance on rollover:
> >
> > // VMID A
> > Writes insn X to PA 0xF
> > Invalidates PA 0xF (for VMID A)
> >
> > I$ contains [{A,F}->X]
> >
> > [VMID ROLLOVER]
> >
> > // VMID B
> > Writes insn Y to PA 0xF
> > Invalidates PA 0xF (for VMID B)
> >
> > I$ contains [{A,F}->X, {B,F}->Y]
> >
> > [VMID ROLLOVER]
> >
> > // VMID A
> > I$ contains [{A,F}->X, {B,F}->Y]
> >
> > Unexpectedly hits stale I$ line {A,F}->X.
> >
> > However, for PIPT and VIPT I-caches, the VMID doesn't affect lookup or
> > constrain maintenance. Given the VMID doesn't affect PIPT and VIPT
> > I-caches, and given VMID rollover is independent of changes to stage-2
> > mappings, I-cache maintenance cannot be necessary on VMID rollover for
> > PIPT or VIPT I-caches.
> >
> > This patch removes the maintenance on rollover for VIPT and PIPT
> > I-caches. At the same time, the unnecessary colons are removed from the
> > asm statement to make it more legible.
>
> Makes sense!
>
> Reviewed-by: James Morse <james.morse@xxxxxxx>
Queued for 5.4. Thanks both.
M.
--
Without deviation from the norm, progress is not possible.
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