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>
Thanks,
James
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