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arm64/kvm: Remove VMID rollover I-cache maintenance

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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.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Mark Rutland 2019-08-06 16:57:37 +01:00 committed by Marc Zyngier
parent 41108170d9
commit 363de99b77
1 changed files with 13 additions and 1 deletions
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14
arch/arm64/kvm/hyp/tlb.c
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@ -193,6 +193,18 @@ void __hyp_text __kvm_flush_vm_context(void)
{
dsb(ishst);
__tlbi(alle1is);
asm volatile("ic ialluis" : : );
/*
* VIPT and PIPT caches are not affected by VMID, so no maintenance
* is necessary across a VMID rollover.
*
* VPIPT caches constrain lookup and maintenance to the active VMID,
* so we need to invalidate lines with a stale VMID to avoid an ABA
* race after multiple rollovers.
*
*/
if (icache_is_vpipt())
asm volatile("ic ialluis");
dsb(ish);
}