From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Mark Rutland <mark.rutland@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Marc Zyngier <marc.zyngier@arm.com>,
Christoffer Dall <christoffer.dall@arm.com>,
James Morse <james.morse@arm.com>,
kvmarm@lists.cs.columbia.edu,
Julien Thierry <julien.thierry.kdev@gmail.com>
Subject: [PATCH] arm64/kvm: remove VMID rollover I-cache maintenance
Date: Tue, 6 Aug 2019 16:57:37 +0100 [thread overview]
Message-ID: <20190806155737.39307-1-mark.rutland@arm.com> (raw)
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>
Cc: James Morse <james.morse@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
---
arch/arm64/kvm/hyp/tlb.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/hyp/tlb.c b/arch/arm64/kvm/hyp/tlb.c
index d49a14497715..c466060b76d6 100644
--- a/arch/arm64/kvm/hyp/tlb.c
+++ b/arch/arm64/kvm/hyp/tlb.c
@@ -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);
}
--
2.11.0
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next reply other threads:[~2019-08-06 15:57 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-06 15:57 Mark Rutland [this message]
2019-08-16 13:39 ` [PATCH] arm64/kvm: remove VMID rollover I-cache maintenance James Morse
2019-08-18 17:42 ` Marc Zyngier
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