From: Will Deacon <will@kernel.org>
To: Andrew Scull <ascull@google.com>
Cc: "qwandor@google.com" <qwandor@google.com>,
"qperret@google.com" <qperret@google.com>,
Marc Zyngier <maz@kernel.org>,
Suzuki Poulose <Suzuki.Poulose@arm.com>,
Steven Price <steven.price@arm.com>,
"wedsonaf@google.com" <wedsonaf@google.com>,
"tabba@google.com" <tabba@google.com>,
James Morse <James.Morse@arm.com>,
"dbrazdil@google.com" <dbrazdil@google.com>,
"kernel-team@android.com" <kernel-team@android.com>,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH] arm64: unify WORKAROUND_SPECULATIVE_AT_{NVHE,VHE}
Date: Fri, 17 Apr 2020 17:41:04 +0100 [thread overview]
Message-ID: <20200417164103.GA12362@willie-the-truck> (raw)
In-Reply-To: <20200403125726.GA33049@google.com>
On Fri, Apr 03, 2020 at 01:57:26PM +0100, Andrew Scull wrote:
> On Fri, Mar 27, 2020 at 02:59:47PM +0000, Steven Price wrote:
> > I proposed something similar a while ago[1], but Marc was concerned about
> > the microarch detail[2] and hence I split the workaround into VHE/non-VHE.
> >
> > That said I'm not saying this is necessarily wrong, just that we'd need some
> > more information on whether the non-VHE workaround is suitable for the CPUs
> > we're currently forcing VHE on.
>
> We noticed that both the nVHE and VHE workarounds share the same
> assumption that the EPDx bits are not being cached in the TLB.
>
> `__tlb_switch_to_guest_vhe` and `__tlb_switch_to_guest_nvhe` are both
> setting EPDx as part of the workaround. However, neither handles the
> possibility of a speculative AT being able to make use of a cached EPD=0
> value in the TLB in order to allocate bad TLB entries.
>
> If this is correct, the microarch concern appears to have been solved
> already. Otherwise, or if we are unsure, we should go ahead and add the
> TLB flushes to keep this safe.
I think Andrew's right here. Can we go ahead with the original approach of
combining the workarounds, or is there something we've missed?
Cheers,
Will
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next prev parent reply other threads:[~2020-04-17 16:41 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-27 14:39 [RFC PATCH] arm64: unify WORKAROUND_SPECULATIVE_AT_{NVHE,VHE} Andrew Scull
2020-03-27 14:59 ` Steven Price
2020-03-27 17:48 ` Andrew Scull
2020-03-27 17:52 ` Marc Zyngier
2020-03-27 18:09 ` Will Deacon
2020-03-28 11:23 ` Marc Zyngier
2020-03-30 10:06 ` Will Deacon
2020-04-03 12:57 ` Andrew Scull
2020-04-17 16:41 ` Will Deacon [this message]
2020-04-20 13:46 ` Steven Price
2020-03-27 16:11 ` James Morse
2020-03-27 16:59 ` Will Deacon
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