From: Stephen Boyd <swboyd@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Andre Przywara <andre.przywara@arm.com>,
Steven Price <steven.price@arm.com>,
Marc Zyngier <maz@kernel.org>,
stable@vger.kernel.org
Subject: Re: [PATCH 1/2] arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED
Date: Wed, 21 Oct 2020 15:06:35 -0700 [thread overview]
Message-ID: <160331799505.884498.376133101315233761@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <20201021211326.GA18548@willie-the-truck>
Quoting Will Deacon (2020-10-21 14:13:26)
> On Wed, Oct 21, 2020 at 09:12:02AM -0700, Stephen Boyd wrote:
>
> > My read of the spec was that the intent is to remove the call at some
> > point and have the removal of the call mean that it isn't vulnerable.
>
> No, the CSV2 field in whichever ID register is for that. We check that in
> spectre_v2_get_cpu_hw_mitigation_state().
Alright, makes sense!
>
> > Because NOT_SUPPORTED per the spec means "not needed", "maybe needed",
> > or "firmware doesn't know". Aha maybe they wanted us to make the call on
> > each CPU (i.e. PE) and then if any of them return 0 we should consider
> > it vulnerable and if they return NOT_SUPPORTED we should keep calling
> > for each CPU until we are sure we don't see a 0 and only see a 1 or
> > NOT_SUPPORTED? Looks like a saturating value sort of thing, across CPUs
> > that we care/know about.
>
> The mitigation state is always per-cpu because of big/little systems, there
> just isn't a short-cut for the firmware to say "all CPUs are unaffected"
> like there is for SMCCC_ARCH_WORKAROUND_2 with its "NOT_REQUIRED" return
> code.
>
Ok. Can/should kvm be emulating the CSV2 bit that the guest sees? Just
wondering why I'm falling into this (ghost) trap in the first place.
next prev parent reply other threads:[~2020-10-21 22:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 21:45 [PATCH 0/2] arm64: Fixes for spectre-v2 detection in guest kernels Stephen Boyd
2020-10-20 21:45 ` [PATCH 1/2] arm64: ARM_SMCCC_ARCH_WORKAROUND_1 doesn't return SMCCC_RET_NOT_REQUIRED Stephen Boyd
2020-10-21 7:57 ` Will Deacon
2020-10-21 10:23 ` Marc Zyngier
2020-10-21 12:43 ` Will Deacon
2020-10-21 15:23 ` Stephen Boyd
2020-10-21 15:49 ` Will Deacon
2020-10-21 16:12 ` Stephen Boyd
2020-10-21 21:13 ` Will Deacon
2020-10-21 22:06 ` Stephen Boyd [this message]
2020-10-20 21:45 ` [PATCH 2/2] arm64: proton-pack: Update comment to reflect new function name Stephen Boyd
2020-10-21 15:44 ` [PATCH 0/2] arm64: Fixes for spectre-v2 detection in guest kernels Will Deacon
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