From: Marc Zyngier <maz@kernel.org>
To: Bharat Bhushan <bbhushan2@marvell.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
"will@kernel.org" <will@kernel.org>,
"daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
"konrad.dybcio@somainline.org" <konrad.dybcio@somainline.org>,
"saiprakash.ranjan@codeaurora.org"
<saiprakash.ranjan@codeaurora.org>,
"robh@kernel.org" <robh@kernel.org>,
"marcan@marcan.st" <marcan@marcan.st>,
"suzuki.poulose@arm.com" <suzuki.poulose@arm.com>,
"broonie@kernel.org" <broonie@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linu Cherian <lcherian@marvell.com>,
Sunil Kovvuri Goutham <sgoutham@marvell.com>
Subject: Re: [EXT] Re: [PATCH] clocksource: Add Marvell Errata-38627 workaround
Date: Mon, 26 Jul 2021 19:03:06 +0100 [thread overview]
Message-ID: <87fsw1dkbp.wl-maz@kernel.org> (raw)
In-Reply-To: <CO6PR18MB4465AAE7916DCFECE9D47EA2E3E89@CO6PR18MB4465.namprd18.prod.outlook.com>
Hi Bharat,
On Mon, 26 Jul 2021 05:29:53 +0100,
Bharat Bhushan <bbhushan2@marvell.com> wrote:
>
> Sorry for delayed response
>
> Please see inline
>
> > -----Original Message-----
> > From: Mark Rutland <mark.rutland@arm.com>
> > Sent: Tuesday, July 13, 2021 9:43 PM
> >
> > 1) A guest can deliberately cause information to be leaked to itself via
> > the corrupted GPRs. I haven't seen any rationale for why that is not
> > a problem, nor have I seen a suggested workaround.
> >
> > 2) A guest *may* be able to trigger this while the host is running. I
> > haven't seen anything that rules this out so far.
> >
> > 3) Even in the absence of virtualization, it would be necessary to
> > workaround this for *every* level-triggered interrupt, which includes
> > at the timer, PMU, and GIC maintenance interrupts, in addition to any
> > other configurable PPIs or SPIs.
> >
> > Without a fix that covers all of those, I don't think the
> > workaround is viable.
>
> This patch covers workaround for ARM arch timer in non-virtualized
> cases.
>
> While we are considering different scenarios which can trigger the
> issue. After discussing with HW folks internally we have come to a
> conclusion that there is no single workaround which will fix all the
> scenarios. The host timer interrupt workaround is different from
> virtualization and from other interrupt sources.
>
> While we are working on other workarounds, we want to push timer
> workaround first as currently that's the one customers are
> encountering right now and want a upstream accepted patch
> soon. Other workarounds will take time to test and qualify.
>
> Wrt drivers disabling the interrupt, except changing the driver, we
> don't see any common place where we can add a workaround. Please let
> me your take on this.
I don't think a workaround limited to the timer is viable. It is quite
obvious that once you have worked around the most likely cause for a
crash (timer interrupts), you will need to come up with yet another
workaround for another interrupt source.
We need a solution that works for all interrupts, or at the very least
all per-CPU interrupts. For global interrupts, only you can find out
how they can be mitigated. If that means changing drivers, so be it.
I understand that this isn't what you want to read, but I'm not
confident taking this patch with the knowledge that there is still a
million ways to make it fall over.
Evidently, KVM cannot be enabled on such a system. More importantly, I
cannot see how we can support users of such a machine either. How to
analyse a crash report if there is a remote possibility that the CPU
has decided to ignore a number of instructions?
To sum it up, I'm not prepared to approve such a patch until there is
a compelling story for all the interrupts that may trigger such
behaviour.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
next prev parent reply other threads:[~2021-07-26 18:03 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-05 6:08 [PATCH] clocksource: Add Marvell Errata-38627 workaround Bharat Bhushan
2021-07-05 9:07 ` Mark Rutland
2021-07-05 9:14 ` Mark Rutland
2021-07-08 10:47 ` [EXT] " Bharat Bhushan
2021-07-08 11:41 ` Mark Rutland
2021-07-13 2:40 ` Bharat Bhushan
2021-07-13 15:38 ` Marc Zyngier
2021-07-13 16:12 ` Mark Rutland
2021-07-26 4:29 ` Bharat Bhushan
2021-07-26 18:03 ` Marc Zyngier [this message]
2021-07-05 9:26 ` Marc Zyngier
2021-07-08 10:48 ` [EXT] " Bharat Bhushan
2021-07-11 9:57 ` Marc Zyngier
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