Re: [PATCH v7 2/2] arm64: Add workaround for Arm Cortex-A77 erratum 1508412

[Rob Herring <robh@kernel.org>]

On Thu, Oct 29, 2020 at 5:04 AM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Wed, Oct 28, 2020 at 01:28:39PM -0500, Rob Herring wrote:
> > On Cortex-A77 r0p0 and r1p0, a sequence of a non-cacheable or device load
> > and a store exclusive or PAR_EL1 read can cause a deadlock.
> >
> > The workaround requires a DMB SY before and after a PAR_EL1 register
> > read. In addition, it's possible an interrupt (doing a device read) or
> > KVM guest exit could be taken between the DMB and PAR read, so we
> > also need a DMB before returning from interrupt and before returning to
> > a guest.
> >
> > A deadlock is still possible with the workaround as KVM guests must also
> > have the workaround. IOW, a malicious guest can deadlock an affected
> > systems.
> >
> > This workaround also depends on a firmware counterpart to enable the h/w
> > to insert DMB SY after load and store exclusive instructions. See the
> > errata document SDEN-1152370 v10 [1] for more information.
> >
> > [1] https://static.docs.arm.com/101992/0010/Arm_Cortex_A77_MP074_Software_Developer_Errata_Notice_v10.pdf
> >
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: James Morse <james.morse@arm.com>
> > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> > Cc: kvmarm@lists.cs.columbia.edu
> > Acked-by: Marc Zyngier <maz@kernel.org>
> > Signed-off-by: Rob Herring <robh@kernel.org>
>
> I thought I reviewed the v6 already and that's just a rebase. Here it is
> again:
>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

You did. Sorry, I forgot to add it.

Rob
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