Subject: Re: [PATCH v6 2/2] arm64: Add workaround for Arm Cortex-A77 erratum 1508412

From: Catalin Marinas <[email-masked]>
Date: Thu, 24 Sep 2020 17:52:51 +0100

On Thu, Sep 24, 2020 at 07:48:53AM -0600, 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 <[email-masked]>
> Cc: James Morse <[email-masked]>
> Cc: Suzuki K Poulose <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> Cc: Marc Zyngier <[email-masked]>
> Cc: Julien Thierry <[email-masked]>
> Cc: [email-masked]
> Signed-off-by: Rob Herring <[email-masked]>

Reviewed-by: Catalin Marinas <[email-masked]>

I'll leave these patches to Will for 5.10.

Thanks.

-- 
Catalin

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