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

[Catalin Marinas]

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 at arm.com>
> Cc: James Morse <james.morse at arm.com>
> Cc: Suzuki K Poulose <suzuki.poulose at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Julien Thierry <julien.thierry.kdev at gmail.com>
> Cc: kvmarm at lists.cs.columbia.edu
> Acked-by: Marc Zyngier <maz at kernel.org>
> Signed-off-by: Rob Herring <robh at 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 at arm.com>