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

[Will Deacon <will@kernel.org>]

On Wed, Oct 21, 2020 at 11:05:10AM +0100, Marc Zyngier wrote:
> On 2020-10-20 15:40, Rob Herring wrote:
> > On Thu, Sep 24, 2020 at 8:48 AM Rob Herring <robh@kernel.org> 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: Marc Zyngier <maz@kernel.org>
> > > Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> > > Cc: kvmarm@lists.cs.columbia.edu
> > > Signed-off-by: Rob Herring <robh@kernel.org>
> > > ---
> > > v6:
> > > - Do dmb on kernel_exit rather than disabling interrupts around PAR
> > > read
> > > v5:
> > > - Rebase on v5.9-rc3
> > > - Disable interrupts around PAR reads
> > > - Add DMB on return to guest
> > > 
> > > v4:
> > > - Move read_sysreg_par out of KVM code to sysreg.h to share
> > > - Also use read_sysreg_par in fault.c and kvm/sys_regs.c
> > > - Use alternative f/w for dmbs around PAR read
> > > - Use cpus_have_final_cap instead of cpus_have_const_cap
> > > - Add note about speculation of PAR read
> > > 
> > > v3:
> > > - Add dmbs around PAR reads in KVM code
> > > - Clean-up 'work-around' and 'errata'
> > > 
> > > v2:
> > > - Don't disable KVM, just print warning
> > > ---
> > >  Documentation/arm64/silicon-errata.rst     |  2 ++
> > >  arch/arm64/Kconfig                         | 20 ++++++++++++++++++++
> > >  arch/arm64/include/asm/cpucaps.h           |  3 ++-
> > >  arch/arm64/include/asm/sysreg.h            |  9 +++++++++
> > >  arch/arm64/kernel/cpu_errata.c             | 10 ++++++++++
> > >  arch/arm64/kernel/entry.S                  |  3 +++
> > >  arch/arm64/kvm/arm.c                       |  3 ++-
> > >  arch/arm64/kvm/hyp/include/hyp/switch.h    | 21 +++++++++++++--------
> > >  arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h |  2 +-
> > >  arch/arm64/kvm/hyp/nvhe/switch.c           |  2 +-
> > >  arch/arm64/kvm/hyp/vhe/switch.c            |  2 +-
> > >  arch/arm64/kvm/sys_regs.c                  |  2 +-
> > >  arch/arm64/mm/fault.c                      |  2 +-
> > >  13 files changed, 66 insertions(+), 15 deletions(-)
> > 
> > Marc, Can I get an ack for KVM on this? Will is waiting for one before
> > applying.
> 
> Here you go:
> 
> Acked-by: Marc Zyngier <maz@kernel.org>

Cheers, Marc.

Rob -- can you repost this based on -rc1 please?

Will

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