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

Marc Zyngier
2020-10-21T10:06:47Z

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>

M.
--
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