Re: [PATCH v2 3/3] arm64: Add workaround for Arm Cortex-A77 erratum 1508412

[Will Deacon <will@kernel.org>]

On Wed, Jul 01, 2020 at 03:53:08PM -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
> and the disabling of KVM. KVM must be disabled to prevent the problematic
> sequence in guests' EL1. 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.

This ^^ is out of date not that we're not disabling KVM.

> All the other PAR_EL1 reads besides the one in
> is_spurious_el1_translation_fault() are in KVM code, so the work-around is
> not needed for them.

And I think this now needs some extra work.

> [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>
> ---
> v2:
> - Don't disable KVM, just print warning
> ---
>  Documentation/arm64/silicon-errata.rst |  2 ++
>  arch/arm64/Kconfig                     | 19 +++++++++++++++++++
>  arch/arm64/include/asm/cpucaps.h       |  3 ++-
>  arch/arm64/kernel/cpu_errata.c         | 10 ++++++++++
>  arch/arm64/kvm/arm.c                   |  3 ++-
>  arch/arm64/mm/fault.c                  | 10 ++++++++++
>  6 files changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index 936cf2a59ca4..716b279e3b33 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -90,6 +90,8 @@ stable kernels.
>  +----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Cortex-A76      | #1463225        | ARM64_ERRATUM_1463225       |
>  +----------------+-----------------+-----------------+-----------------------------+
> +| ARM            | Cortex-A77      | #1508412        | ARM64_ERRATUM_1508412       |
> ++----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Neoverse-N1     | #1188873,1418040| ARM64_ERRATUM_1418040       |
>  +----------------+-----------------+-----------------+-----------------------------+
>  | ARM            | Neoverse-N1     | #1349291        | N/A                         |
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index a4a094bedcb2..28993ad4c649 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -626,6 +626,25 @@ config ARM64_ERRATUM_1542419
>  
>  	  If unsure, say Y.
>  
> +config ARM64_ERRATUM_1508412
> +	bool "Cortex-A77: 1508412: workaround deadlock on sequence of NC/Device load and store exclusive or PAR read"
> +	default y
> +	help
> +	  This option adds a workaround for Arm Cortex-A77 erratum 1508412.
> +
> +	  Affected Cortex-A77 cores (r0p0, r1p0) could deadlock on a sequence
> +	  of a store-exclusive or read of PAR_EL1 and a load with device or
> +	  non-cacheable memory attributes. The workaround depends on a firmware
> +	  counterpart.
> +
> +	  KVM guests must also have the work-around implemented or they can

work-around => workaround

> +	  deadlock the system.
> +
> +	  Workaround the issue by inserting DMB SY barriers around PAR_EL1

Workaround => work around

> +	  register reads and warning KVM users.
> +
> +	  If unsure, say Y.
> +
>  config CAVIUM_ERRATUM_22375
>  	bool "Cavium erratum 22375, 24313"
>  	default y
> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> index d7b3bb0cb180..2a2cdb4ced8b 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -62,7 +62,8 @@
>  #define ARM64_HAS_GENERIC_AUTH			52
>  #define ARM64_HAS_32BIT_EL1			53
>  #define ARM64_BTI				54
> +#define ARM64_WORKAROUND_1508412		55
>  
> -#define ARM64_NCAPS				55
> +#define ARM64_NCAPS				56
>  
>  #endif /* __ASM_CPUCAPS_H */
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index ad06d6802d2e..5eee8a75540c 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -938,6 +938,16 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>  		.matches = has_neoverse_n1_erratum_1542419,
>  		.cpu_enable = cpu_enable_trap_ctr_access,
>  	},
> +#endif
> +#ifdef CONFIG_ARM64_ERRATUM_1508412
> +	{
> +		/* we depend on the firmware portion for correctness */
> +		.desc = "ARM erratum 1508412 (kernel portion)",
> +		.capability = ARM64_WORKAROUND_1508412,
> +		ERRATA_MIDR_RANGE(MIDR_CORTEX_A77,
> +				  0, 0,
> +				  1, 0),
> +	},
>  #endif
>  	{
>  	}
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index e2f50fa4d825..9f50e01eea00 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1653,7 +1653,8 @@ int kvm_arch_init(void *opaque)
>  		return -ENODEV;
>  	}
>  
> -	if (cpus_have_const_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE))
> +	if (cpus_have_const_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
> +	    cpus_have_const_cap(ARM64_WORKAROUND_1508412))
>  		kvm_info("Guests without required CPU erratum work-arounds can deadlock system!\n" \
>  			 "Only trusted guests should be used on this system.\n");
>  
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 8afb238ff335..d599d60f06fd 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -260,7 +260,17 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
>  	local_irq_save(flags);
>  	asm volatile("at s1e1r, %0" :: "r" (addr));
>  	isb();
> +	/*
> +	 * Arm Errata 1508412 requires dmb(sy) before and after reads of

Errata => erratum

Will
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