Re: [PATCH v3 3/6] irqchip, gicv3: Workaround for Cavium ThunderX erratum 23154
From: Marc Zyngier
Date: Fri Aug 14 2015 - 10:08:27 EST
On 14/08/15 14:18, Robert Richter wrote:
> From: Robert Richter <rrichter@xxxxxxxxxx>
>
> This patch implements Cavium ThunderX erratum 23154.
>
> The gicv3 of ThunderX requires a modified version for reading the IAR
> status to ensure data synchronization. Since this is in the fast-path
> and called with each interrupt, runtime patching is used using jump
> label patching for smallest overhead (no-op). This is the same
> technique as used for tracepoints.
>
> v3:
> * fix erratum to be dependend from midr
> * use arm64 errata framework
>
> v2:
> * implement code in a single asm() to keep instruction sequence
> * added comment to the code that explains the erratum
> * apply workaround also if running as guest, thus check MIDR
>
> Signed-off-by: Robert Richter <rrichter@xxxxxxxxxx>
> ---
> arch/arm64/Kconfig | 11 +++++++++
> arch/arm64/include/asm/cpufeature.h | 3 ++-
> arch/arm64/include/asm/cputype.h | 18 ++++++++------
> arch/arm64/kernel/cpu_errata.c | 9 +++++++
> drivers/irqchip/irq-gic-v3.c | 49 ++++++++++++++++++++++++++++++++++++-
> 5 files changed, 81 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 0f6edb14b7e4..4f866a4c6536 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -417,6 +417,17 @@ config ARM64_ERRATUM_845719
>
> If unsure, say Y.
>
> +config CAVIUM_ERRATUM_23154
> + bool "Cavium erratum 23154: Access to ICC_IAR1_EL1 is not sync'ed"
> + depends on ARCH_THUNDER
> + default y
> + help
> + The gicv3 of ThunderX requires a modified version for
> + reading the IAR status to ensure data synchronization
> + (access to icc_iar1_el1 is not sync'ed before and after).
> +
> + If unsure, say Y.
> +
> endmenu
>
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index c1044218a63a..2a5e4c163ee5 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -25,8 +25,9 @@
> #define ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE 1
> #define ARM64_WORKAROUND_845719 2
> #define ARM64_HAS_SYSREG_GIC_CPUIF 3
> +#define ARM64_WORKAROUND_CAVIUM_23154 4
>
> -#define ARM64_NCAPS 4
> +#define ARM64_NCAPS 5
>
> #ifndef __ASSEMBLY__
>
> diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
> index a84ec605bed8..3f0c7683f252 100644
> --- a/arch/arm64/include/asm/cputype.h
> +++ b/arch/arm64/include/asm/cputype.h
> @@ -62,15 +62,19 @@
> (0xf << MIDR_ARCHITECTURE_SHIFT) | \
> ((partnum) << MIDR_PARTNUM_SHIFT))
>
> -#define ARM_CPU_IMP_ARM 0x41
> -#define ARM_CPU_IMP_APM 0x50
> +#define ARM_CPU_IMP_ARM 0x41
> +#define ARM_CPU_IMP_APM 0x50
> +#define ARM_CPU_IMP_CAVIUM 0x43
>
> -#define ARM_CPU_PART_AEM_V8 0xD0F
> -#define ARM_CPU_PART_FOUNDATION 0xD00
> -#define ARM_CPU_PART_CORTEX_A57 0xD07
> -#define ARM_CPU_PART_CORTEX_A53 0xD03
> +#define ARM_CPU_PART_AEM_V8 0xD0F
> +#define ARM_CPU_PART_FOUNDATION 0xD00
> +#define ARM_CPU_PART_CORTEX_A57 0xD07
> +#define ARM_CPU_PART_CORTEX_A53 0xD03
> +
> +#define APM_CPU_PART_POTENZA 0x000
> +
> +#define CAVIUM_CPU_PART_THUNDERX 0x0A1
>
> -#define APM_CPU_PART_POTENZA 0x000
>
> #define ID_AA64MMFR0_BIGENDEL0_SHIFT 16
> #define ID_AA64MMFR0_BIGENDEL0_MASK (0xf << ID_AA64MMFR0_BIGENDEL0_SHIFT)
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 6ffd91438560..574450c257a4 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -23,6 +23,7 @@
>
> #define MIDR_CORTEX_A53 MIDR_CPU_PART(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A53)
> #define MIDR_CORTEX_A57 MIDR_CPU_PART(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A57)
> +#define MIDR_THUNDERX MIDR_CPU_PART(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX)
>
> #define CPU_MODEL_MASK (MIDR_IMPLEMENTOR_MASK | MIDR_PARTNUM_MASK | \
> MIDR_ARCHITECTURE_MASK)
> @@ -82,6 +83,14 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
> MIDR_RANGE(MIDR_CORTEX_A53, 0x00, 0x04),
> },
> #endif
> +#ifdef CONFIG_CAVIUM_ERRATUM_23154
> + {
> + /* Cavium ThunderX, pass 1.x */
> + .desc = "Cavium erratum 23154",
> + .capability = ARM64_WORKAROUND_CAVIUM_23154,
> + MIDR_RANGE(MIDR_THUNDERX, 0x00, 0x01),
> + },
> +#endif
> {
> }
> };
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 1a91902be0b1..59a5f13f3c10 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -107,7 +107,7 @@ static void gic_redist_wait_for_rwp(void)
> }
>
> /* Low level accessors */
> -static u64 __maybe_unused gic_read_iar(void)
> +static u64 gic_read_iar_common(void)
> {
> u64 irqstat;
>
> @@ -115,6 +115,38 @@ static u64 __maybe_unused gic_read_iar(void)
> return irqstat;
> }
>
> +/*
> + * Cavium ThunderX erratum 23154
> + *
> + * The gicv3 of ThunderX requires a modified version for reading the
> + * IAR status to ensure data synchronization (access to icc_iar1_el1
> + * is not sync'ed before and after).
> + */
> +static u64 gic_read_iar_cavium_thunderx(void)
> +{
> + u64 irqstat;
> +
> + asm volatile(
> + "nop;nop;nop;nop\n\t"
> + "nop;nop;nop;nop\n\t"
> + "mrs_s %0, " __stringify(ICC_IAR1_EL1) "\n\t"
> + "nop;nop;nop;nop"
> + : "=r" (irqstat));
> + mb();
> +
> + return irqstat;
> +}
> +
> +struct static_key is_cavium_thunderx = STATIC_KEY_INIT_FALSE;
> +
> +static u64 __maybe_unused gic_read_iar(void)
> +{
> + if (static_key_false(&is_cavium_thunderx))
> + return gic_read_iar_common();
> + else
> + return gic_read_iar_cavium_thunderx();
> +}
> +
> static void __maybe_unused gic_write_pmr(u64 val)
> {
> asm volatile("msr_s " __stringify(ICC_PMR_EL1) ", %0" : : "r" (val));
> @@ -766,8 +798,23 @@ static const struct irq_domain_ops gic_irq_domain_ops = {
> .free = gic_irq_domain_free,
> };
>
> +static void gicv3_enable_cavium_thunderx(void *data)
> +{
> + static_key_slow_inc(&is_cavium_thunderx);
> +}
> +
> static const struct gic_capabilities gicv3_errata[] = {
> {
> + /*
> + * Need to be applied in guests too, thus use cpu
> + * detection as iidr is emulated with different vendor
> + * id.
> + */
> + .desc = "GIC: Cavium erratum 23154",
> + .cpu_cap = ARM64_WORKAROUND_CAVIUM_23154,
> + .init = gicv3_enable_cavium_thunderx,
> + },
> + {
> }
> };
>
>
Robert,
I probably didn't express myself very well, because this not what I had
in mind, sorry...
I think this is very much overdesigned for something that should be very
simple. Why can't you have a simple:
if (cpu_have_feature(ARM64_WORKAROUND_CAVIUM_23154))
static_key_slow_inc(&is_cavium_thunderx);
No need for a cpu_cap field, no need to special-case feature 0, and it
keeps the code fairly readable. You can even hide it in a
gic_enable_cpu_quirks() function.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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