Re: [PATCH v4 4/4] arm64: Work around Falkor erratum 1009

Will Deacon
2017-01-27T15:07:29Z

On Wed, Jan 25, 2017 at 10:52:32AM -0500, Christopher Covington wrote:
> During a TLB invalidate sequence targeting the inner shareable domain,
> Falkor may prematurely complete the DSB before all loads and stores using
> the old translation are observed. Instruction fetches are not subject to
> the conditions of this erratum. If the original code sequence includes
> multiple TLB invalidate instructions followed by a single DSB, onle one of
> the TLB instructions needs to be repeated to work around this erratum.
> While the erratum only applies to cases in which the TLBI specifies the
> inner-shareable domain (*IS form of TLBI) and the DSB is ISH form or
> stronger (OSH, SYS), this changes applies the workaround overabundantly--
> to local TLBI, DSB NSH sequences as well--for simplicity.
>
> Based on work by Shanker Donthineni <shankerd@codeaurora.org>
>
> Signed-off-by: Christopher Covington <cov@codeaurora.org>
> ---
> Documentation/arm64/silicon-errata.txt | 1 +
> arch/arm64/Kconfig | 10 ++++++++++
> arch/arm64/include/asm/cpucaps.h | 3 ++-
> arch/arm64/include/asm/tlbflush.h | 18 +++++++++++++++---
> arch/arm64/kernel/cpu_errata.c | 7 +++++++
> 5 files changed, 35 insertions(+), 4 deletions(-)

Thanks, this one looks good to me. It doesn't apply without the other
erratum workaround (due to conflicts), so I'll have to wait for the
discussion with Mark to each a conclusion before I can queue it.

One minor comment inline...

> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index deab52374119..fc434f421c7b 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -36,9 +36,21 @@
> * not. The macros handles invoking the asm with or without the
> * register argument as appropriate.
> */
> -#define __TLBI_0(op, arg) asm ("tlbi " #op)
> -#define __TLBI_1(op, arg) asm ("tlbi " #op ", %0" : : "r" (arg))
> -#define __TLBI_N(op, arg, n, ...) __TLBI_##n(op, arg)
> +#define __TLBI_0(op, arg) asm volatile ("tlbi " #op "\n" \
> + ALTERNATIVE("nop\n nop", \
> + "dsb ish\n tlbi " #op, \
> + ARM64_WORKAROUND_REPEAT_TLBI, \
> + CONFIG_QCOM_FALKOR_ERRATUM_1009) \
> + : : )
> +
> +#define __TLBI_1(op, arg) asm volatile ("tlbi " #op ", %0\n" \
> + ALTERNATIVE("nop\n nop", \
> + "dsb ish\n tlbi " #op ", %0", \
> + ARM64_WORKAROUND_REPEAT_TLBI, \
> + CONFIG_QCOM_FALKOR_ERRATUM_1009) \
> + : : "r" (arg))

I don't think you need to make these volatile.

Will