Re: [PATCH 2/3] arm64: Work around Falkor erratum 1003

Mark Rutland
2016-12-08T11:38:50Z

On Wed, Dec 07, 2016 at 03:00:26PM -0500, Christopher Covington wrote:
> From: Shanker Donthineni <shankerd@codeaurora.org>
>
> On the Qualcomm Datacenter Technologies Falkor v1 CPU, memory accesses may
> allocate TLB entries using an incorrect ASID when TTBRx_EL1 is being
> updated. Changing the TTBRx_EL1[ASID] and TTBRx_EL1[BADDR] fields
> separately using a reserved ASID will ensure that there are no TLB entries
> with incorrect ASID after changing the the ASID.
>
> Pseudo code:
> write TTBRx_EL1[ASID] to a reserved value
> ISB
> write TTBRx_EL1[BADDR] to a desired value
> ISB
> write TTBRx_EL1[ASID] to a desired value
> ISB
>
> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
> Signed-off-by: Christopher Covington <cov@codeaurora.org>
> ---
> arch/arm64/Kconfig | 11 +++++++++++
> arch/arm64/include/asm/cpucaps.h | 3 ++-
> arch/arm64/kernel/cpu_errata.c | 7 +++++++
> arch/arm64/mm/context.c | 10 ++++++++++
> arch/arm64/mm/proc.S | 21 +++++++++++++++++++++
> 5 files changed, 51 insertions(+), 1 deletion(-)

This needs an update to Documentation/arm64/silicon-errata.txt.

> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
> index efcf1f7..f8d94ff 100644
> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -87,6 +87,11 @@ static void flush_context(unsigned int cpu)
> /* Update the list of reserved ASIDs and the ASID bitmap. */
> bitmap_clear(asid_map, 0, NUM_USER_ASIDS);
>
> + /* Reserve ASID '1' for Falkor erratum E1003 */
> + if (IS_ENABLED(CONFIG_QCOM_FALKOR_ERRATUM_E1003) &&
> + cpus_have_cap(ARM64_WORKAROUND_QCOM_FALKOR_E1003))
> + __set_bit(1, asid_map);
> +
> /*
> * Ensure the generation bump is observed before we xchg the
> * active_asids.
> @@ -239,6 +244,11 @@ static int asids_init(void)
> panic("Failed to allocate bitmap for %lu ASIDs\n",
> NUM_USER_ASIDS);
>
> + /* Reserve ASID '1' for Falkor erratum E1003 */
> + if (IS_ENABLED(CONFIG_QCOM_FALKOR_ERRATUM_E1003) &&
> + cpus_have_cap(ARM64_WORKAROUND_QCOM_FALKOR_E1003))
> + __set_bit(1, asid_map);
> +
> pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS);
> return 0;
> }
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 352c73b..b4d6508 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -134,6 +134,27 @@ ENDPROC(cpu_do_resume)
> ENTRY(cpu_do_switch_mm)
> mmid x1, x1 // get mm->context.id
> bfi x0, x1, #48, #16 // set the ASID
> +#ifdef CONFIG_QCOM_FALKOR_ERRATUM_E1003
> +alternative_if_not ARM64_WORKAROUND_QCOM_FALKOR_E1003
> + nop
> + nop
> + nop
> + nop
> + nop
> + nop
> + nop
> + nop
> +alternative_else
> + mrs x2, ttbr0_el1 // get cuurent TTBR0_EL1
> + mov x3, #1 // reserved ASID

It might be best to define a FALCOR_E1003_RESERVED_ASID constant
somewhere, rather than using 1 directly here and in the ASID allocator.

> + bfi x2, x3, #48, #16 // set the reserved ASID + old BADDR
> + msr ttbr0_el1, x2 // update TTBR0_EL1
> + isb
> + bfi x2, x0, #0, #48 // set the desired BADDR + reserved ASID
> + msr ttbr0_el1, x2 // update TTBR0_EL1
> + isb
> +alternative_endif

Please use alternative_if and alternative_else_nop_endif.

As Catalin noted, there are issues with stale and/or conflicting TLB
entries allocated with the reserved ASID, so we likely have to
invalidate that after the final switch.

Thanks,
Mark.