Re: [PATCH v3 2/5] arm64: Work around Falkor erratum 1003

From: Marc Zyngier
Date: Wed Jan 11 2017 - 13:22:19 EST

On 11/01/17 18:06, Catalin Marinas wrote:
> Some minor comments below, nothing fundamental (as long as you say the
> new sequence doesn't have the speculative TLB load problem I mentioned
> on a previous version).
>
> On Wed, Jan 11, 2017 at 09:41:15AM -0500, Christopher Covington wrote:
>> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
>> index 405da11..7151aed 100644
>> --- a/Documentation/arm64/silicon-errata.txt
>> +++ b/Documentation/arm64/silicon-errata.txt
>> @@ -42,24 +42,25 @@ file acts as a registry of software workarounds in the Linux Kernel and
>> will be updated when new workarounds are committed and backported to
>> stable kernels.
>>
>> -| Implementor | Component | Erratum ID | Kconfig |
>> -+----------------+-----------------+-----------------+-------------------------+
>> -| ARM | Cortex-A53 | #826319 | ARM64_ERRATUM_826319 |
>> -| ARM | Cortex-A53 | #827319 | ARM64_ERRATUM_827319 |
>> -| ARM | Cortex-A53 | #824069 | ARM64_ERRATUM_824069 |
>> -| ARM | Cortex-A53 | #819472 | ARM64_ERRATUM_819472 |
>> -| ARM | Cortex-A53 | #845719 | ARM64_ERRATUM_845719 |
>> -| ARM | Cortex-A53 | #843419 | ARM64_ERRATUM_843419 |
>> -| ARM | Cortex-A57 | #832075 | ARM64_ERRATUM_832075 |
>> -| ARM | Cortex-A57 | #852523 | N/A |
>> -| ARM | Cortex-A57 | #834220 | ARM64_ERRATUM_834220 |
>> -| ARM | Cortex-A72 | #853709 | N/A |
>> -| ARM | MMU-500 | #841119,#826419 | N/A |
>> -| | | | |
>> -| Cavium | ThunderX ITS | #22375, #24313 | CAVIUM_ERRATUM_22375 |
>> -| Cavium | ThunderX ITS | #23144 | CAVIUM_ERRATUM_23144 |
>> -| Cavium | ThunderX GICv3 | #23154 | CAVIUM_ERRATUM_23154 |
>> -| Cavium | ThunderX Core | #27456 | CAVIUM_ERRATUM_27456 |
>> -| Cavium | ThunderX SMMUv2 | #27704 | N/A |
>> -| | | | |
>> -| Freescale/NXP | LS2080A/LS1043A | A-008585 | FSL_ERRATUM_A008585 |
>> +| Implementor | Component | Erratum ID | Kconfig |
>> ++---------------+-----------------+-----------------+--------------------------+
>> +| ARM | Cortex-A53 | #826319 | ARM64_ERRATUM_826319 |
>> +| ARM | Cortex-A53 | #827319 | ARM64_ERRATUM_827319 |
>> +| ARM | Cortex-A53 | #824069 | ARM64_ERRATUM_824069 |
>> +| ARM | Cortex-A53 | #819472 | ARM64_ERRATUM_819472 |
>> +| ARM | Cortex-A53 | #845719 | ARM64_ERRATUM_845719 |
>> +| ARM | Cortex-A53 | #843419 | ARM64_ERRATUM_843419 |
>> +| ARM | Cortex-A57 | #832075 | ARM64_ERRATUM_832075 |
>> +| ARM | Cortex-A57 | #852523 | N/A |
>> +| ARM | Cortex-A57 | #834220 | ARM64_ERRATUM_834220 |
>> +| ARM | Cortex-A72 | #853709 | N/A |
>> +| ARM | MMU-500 | #841119,#826419 | N/A |
>> +| | | | |
>> +| Cavium | ThunderX ITS | #22375, #24313 | CAVIUM_ERRATUM_22375 |
>> +| Cavium | ThunderX ITS | #23144 | CAVIUM_ERRATUM_23144 |
>> +| Cavium | ThunderX GICv3 | #23154 | CAVIUM_ERRATUM_23154 |
>> +| Cavium | ThunderX Core | #27456 | CAVIUM_ERRATUM_27456 |
>> +| Cavium | ThunderX SMMUv2 | #27704 | N/A |
>> +| | | | |
>> +| Freescale/NXP | LS2080A/LS1043A | A-008585 | FSL_ERRATUM_A008585 |
>> +| Qualcomm | Falkor v1 | E1003 | QCOM_FALKOR_ERRATUM_1003 |
>
> Please don't change the "Implementor" column width, there is no point
> and it makes the patch harder to read (i.e. this hunk should only have
> one line).
>
>> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
>> index 4c63cb1..5a0a82a 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 for Falkor erratum 1003 */
>> + if (IS_ENABLED(CONFIG_QCOM_FALKOR_ERRATUM_1003) &&
>> + cpus_have_cap(ARM64_WORKAROUND_QCOM_FALKOR_E1003))
>> + __set_bit(FALKOR_RESERVED_ASID, asid_map);
>> +
>> /*
>> * Ensure the generation bump is observed before we xchg the
>> * active_asids.
>> @@ -244,6 +249,11 @@ static int asids_init(void)
>> panic("Failed to allocate bitmap for %lu ASIDs\n",
>> NUM_USER_ASIDS);
>>
>> + /* Reserve ASID for Falkor erratum 1003 */
>> + if (IS_ENABLED(CONFIG_QCOM_FALKOR_ERRATUM_1003) &&
>> + cpus_have_cap(ARM64_WORKAROUND_QCOM_FALKOR_E1003))
>> + __set_bit(FALKOR_RESERVED_ASID, asid_map);
>> +
>> pr_info("ASID allocator initialised with %lu entries\n", NUM_USER_ASIDS);
>> return 0;
>> }
>
> You could as well write a small static function in this file and call it
> twice.
>
>> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
>> index 32682be..9ee46df 100644
>> --- a/arch/arm64/mm/proc.S
>> +++ b/arch/arm64/mm/proc.S
>> @@ -23,6 +23,7 @@
>> #include <asm/assembler.h>
>> #include <asm/asm-offsets.h>
>> #include <asm/hwcap.h>
>> +#include <asm/mmu_context.h>
>> #include <asm/pgtable.h>
>> #include <asm/pgtable-hwdef.h>
>> #include <asm/cpufeature.h>
>> @@ -140,6 +141,18 @@ 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_1003
>> +alternative_if ARM64_WORKAROUND_QCOM_FALKOR_E1003
>> + mrs x2, ttbr0_el1
>> + mov x3, #FALKOR_RESERVED_ASID
>> + bfi x2, x3, #48, #16 // reserved ASID + old BADDR
>> + msr ttbr0_el1, x2
>> + isb
>> + bfi x2, x0, #0, #48 // reserved ASID + new BADDR
>> + msr ttbr0_el1, x2
>> + isb
>> +alternative_else_nop_endif
>> +#endif
>> msr ttbr0_el1, x0 // set TTBR0
>> isb
>> post_ttbr0_update_workaround
>
> Please move the above hunk to a pre_ttbr0_update_workaround macro for
> consistency with post_ttbr0_update_workaround.

In which case (and also for consistency), should we add that pre_ttbr0
macro to entry.S, just before __uaccess_ttbr0_enable? It may not be
needed in the SW pan case, but it is probably worth entertaining the
idea that there may be something to do there...

Thanks,

M.
--
Jazz is not dead. It just smells funny...