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SubjectRe: [PATCH v3 2/4] arm64: mte: Add asynchronous mode support
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On 1/15/21 3:13 PM, Mark Rutland wrote:
> On Fri, Jan 15, 2021 at 12:00:41PM +0000, Vincenzo Frascino wrote:
>> MTE provides an asynchronous mode for detecting tag exceptions. In
>> particular instead of triggering a fault the arm64 core updates a
>> register which is checked by the kernel after the asynchronous tag
>> check fault has occurred.
>>
>> Add support for MTE asynchronous mode.
>>
>> The exception handling mechanism will be added with a future patch.
>>
>> Note: KASAN HW activates async mode via kasan.mode kernel parameter.
>> The default mode is set to synchronous.
>> The code that verifies the status of TFSR_EL1 will be added with a
>> future patch.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will@kernel.org>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>> ---
>> arch/arm64/kernel/mte.c | 26 ++++++++++++++++++++++++--
>> 1 file changed, 24 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
>> index 53a6d734e29b..df7a1ae26d7c 100644
>> --- a/arch/arm64/kernel/mte.c
>> +++ b/arch/arm64/kernel/mte.c
>> @@ -153,8 +153,30 @@ void mte_init_tags(u64 max_tag)
>>
>> void mte_enable_kernel(enum kasan_hw_tags_mode mode)
>> {
>> - /* Enable MTE Sync Mode for EL1. */
>> - sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
>> + const char *m;
>> +
>> + /* Preset parameter values based on the mode. */
>> + switch (mode) {
>> + case KASAN_HW_TAGS_ASYNC:
>> + /* Enable MTE Async Mode for EL1. */
>> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_ASYNC);
>> + m = "asynchronous";
>> + break;
>> + case KASAN_HW_TAGS_SYNC:
>> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
>> + m = "synchronous";
>> + break;
>> + default:
>> + /*
>> + * kasan mode should be always set hence we should
>> + * not reach this condition.
>> + */
>> + WARN_ON_ONCE(1);
>> + return;
>> + }
>> +
>> + pr_info_once("MTE: enabled in %s mode at EL1\n", m);
>> +
>> isb();
>> }
>
> For clarity, we should have that ISB before the pr_info_once().
>

Good point, I will fix it in v4.

> As with my comment on patch 1, I think with separate functions this
> would be much clearer and simpler:
>
> static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
> {
> sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
> isb();
>
> pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
> }
>
> void mte_enable_kernel_sync(void)
> {
> __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
> }
>
> void mte_enable_kernel_async(void)
> {
> __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
> }
>

Ok, seems cleaner like this, will adapt my code accordingly.

> Thanks,
> Mark.
>

--
Regards,
Vincenzo

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