From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>,
Marco Elver <elver@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Evgenii Stepanov <eugenis@google.com>,
Will Deacon <will.deacon@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Alexander Potapenko <glider@google.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH 2/4] arm64: mte: Add asynchronous mode support
Date: Thu, 7 Jan 2021 17:29:24 +0000 [thread overview]
Message-ID: <c4f04127-a682-d809-1dad-5ee1f51d3e0a@arm.com> (raw)
In-Reply-To: <CAAeHK+xuGRzkLdrfGZVo-RVfkH31qUrNdBaPd4k5ffMKHWGfTQ@mail.gmail.com>
Hi Andrey,
On 1/7/21 4:29 PM, Andrey Konovalov wrote:
> On Wed, Jan 6, 2021 at 12:56 PM Vincenzo Frascino
> <vincenzo.frascino@arm.com> 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 at the first entry after the tag
>> exception 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.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>> ---
>> arch/arm64/kernel/mte.c | 31 +++++++++++++++++++++++++++++--
>> 1 file changed, 29 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
>> index 24a273d47df1..5d992e16b420 100644
>> --- a/arch/arm64/kernel/mte.c
>> +++ b/arch/arm64/kernel/mte.c
>> @@ -153,8 +153,35 @@ void mte_init_tags(u64 max_tag)
>>
>> void mte_enable_kernel(enum kasan_arg_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_ARG_MODE_OFF:
>> + return;
>> + case KASAN_ARG_MODE_LIGHT:
>> + /* Enable MTE Async Mode for EL1. */
>> + sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_ASYNC);
>> + m = "asynchronous";
>> + break;
>> + case KASAN_ARG_MODE_DEFAULT:
>> + case KASAN_ARG_MODE_PROD:
>> + case KASAN_ARG_MODE_FULL:
>> + /* Enable MTE Sync Mode for EL1. */
>> + 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();
>> }
>>
>> --
>> 2.29.2
>>
>
> Hi Vincenzo,
>
> It would be cleaner to pass a bool to mte_enable_kernel() and have it
> indicate sync/async mode. This way you don't have to pull all these
> KASAN constants into the arm64 code.
>
Boolean arguments are generally bad for legibility, hence I tend to avoid them.
In this case exposing the constants does not seem a big issue especially because
the only user of this code is "KASAN_HW_TAGS" and definitely improves its
legibility hence I would prefer to keep it as is.
> Thanks!
>
--
Regards,
Vincenzo
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next prev parent reply other threads:[~2021-01-07 17:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 11:55 [PATCH 0/4] arm64: ARMv8.5-A: MTE: Add async mode support Vincenzo Frascino
2021-01-06 11:55 ` [PATCH 1/4] kasan, arm64: Add KASAN light mode Vincenzo Frascino
2021-01-06 11:55 ` [PATCH 2/4] arm64: mte: Add asynchronous mode support Vincenzo Frascino
2021-01-07 16:29 ` Andrey Konovalov
2021-01-07 17:29 ` Vincenzo Frascino [this message]
2021-01-07 19:18 ` Andrey Konovalov
2021-01-08 10:48 ` Vincenzo Frascino
2021-01-08 13:36 ` Andrey Konovalov
2021-01-08 17:26 ` Vincenzo Frascino
2021-01-06 11:55 ` [PATCH 3/4] arm64: mte: Enable async tag check fault Vincenzo Frascino
2021-01-06 15:01 ` kernel test robot
2021-01-06 11:55 ` [PATCH 4/4] arm64: mte: Optimize mte_assign_mem_tag_range() Vincenzo Frascino
2021-01-06 16:35 ` [PATCH 0/4] arm64: ARMv8.5-A: MTE: Add async mode support Vincenzo Frascino
2021-01-06 16:42 ` Will Deacon
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