Re: [RFC PATCH 0/2] kasan: hw_tags: Add option to tag only at allocation time

[Harry Yoo <harry@kernel.org>]

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On 6/19/26 10:04 PM, Catalin Marinas wrote:
> On Thu, Jun 18, 2026 at 11:05:43PM +0900, Harry Yoo wrote:
>> On 6/18/26 10:35 PM, Harry Yoo wrote:
>>> On 6/12/26 1:44 PM, Dev Jain wrote:
>>>> Introduce a boot option to tag only at allocation time of the objects. This
>>>> reduces KASAN MTE overhead, the tradeoff being reduced ability of
>>>> catching bugs.
>>>
>>> I think most of overhead when enabling MTE comes from loading and
>>> validing tags for every memory access (either in SYNC or ASYNC mode),
>>> rather than from storing tags.
>>
>> Is there any reason not to use STGM instead of STG + DC GVA when
>> setting/clearing tags for large sizes when we know they are properly
>> aligned?
> 
> STGM is intended for copying tags when paired with LDGM. Have you seen
> hardware where STGM is faster than STG or DC GVA?

No, I haven't. It was a question I had after learning that there are
multiple ways to store tags ;)

> For properly aligned
> buffers, I'd expect DC GVA to behave at least on par with STGM.

Thanks for answering!

-- 
Cheers,
Harry / Hyeonggon

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