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From: Florian Weimer <fweimer@redhat.com>
To: Peter Bergner <bergner@oss.tenstorrent.com>
Cc: "Andy Chiu" <tchiu@tenstorrent.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Shuah Khan" <skhan@linuxfoundation.org>,
	"Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org,
	kito.cheng@sifive.com, dfustini@oss.tenstorrent.com,
	greentime.hu@sifive.com,
	"Andrew Jones" <andrew.jones@oss.qualcomm.com>,
	"Nutty Liu" <nutty.liu@hotmail.com>,
	"Pincheng Wang" <pincheng.plct@isrc.iscas.ac.cn>,
	"Yao Zihong" <zihong.plct@isrc.iscas.ac.cn>,
	"Xu Lu" <luxu.kernel@bytedance.com>,
	"Aleksa Paunovic" <aleksa.paunovic@htecgroup.com>,
	"Jingwei Wang" <wangjingwei@iscas.ac.cn>,
	"Zong Li" <zong.li@sifive.com>,
	"Deepak Gupta" <debug@rivosinc.com>,
	"Clément Léger" <cleger@rivosinc.com>,
	linux-api@vger.kernel.org,
	"Jeffrey Law" <jeffrey.law@oss.qualcomm.com>
Subject: Re: [EXT] Re: [PATCH 1/2] riscv: hwprobe: export the availability of vector to user
Date: Thu, 06 Aug 2026 08:31:48 +0200	[thread overview]
Message-ID: <lhuik5n4v57.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <cc671848-f954-41bf-b7a9-ba34c29593ec@oss.tenstorrent.com> (Peter Bergner's message of "Wed, 5 Aug 2026 13:40:27 -0500")

* Peter Bergner:

>> We only get a true userspace simplification over hwprobe + prctl if we
>> can disable vector extension usage if the kernel does not support
>> RISCV_HWPROBE_KEY_EXT_ENABLED (so a V usage regression for older
>> kernels).  Otherwise we'd have to use the new approach and, as a
>> fallback, the old combination of hwprobe and prctl.
>
> Since the kernel ignores unknown keys, we do get a userspace simplification
> over hwprobe + prctl.  The plan is for our GLIBC IFUNC resolvers to just have
> one hwprobe call (as they do now) with RISCV_HWPROBE_KEY_EXT_ENABLED as the
> first key and RISCV_HWPROBE_KEY_IMA_EXT_0 as the second key.

And if RISCV_HWPROBE_KEY_IMA_EXT_0 comes back at -1, we'd turn on V
unconditionally?  That still leaves the existing bug on old kernels, but
at least the bug goes away with a kernel upgrade.  This isn't too bad.

Thanks,
Florian


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  reply	other threads:[~2026-08-06  6:32 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-07-23 22:20 [PATCH 0/2] riscv: hwprobe: report per-process extension availability Andy Chiu
2026-07-23 22:20 ` [PATCH 1/2] riscv: hwprobe: export the availability of vector to user Andy Chiu
2026-07-24 12:53   ` Florian Weimer
2026-08-05 18:40     ` [EXT] " Peter Bergner
2026-08-06  6:31       ` Florian Weimer [this message]
2026-08-06 17:09         ` Peter Bergner
2026-07-23 22:20 ` [PATCH 2/2] selftests: riscv: hwprobe: test the RISCV_HWPROBE_KEY_EXT_ENABLED modifier Andy Chiu

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