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Thu, 6 Aug 2026 06:31:59 +0000 (UTC) Received: from fweimer-oldenburg.csb.redhat.com (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E85001956049; Thu, 6 Aug 2026 06:31:50 +0000 (UTC) From: Florian Weimer To: Peter Bergner Cc: Andy Chiu , Jonathan Corbet , Shuah Khan , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org, kito.cheng@sifive.com, dfustini@oss.tenstorrent.com, greentime.hu@sifive.com, Andrew Jones , Nutty Liu , Pincheng Wang , Yao Zihong , Xu Lu , Aleksa Paunovic , Jingwei Wang , Zong Li , Deepak Gupta , =?utf-8?Q?Cl=C3=A9ment_L=C3=A9ger?= , linux-api@vger.kernel.org, Jeffrey Law Subject: Re: [EXT] Re: [PATCH 1/2] riscv: hwprobe: export the availability of vector to user In-Reply-To: (Peter Bergner's message of "Wed, 5 Aug 2026 13:40:27 -0500") References: <20260723222109.2229089-1-tchiu@tenstorrent.com> <20260723222109.2229089-2-tchiu@tenstorrent.com> <87bjbwk0q5.fsf@oldenburg.str.redhat.com> Date: Thu, 06 Aug 2026 08:31:48 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-MFC-PROC-ID: 28zduI8tfE3yEJQJTASdkJkh2gAC8AqLp9gGNhRwY9E_1785997921 X-Mimecast-Originator: redhat.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260806_073221_091273_D323D173 X-CRM114-Status: GOOD ( 11.26 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org * 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 _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv