From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Thu, 21 Sep 2017 12:19:45 +0100 Subject: [PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length In-Reply-To: References: <1504198860-12951-1-git-send-email-Dave.Martin@arm.com> <1504198860-12951-15-git-send-email-Dave.Martin@arm.com> <20170920110902.GG24231@e103592.cambridge.arm.com> Message-ID: <20170921111937.GA17434@e103592.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Sep 20, 2017 at 06:08:21PM +0000, Alan Hayward wrote: > > > On 20 Sep 2017, at 12:09, Dave Martin wrote: [...] > >> Given, sve_set_vector_length is called when setting the vector length in > >> PTRACE_SETREGSET, it looks to me like if you set VL to a value that?s not > >> supported by the hardware, then it?s going to round down to the previous value. > >> Is that correct? I?m not sure if that?s explained in the docs? > > > > Does this cover it? > > > > "On success, the calling thread's vector length is changed to the > > largest value supported by the system that is less than or equal to vl." > > > > (For ptrace, I just cross-reference the PR_SVE_SET_VL behaviour, above.) > > For ptrace is it worth mentioning user should do a GET after a SET to confirm > what VL value was actually set? This seems worth a clarification -- I'd thought this was already mentioned, but it isn't. How about: The caller must make a further GETREGSET call if it needs to know what VL is actually set by SETREGSET, unless is it known in advance that the requested VL is supported. [...] Cheers ---Dave