From: Dave Martin <Dave.Martin@arm.com> To: Szabolcs Nagy <szabolcs.nagy@arm.com> Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, "Mark Rutland" <mark.rutland@arm.com>, libc-alpha@sourceware.org, "Ard Biesheuvel" <ard.biesheuvel@linaro.org>, "Catalin Marinas" <catalin.marinas@arm.com>, "Will Deacon" <will.deacon@arm.com>, "Richard Sandiford" <richard.sandiford@arm.com> Subject: Re: [PATCH v2 26/28] arm64/sve: Add documentation Date: Thu, 5 Oct 2017 18:02:54 +0100 [thread overview] Message-ID: <20171005170254.GY3611@e103592.cambridge.arm.com> (raw) In-Reply-To: <59D6603C.2040603@arm.com> On Thu, Oct 05, 2017 at 05:39:24PM +0100, Szabolcs Nagy wrote: > On 31/08/17 18:00, Dave Martin wrote: [...] > > + PR_SVE_SET_VL_ONEXEC > > + > > + Defer the requested vector length change until the next execve(). > > + This allows launching of a new program with a different vector > > + length, while avoiding runtime side effects in the caller. > > + > > + This also overrides the effect of PR_SVE_SET_VL_INHERIT for the > > + first execve(). > > + > > + Without PR_SVE_SET_VL_ONEXEC, any outstanding deferred vector > > + length change is cancelled. > > + > > based on later text it seems this works if exeve is > called in the same thread as prctl was called in. > > this is a bit weird from user-space pov so it may > make sense to state it here explicitly. True. Looking at the prctl(2) man page it looks like other per-thread properties are inherited across execve() in a similar way, but it's at least worth a mention. PR_SET_SECCOMP seems to work like this, for example. So, the intention is that you do a prctl(...ONEXEC) in the run up to execve(), rather than doing it at other random times. The primary reason for ONEXEC is to avoid the side-effects of actually changing the VL. Looking at this though... I wonder whether PR_SVE_SET_VL(... PR_SVE_SET_VL_ONEXEC) should return the VL set for exec, rather than the current VL (which is unchanged by definition in this case, thus uninteresting). This would allow the ONEXEC flag to be used to probe for available VLs without the other side-effects of changing VL, something like: int old = prctl(PR_SVE_GET_VL); int ret; ret = prctl(PR_SVE_SET_VL, 144 | PR_SVE_SET_VL_ONEXEC); if (ret == -1) { perror("PR_SVE_SET_VL"); goto error; } if ((ret & PR_SVE_VL_LEN_MASK) == 144) have_vl_144 = true; if (prctl(PR_SVE_SET_VL, old | PR_SVE_SET_VL_ONEXEC) == -1) { perror("PR_SVE_SET_VL"); goto error; } This does _not_ do the expected thing right now, since there's no direct way to retrieve thread.sve_vl_onexec directly from the kernel (and it didn't really seem justified to add one). Thoughts? Cheers ---Dave
WARNING: multiple messages have this Message-ID (diff)
From: Dave.Martin@arm.com (Dave Martin) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 26/28] arm64/sve: Add documentation Date: Thu, 5 Oct 2017 18:02:54 +0100 [thread overview] Message-ID: <20171005170254.GY3611@e103592.cambridge.arm.com> (raw) In-Reply-To: <59D6603C.2040603@arm.com> On Thu, Oct 05, 2017 at 05:39:24PM +0100, Szabolcs Nagy wrote: > On 31/08/17 18:00, Dave Martin wrote: [...] > > + PR_SVE_SET_VL_ONEXEC > > + > > + Defer the requested vector length change until the next execve(). > > + This allows launching of a new program with a different vector > > + length, while avoiding runtime side effects in the caller. > > + > > + This also overrides the effect of PR_SVE_SET_VL_INHERIT for the > > + first execve(). > > + > > + Without PR_SVE_SET_VL_ONEXEC, any outstanding deferred vector > > + length change is cancelled. > > + > > based on later text it seems this works if exeve is > called in the same thread as prctl was called in. > > this is a bit weird from user-space pov so it may > make sense to state it here explicitly. True. Looking at the prctl(2) man page it looks like other per-thread properties are inherited across execve() in a similar way, but it's at least worth a mention. PR_SET_SECCOMP seems to work like this, for example. So, the intention is that you do a prctl(...ONEXEC) in the run up to execve(), rather than doing it at other random times. The primary reason for ONEXEC is to avoid the side-effects of actually changing the VL. Looking at this though... I wonder whether PR_SVE_SET_VL(... PR_SVE_SET_VL_ONEXEC) should return the VL set for exec, rather than the current VL (which is unchanged by definition in this case, thus uninteresting). This would allow the ONEXEC flag to be used to probe for available VLs without the other side-effects of changing VL, something like: int old = prctl(PR_SVE_GET_VL); int ret; ret = prctl(PR_SVE_SET_VL, 144 | PR_SVE_SET_VL_ONEXEC); if (ret == -1) { perror("PR_SVE_SET_VL"); goto error; } if ((ret & PR_SVE_VL_LEN_MASK) == 144) have_vl_144 = true; if (prctl(PR_SVE_SET_VL, old | PR_SVE_SET_VL_ONEXEC) == -1) { perror("PR_SVE_SET_VL"); goto error; } This does _not_ do the expected thing right now, since there's no direct way to retrieve thread.sve_vl_onexec directly from the kernel (and it didn't really seem justified to add one). Thoughts? Cheers ---Dave
next prev parent reply other threads:[~2017-10-05 17:02 UTC|newest] Thread overview: 224+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-08-31 17:00 [PATCH v2 00/28] ARM Scalable Vector Extension (SVE) Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 01/28] regset: Add support for dynamically sized regsets Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 02/28] arm64: KVM: Hide unsupported AArch64 CPU features from guests Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 14:37 ` Alex Bennée 2017-09-13 14:37 ` Alex Bennée 2017-09-13 14:37 ` Alex Bennée 2017-09-15 0:04 ` Dave Martin 2017-09-15 0:04 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 03/28] arm64: efi: Add missing Kconfig dependency on KERNEL_MODE_NEON Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 04/28] arm64: Port deprecated instruction emulation to new sysctl interface Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 05/28] arm64: fpsimd: Simplify uses of {set,clear}_ti_thread_flag() Dave Martin 2017-08-31 17:00 ` [PATCH v2 05/28] arm64: fpsimd: Simplify uses of {set, clear}_ti_thread_flag() Dave Martin 2017-08-31 17:00 ` [PATCH v2 06/28] arm64/sve: System register and exception syndrome definitions Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 14:48 ` Alex Bennée 2017-09-13 14:48 ` Alex Bennée 2017-09-13 14:48 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 07/28] arm64/sve: Low-level SVE architectural state manipulation functions Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 15:39 ` Alex Bennée 2017-09-13 15:39 ` Alex Bennée 2017-09-13 15:39 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 08/28] arm64/sve: Kconfig update and conditional compilation support Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 09/28] arm64/sve: Signal frame and context structure definition Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 13:36 ` Catalin Marinas 2017-09-13 13:36 ` Catalin Marinas 2017-09-13 21:33 ` Dave Martin 2017-09-13 21:33 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 10/28] arm64/sve: Low-level CPU setup Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 13:32 ` Catalin Marinas 2017-09-13 13:32 ` Catalin Marinas 2017-09-13 19:21 ` Dave Martin 2017-09-13 19:21 ` Dave Martin 2017-09-13 19:21 ` Dave Martin 2017-10-05 10:47 ` Dave Martin 2017-10-05 10:47 ` Dave Martin 2017-10-05 11:04 ` Suzuki K Poulose 2017-10-05 11:04 ` Suzuki K Poulose 2017-10-05 11:22 ` Dave Martin 2017-10-05 11:22 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 11/28] arm64/sve: Core task context handling Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 14:33 ` Catalin Marinas 2017-09-13 14:33 ` Catalin Marinas 2017-09-14 19:55 ` Dave Martin 2017-09-14 19:55 ` Dave Martin 2017-09-20 13:58 ` Catalin Marinas 2017-09-20 13:58 ` Catalin Marinas 2017-10-03 11:11 ` Dave Martin 2017-10-03 11:11 ` Dave Martin 2017-10-04 17:29 ` Catalin Marinas 2017-10-04 17:29 ` Catalin Marinas 2017-10-03 11:33 ` Dave Martin 2017-10-03 11:33 ` Dave Martin 2017-10-05 11:28 ` Catalin Marinas 2017-10-05 11:28 ` Catalin Marinas 2017-10-06 13:10 ` Dave Martin 2017-10-06 13:10 ` Dave Martin 2017-10-06 13:36 ` Catalin Marinas 2017-10-06 13:36 ` Catalin Marinas 2017-10-06 15:15 ` Dave Martin 2017-10-06 15:15 ` Dave Martin 2017-10-06 15:33 ` Catalin Marinas 2017-10-06 15:33 ` Catalin Marinas 2017-09-13 17:26 ` Catalin Marinas 2017-09-13 17:26 ` Catalin Marinas 2017-09-13 19:17 ` Dave Martin 2017-09-13 19:17 ` Dave Martin 2017-09-13 22:21 ` Catalin Marinas 2017-09-13 22:21 ` Catalin Marinas 2017-09-14 19:40 ` Dave Martin 2017-09-14 19:40 ` Dave Martin 2017-09-19 17:13 ` Catalin Marinas 2017-09-19 17:13 ` Catalin Marinas 2017-08-31 17:00 ` [PATCH v2 12/28] arm64/sve: Support vector length resetting for new processes Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 8:47 ` Alex Bennée 2017-09-14 8:47 ` Alex Bennée 2017-09-14 8:47 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 13/28] arm64/sve: Signal handling support Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 9:30 ` Alex Bennée 2017-09-14 9:30 ` Alex Bennée 2017-09-14 9:30 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-13 17:29 ` Catalin Marinas 2017-09-13 17:29 ` Catalin Marinas 2017-09-13 19:06 ` Dave Martin 2017-09-13 19:06 ` Dave Martin 2017-09-13 22:11 ` Catalin Marinas 2017-09-13 22:11 ` Catalin Marinas 2017-10-05 16:42 ` Dave Martin 2017-10-05 16:42 ` Dave Martin 2017-10-05 16:53 ` Catalin Marinas 2017-10-05 16:53 ` Catalin Marinas 2017-10-05 17:04 ` Dave Martin 2017-10-05 17:04 ` Dave Martin 2017-09-20 10:57 ` Alan Hayward 2017-09-20 10:57 ` Alan Hayward 2017-09-20 10:59 ` Alan Hayward 2017-09-20 10:59 ` Alan Hayward 2017-09-20 11:09 ` Dave Martin 2017-09-20 11:09 ` Dave Martin 2017-09-20 18:08 ` Alan Hayward 2017-09-20 18:08 ` Alan Hayward 2017-09-21 11:19 ` Dave Martin 2017-09-21 11:19 ` Dave Martin 2017-09-21 11:57 ` Alan Hayward 2017-09-21 11:57 ` Alan Hayward 2017-08-31 17:00 ` [PATCH v2 15/28] arm64: cpufeature: Move sys_caps_initialised declarations Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 9:33 ` Alex Bennée 2017-09-14 9:33 ` Alex Bennée 2017-09-14 9:33 ` Alex Bennée 2017-09-14 9:35 ` Suzuki K Poulose 2017-09-14 9:35 ` Suzuki K Poulose 2017-08-31 17:00 ` [PATCH v2 16/28] arm64/sve: Probe SVE capabilities and usable vector lengths Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 9:45 ` Alex Bennée 2017-09-14 9:45 ` Alex Bennée 2017-09-14 9:45 ` Alex Bennée 2017-09-28 14:22 ` Dave Martin 2017-09-28 14:22 ` Dave Martin 2017-09-28 17:32 ` Alex Bennée 2017-09-28 17:32 ` Alex Bennée 2017-09-28 17:32 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 17/28] arm64/sve: Preserve SVE registers around kernel-mode NEON use Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 10:52 ` Alex Bennée 2017-09-14 10:52 ` Alex Bennée 2017-09-14 10:52 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 18/28] arm64/sve: Preserve SVE registers around EFI runtime service calls Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 11:01 ` Alex Bennée 2017-09-14 11:01 ` Alex Bennée 2017-09-14 11:01 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 19/28] arm64/sve: ptrace and ELF coredump support Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-06 16:21 ` Okamoto, Takayuki 2017-09-06 16:21 ` Okamoto, Takayuki 2017-09-06 18:16 ` Dave Martin 2017-09-06 18:16 ` Dave Martin 2017-09-07 5:11 ` Okamoto, Takayuki 2017-09-07 5:11 ` Okamoto, Takayuki 2017-09-07 5:11 ` Okamoto, Takayuki 2017-09-08 13:11 ` Dave Martin 2017-09-08 13:11 ` Dave Martin 2017-09-14 12:57 ` Alex Bennée 2017-09-14 12:57 ` Alex Bennée 2017-09-14 12:57 ` Alex Bennée 2017-09-28 14:57 ` Dave Martin 2017-09-28 14:57 ` Dave Martin 2017-09-29 12:46 ` Dave Martin 2017-09-29 12:46 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 20/28] arm64/sve: Add prctl controls for userspace vector length management Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 13:02 ` Alex Bennée 2017-09-14 13:02 ` Alex Bennée 2017-09-14 13:02 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 21/28] arm64/sve: Add sysctl to set the default vector length for new processes Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 13:05 ` Alex Bennée 2017-09-14 13:05 ` Alex Bennée 2017-09-14 13:05 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 22/28] arm64/sve: KVM: Prevent guests from using SVE Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 13:28 ` Alex Bennée 2017-09-14 13:28 ` Alex Bennée 2017-09-14 13:28 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 23/28] arm64/sve: KVM: Treat guest SVE use as undefined instruction execution Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 13:30 ` Alex Bennée 2017-09-14 13:30 ` Alex Bennée 2017-09-14 13:30 ` Alex Bennée 2017-09-14 13:31 ` Alex Bennée 2017-09-14 13:31 ` Alex Bennée 2017-09-14 13:31 ` Alex Bennée 2017-09-29 13:00 ` Dave Martin 2017-09-29 13:00 ` Dave Martin 2017-09-29 14:43 ` Alex Bennée 2017-09-29 14:43 ` Alex Bennée 2017-09-29 14:43 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 24/28] arm64/sve: KVM: Hide SVE from CPU features exposed to guests Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-09-14 13:32 ` Alex Bennée 2017-09-14 13:32 ` Alex Bennée 2017-09-14 13:32 ` Alex Bennée 2017-08-31 17:00 ` [PATCH v2 25/28] arm64/sve: Detect SVE and activate runtime support Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` [PATCH v2 26/28] arm64/sve: Add documentation Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-10-05 16:39 ` Szabolcs Nagy 2017-10-05 16:39 ` Szabolcs Nagy 2017-10-05 17:02 ` Dave Martin [this message] 2017-10-05 17:02 ` Dave Martin 2017-10-06 15:43 ` Szabolcs Nagy 2017-10-06 15:43 ` Szabolcs Nagy 2017-10-06 17:37 ` Dave Martin 2017-10-06 17:37 ` Dave Martin 2017-10-09 9:34 ` Alex Bennée 2017-10-09 9:34 ` Alex Bennée 2017-10-09 9:34 ` Alex Bennée 2017-10-09 9:49 ` Dave Martin 2017-10-09 9:49 ` Dave Martin 2017-10-09 14:07 ` Alex Bennée 2017-10-09 14:07 ` Alex Bennée 2017-10-09 14:07 ` Alex Bennée 2017-10-09 16:20 ` Dave Martin 2017-10-09 16:20 ` Dave Martin 2017-08-31 17:00 ` [RFC PATCH v2 27/28] arm64: signal: Report signal frame size to userspace via auxv Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:00 ` Dave Martin 2017-08-31 17:01 ` [RFC PATCH v2 28/28] arm64/sve: signal: Include SVE when computing AT_MINSIGSTKSZ Dave Martin 2017-08-31 17:01 ` Dave Martin
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