From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Wed, 24 May 2017 15:42:44 +0100 Subject: [RFC PATCH v2 0/2] Simplify kernel-mode NEON Message-ID: <1495636986-30515-1-git-send-email-Dave.Martin@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org This series aims to simplify kernel-mode NEON. The main motivation for these changes is that supporting kernel-mode NEON alongside SVE is tricky with the current framework: the current partial save/restore mechanisms would need additional porting to save/restore the extended SVE vector bits, and this renders the cost saving of partial save/restore rather doubtful -- even if not all vector registers are saved, the save/restore cost will still grow with increasing vector length. We could get the mechanics of this to work in principle, but it doesn't feel like the right thing to do. If we withdraw kernel-mode NEON support for hardirq context, accept some extra softirq latency and disable nesting, then we can simplify the code by always saving the task context directly into task_struct and deferring all restore to ret_to_user. Previous discussions with Ard Biesheuvel suggest that this is a feasible approach and reasonably aligned with other architectures. The main impact on client code is that callers must check that kernel-mode NEON is usable in the current context and fall back to a non-NEON when necessary. Ard has already done some work on this. [1] The interesting changes are all in patch 2: the first patch just adds a header inclusion guard that I noted was missing. [1] git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git kernel-mode-neon I've only build-tested so far. Ard, do you have any suggestions for how to test these changes effectively? Cheers ---Dave Dave Martin (2): arm64: neon: Add missing header guard in arm64: neon: Remove support for nested or hardirq kernel-mode NEON arch/arm64/include/asm/fpsimd.h | 14 ----- arch/arm64/include/asm/fpsimdmacros.h | 56 ----------------- arch/arm64/include/asm/neon.h | 12 +++- arch/arm64/include/asm/simd.h | 56 +++++++++++++++++ arch/arm64/kernel/entry-fpsimd.S | 24 ------- arch/arm64/kernel/fpsimd.c | 114 ++++++++++++++++++++++++---------- 6 files changed, 146 insertions(+), 130 deletions(-) create mode 100644 arch/arm64/include/asm/simd.h -- 2.1.4