From: Dave Martin <Dave.Martin@arm.com> To: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: linux-crypto@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>, herbert@gondor.apana.org.au, Peter Zijlstra <peterz@infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Will Deacon <will.deacon@arm.com>, Russell King - ARM Linux <linux@armlinux.org.uk>, Steven Rostedt <rostedt@goodmis.org>, Thomas Gleixner <tglx@linutronix.de>, linux-arm-kernel@lists.infradead.org, linux-rt-users@vger.kernel.org Subject: Re: [PATCH v3 11/20] arm64: assembler: add macros to conditionally yield the NEON under PREEMPT Date: Thu, 7 Dec 2017 14:39:34 +0000 [thread overview] Message-ID: <20171207143934.GF22781@e103592.cambridge.arm.com> (raw) In-Reply-To: <20171206194346.24393-12-ard.biesheuvel@linaro.org> On Wed, Dec 06, 2017 at 07:43:37PM +0000, Ard Biesheuvel wrote: > Add support macros to conditionally yield the NEON (and thus the CPU) > that may be called from the assembler code. > > In some cases, yielding the NEON involves saving and restoring a non > trivial amount of context (especially in the CRC folding algorithms), > and so the macro is split into three, and the code in between is only > executed when the yield path is taken, allowing the context to be preserved. > The third macro takes an optional label argument that marks the resume > path after a yield has been performed. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm64/include/asm/assembler.h | 51 ++++++++++++++++++++ > 1 file changed, 51 insertions(+) > > diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h > index 5f61487e9f93..c54e408fd5a7 100644 > --- a/arch/arm64/include/asm/assembler.h > +++ b/arch/arm64/include/asm/assembler.h > @@ -572,4 +572,55 @@ alternative_else_nop_endif > #endif > .endm > > +/* > + * Check whether to yield to another runnable task from kernel mode NEON code > + * (which runs with preemption disabled). > + * > + * if_will_cond_yield_neon > + * // pre-yield patchup code > + * do_cond_yield_neon > + * // post-yield patchup code > + * endif_yield_neon ^ Mention the lbl argument? > + * > + * - Check whether the preempt count is exactly 1, in which case disabling enabling ^ > + * preemption once will make the task preemptible. If this is not the case, > + * yielding is pointless. > + * - Check whether TIF_NEED_RESCHED is set, and if so, disable and re-enable > + * kernel mode NEON (which will trigger a reschedule), and branch to the > + * yield fixup code. Mention that neither patchup sequence is allowed to use section-changing directives? For example: if_will_cond_yield_neon // some code .pushsection .rodata, "a" foo: .quad // some literal data for some reason .popsection // some code do_cond_yield_neon is not safe, because .previous is now .rodata. (You could protect against this with .pushsection .text; .previous; .subsection 1; // ... .popsection but it may be overkill.) > + * > + * This macro sequence clobbers x0, x1 and the flags register unconditionally, > + * and may clobber x2 .. x18 if the yield path is taken. > + */ > + > + .macro cond_yield_neon, lbl > + if_will_cond_yield_neon > + do_cond_yield_neon > + endif_yield_neon \lbl > + .endm > + > + .macro if_will_cond_yield_neon > +#ifdef CONFIG_PREEMPT > + get_thread_info x0 > + ldr w1, [x0, #TSK_TI_PREEMPT] > + ldr x0, [x0, #TSK_TI_FLAGS] > + cmp w1, #1 // == PREEMPT_OFFSET Can we at least drop a BUILD_BUG_ON() somewhere to check this? Maybe in kernel_neon_begin() since this is intimately kernel-mode NEON related. > + csel x0, x0, xzr, eq > + tbnz x0, #TIF_NEED_RESCHED, 5555f // needs rescheduling? > +#endif A comment that we will fall through to 6666f here may be helpful. > + .subsection 1 > +5555: > + .endm > + > + .macro do_cond_yield_neon > + bl kernel_neon_end > + bl kernel_neon_begin > + .endm > + > + .macro endif_yield_neon, lbl=6666f > + b \lbl > + .previous > +6666: Could have slightly more random "random" labels here, but otherwise it looks ok to me. I might go through and replace all the random labels with something more robust sometime, but I've never been sure it was worth the effort... 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 v3 11/20] arm64: assembler: add macros to conditionally yield the NEON under PREEMPT Date: Thu, 7 Dec 2017 14:39:34 +0000 [thread overview] Message-ID: <20171207143934.GF22781@e103592.cambridge.arm.com> (raw) In-Reply-To: <20171206194346.24393-12-ard.biesheuvel@linaro.org> On Wed, Dec 06, 2017 at 07:43:37PM +0000, Ard Biesheuvel wrote: > Add support macros to conditionally yield the NEON (and thus the CPU) > that may be called from the assembler code. > > In some cases, yielding the NEON involves saving and restoring a non > trivial amount of context (especially in the CRC folding algorithms), > and so the macro is split into three, and the code in between is only > executed when the yield path is taken, allowing the context to be preserved. > The third macro takes an optional label argument that marks the resume > path after a yield has been performed. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm64/include/asm/assembler.h | 51 ++++++++++++++++++++ > 1 file changed, 51 insertions(+) > > diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h > index 5f61487e9f93..c54e408fd5a7 100644 > --- a/arch/arm64/include/asm/assembler.h > +++ b/arch/arm64/include/asm/assembler.h > @@ -572,4 +572,55 @@ alternative_else_nop_endif > #endif > .endm > > +/* > + * Check whether to yield to another runnable task from kernel mode NEON code > + * (which runs with preemption disabled). > + * > + * if_will_cond_yield_neon > + * // pre-yield patchup code > + * do_cond_yield_neon > + * // post-yield patchup code > + * endif_yield_neon ^ Mention the lbl argument? > + * > + * - Check whether the preempt count is exactly 1, in which case disabling enabling ^ > + * preemption once will make the task preemptible. If this is not the case, > + * yielding is pointless. > + * - Check whether TIF_NEED_RESCHED is set, and if so, disable and re-enable > + * kernel mode NEON (which will trigger a reschedule), and branch to the > + * yield fixup code. Mention that neither patchup sequence is allowed to use section-changing directives? For example: if_will_cond_yield_neon // some code .pushsection .rodata, "a" foo: .quad // some literal data for some reason .popsection // some code do_cond_yield_neon is not safe, because .previous is now .rodata. (You could protect against this with .pushsection .text; .previous; .subsection 1; // ... .popsection but it may be overkill.) > + * > + * This macro sequence clobbers x0, x1 and the flags register unconditionally, > + * and may clobber x2 .. x18 if the yield path is taken. > + */ > + > + .macro cond_yield_neon, lbl > + if_will_cond_yield_neon > + do_cond_yield_neon > + endif_yield_neon \lbl > + .endm > + > + .macro if_will_cond_yield_neon > +#ifdef CONFIG_PREEMPT > + get_thread_info x0 > + ldr w1, [x0, #TSK_TI_PREEMPT] > + ldr x0, [x0, #TSK_TI_FLAGS] > + cmp w1, #1 // == PREEMPT_OFFSET Can we at least drop a BUILD_BUG_ON() somewhere to check this? Maybe in kernel_neon_begin() since this is intimately kernel-mode NEON related. > + csel x0, x0, xzr, eq > + tbnz x0, #TIF_NEED_RESCHED, 5555f // needs rescheduling? > +#endif A comment that we will fall through to 6666f here may be helpful. > + .subsection 1 > +5555: > + .endm > + > + .macro do_cond_yield_neon > + bl kernel_neon_end > + bl kernel_neon_begin > + .endm > + > + .macro endif_yield_neon, lbl=6666f > + b \lbl > + .previous > +6666: Could have slightly more random "random" labels here, but otherwise it looks ok to me. I might go through and replace all the random labels with something more robust sometime, but I've never been sure it was worth the effort... Cheers ---Dave
next prev parent reply other threads:[~2017-12-07 14:39 UTC|newest] Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-12-06 19:43 [PATCH v3 00/20] crypto: arm64 - play nice with CONFIG_PREEMPT Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 01/20] crypto: testmgr - add a new test case for CRC-T10DIF Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 02/20] crypto: arm64/aes-ce-ccm - move kernel mode neon en/disable into loop Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 03/20] crypto: arm64/aes-blk " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 04/20] crypto: arm64/aes-bs " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 05/20] crypto: arm64/chacha20 " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 06/20] crypto: arm64/aes-blk - remove configurable interleave Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 07/20] crypto: arm64/aes-blk - add 4 way interleave to CBC encrypt path Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 08/20] crypto: arm64/aes-blk - add 4 way interleave to CBC-MAC " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 09/20] crypto: arm64/sha256-neon - play nice with CONFIG_PREEMPT kernels Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 10/20] arm64: assembler: add utility macros to push/pop stack frames Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-07 14:11 ` Dave Martin 2017-12-07 14:11 ` Dave Martin 2017-12-07 14:21 ` Ard Biesheuvel 2017-12-07 14:21 ` Ard Biesheuvel 2017-12-07 14:53 ` Dave Martin 2017-12-07 14:53 ` Dave Martin 2017-12-07 14:58 ` Ard Biesheuvel 2017-12-07 14:58 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 11/20] arm64: assembler: add macros to conditionally yield the NEON under PREEMPT Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-07 14:39 ` Dave Martin [this message] 2017-12-07 14:39 ` Dave Martin 2017-12-07 14:50 ` Ard Biesheuvel 2017-12-07 14:50 ` Ard Biesheuvel 2017-12-07 15:47 ` Ard Biesheuvel 2017-12-07 15:47 ` Ard Biesheuvel 2017-12-07 15:51 ` Ard Biesheuvel 2017-12-07 15:51 ` Ard Biesheuvel 2017-12-07 16:15 ` Dave Martin 2017-12-07 16:15 ` Dave Martin 2017-12-07 16:11 ` Dave Martin 2017-12-07 16:11 ` Dave Martin 2017-12-06 19:43 ` [PATCH v3 12/20] crypto: arm64/sha1-ce - yield NEON after every block of input Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 13/20] crypto: arm64/sha2-ce " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 14/20] crypto: arm64/aes-ccm " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 15/20] crypto: arm64/aes-blk " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 16/20] crypto: arm64/aes-bs " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 17/20] crypto: arm64/aes-ghash " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 18/20] crypto: arm64/crc32-ce " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 19/20] crypto: arm64/crct10dif-ce " Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel 2017-12-06 19:43 ` [PATCH v3 20/20] DO NOT MERGE Ard Biesheuvel 2017-12-06 19:43 ` Ard Biesheuvel
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