This is a note to let you know that I've just added the patch titled
arm64: fpsimd: Bring cond_yield asm macro in line with new rules
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-fpsimd-bring-cond_yield-asm-macro-in-line-with.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 274bf11e1a161190262a73d1377bdc75fcc6e76b
Author: Ard Biesheuvel <ardb@xxxxxxxxxx>
Date: Thu Jan 11 12:24:48 2024 +0100
arm64: fpsimd: Bring cond_yield asm macro in line with new rules
[ Upstream commit 3931261ecf46151a5e779c96fb3da00677b6dc37 ]
We no longer disable softirqs or preemption when doing kernel mode SIMD,
and so for fully preemptible kernels, there is no longer a need to do any
explicit yielding (and for non-preemptible kernels, yielding is not
needed either).
That leaves voluntary preemption, where only explicit yield calls may
result in a reschedule. To retain the existing behavior for such a
configuration, we should take the new situation into account, where the
preempt count will be zero rather than one, and yielding to pending
softirqs is unnecessary.
Fixes: aefbab8e77eb ("arm64: fpsimd: Preserve/restore kernel mode NEON at context switch")
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240111112447.577640-2-ardb+git@xxxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 376a980f2bad0..5bcf021c372cc 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -760,32 +760,25 @@ alternative_endif
.endm
/*
- * Check whether preempt/bh-disabled asm code should yield as soon as
- * it is able. This is the case if we are currently running in task
- * context, and either a softirq is pending, or the TIF_NEED_RESCHED
- * flag is set and re-enabling preemption a single time would result in
- * a preempt count of zero. (Note that the TIF_NEED_RESCHED flag is
- * stored negated in the top word of the thread_info::preempt_count
+ * Check whether asm code should yield as soon as it is able. This is
+ * the case if we are currently running in task context, and the
+ * TIF_NEED_RESCHED flag is set. (Note that the TIF_NEED_RESCHED flag
+ * is stored negated in the top word of the thread_info::preempt_count
* field)
*/
- .macro cond_yield, lbl:req, tmp:req, tmp2:req
+ .macro cond_yield, lbl:req, tmp:req, tmp2
+#ifdef CONFIG_PREEMPT_VOLUNTARY
get_current_task \tmp
ldr \tmp, [\tmp, #TSK_TI_PREEMPT]
/*
* If we are serving a softirq, there is no point in yielding: the
* softirq will not be preempted no matter what we do, so we should
- * run to completion as quickly as we can.
+ * run to completion as quickly as we can. The preempt_count field will
+ * have BIT(SOFTIRQ_SHIFT) set in this case, so the zero check will
+ * catch this case too.
*/
- tbnz \tmp, #SOFTIRQ_SHIFT, .Lnoyield_\@
-#ifdef CONFIG_PREEMPTION
- sub \tmp, \tmp, #PREEMPT_DISABLE_OFFSET
cbz \tmp, \lbl
#endif
- adr_l \tmp, irq_stat + IRQ_CPUSTAT_SOFTIRQ_PENDING
- get_this_cpu_offset \tmp2
- ldr w\tmp, [\tmp, \tmp2]
- cbnz w\tmp, \lbl // yield on pending softirq in task context
-.Lnoyield_\@:
.endm
/*
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 5ff1942b04fcf..5a7dbbe0ce639 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -117,8 +117,6 @@ int main(void)
DEFINE(DMA_FROM_DEVICE, DMA_FROM_DEVICE);
BLANK();
DEFINE(PREEMPT_DISABLE_OFFSET, PREEMPT_DISABLE_OFFSET);
- DEFINE(SOFTIRQ_SHIFT, SOFTIRQ_SHIFT);
- DEFINE(IRQ_CPUSTAT_SOFTIRQ_PENDING, offsetof(irq_cpustat_t, __softirq_pending));
BLANK();
DEFINE(CPU_BOOT_TASK, offsetof(struct secondary_data, task));
BLANK();
