From: Ard Biesheuvel
mainline inclusion
from mainline-v5.12-rc1
commit d13c613f136c
category: bugfix
issue: #I3ZXZF
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
-----------------------------------------------
Add a macro cond_yield that branches to a specified label when called if
the TIF_NEED_RESCHED flag is set and decreasing the preempt count would
make the task preemptible again, resulting in a schedule to occur. This
can be used by kernel mode SIMD code that keeps a lot of state in SIMD
registers, which would make chunking the input in order to perform the
cond_resched() check from C code disproportionately costly.
Signed-off-by: Ard Biesheuvel
Link: https://lore.kernel.org/r/20210203113626.220151-2-ardb@kernel.org
Signed-off-by: Will Deacon
Signed-off-by: Wei Li
Reviewed-by: Jason Yan
Reviewed-by: Hanjun Guo
Signed-off-by: Chen Jun
Signed-off-by: Yu Changchun
---
arch/arm64/include/asm/assembler.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index ddbe6bf00e33..f1838bd93a40 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -745,6 +745,22 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
.Lyield_out_\@ :
.endm
+ /*
+ * Check whether preempt-disabled code should yield as soon as it
+ * is able. This is the case if re-enabling preemption a single
+ * time results in a preempt count of zero, and the TIF_NEED_RESCHED
+ * flag is set. (Note that the latter is stored negated in the
+ * top word of the thread_info::preempt_count field)
+ */
+ .macro cond_yield, lbl:req, tmp:req
+#ifdef CONFIG_PREEMPTION
+ get_current_task \tmp
+ ldr \tmp, [\tmp, #TSK_TI_PREEMPT]
+ sub \tmp, \tmp, #PREEMPT_DISABLE_OFFSET
+ cbz \tmp, \lbl
+#endif
+ .endm
+
/*
* This macro emits a program property note section identifying
* architecture features which require special handling, mainly for
--
2.22.0
