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-rw-r--r--arch/arm64/include/asm/assembler.h73
-rw-r--r--arch/arm64/kernel/asm-offsets.c3
2 files changed, 76 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index fe2ff3efe1f0..0bcc98dbba56 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -628,4 +628,77 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
.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 <label>
+ *
+ * where <label> is optional, and marks the point where execution will resume
+ * after a yield has been performed. If omitted, execution resumes right after
+ * the endif_yield_neon invocation. Note that the entire sequence, including
+ * the provided patchup code, will be omitted from the image if CONFIG_PREEMPT
+ * is not defined.
+ *
+ * As a convenience, in the case where no patchup code is required, the above
+ * sequence may be abbreviated to
+ *
+ * cond_yield_neon <label>
+ *
+ * Note that the patchup code does not support assembler directives that change
+ * the output section, any use of such directives is undefined.
+ *
+ * The yield itself consists of the following:
+ * - Check whether the preempt count is exactly 1, in which case disabling
+ * 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.
+ *
+ * This macro sequence may clobber all CPU state that is not guaranteed by the
+ * AAPCS to be preserved across an ordinary function call.
+ */
+
+ .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, #PREEMPT_DISABLE_OFFSET
+ csel x0, x0, xzr, eq
+ tbnz x0, #TIF_NEED_RESCHED, .Lyield_\@ // needs rescheduling?
+ /* fall through to endif_yield_neon */
+ .subsection 1
+.Lyield_\@ :
+#else
+ .section ".discard.cond_yield_neon", "ax"
+#endif
+ .endm
+
+ .macro do_cond_yield_neon
+ bl kernel_neon_end
+ bl kernel_neon_begin
+ .endm
+
+ .macro endif_yield_neon, lbl
+ .ifnb \lbl
+ b \lbl
+ .else
+ b .Lyield_out_\@
+ .endif
+ .previous
+.Lyield_out_\@ :
+ .endm
+
#endif /* __ASM_ASSEMBLER_H */
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 78e1b0a70aaf..5bdda651bd05 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -23,6 +23,7 @@
#include <linux/mm.h>
#include <linux/dma-mapping.h>
#include <linux/kvm_host.h>
+#include <linux/preempt.h>
#include <linux/suspend.h>
#include <asm/cpufeature.h>
#include <asm/fixmap.h>
@@ -93,6 +94,8 @@ int main(void)
DEFINE(DMA_TO_DEVICE, DMA_TO_DEVICE);
DEFINE(DMA_FROM_DEVICE, DMA_FROM_DEVICE);
BLANK();
+ DEFINE(PREEMPT_DISABLE_OFFSET, PREEMPT_DISABLE_OFFSET);
+ BLANK();
DEFINE(CLOCK_REALTIME, CLOCK_REALTIME);
DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC);
DEFINE(CLOCK_MONOTONIC_RAW, CLOCK_MONOTONIC_RAW);
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