81 lines
2.5 KiB
Diff
81 lines
2.5 KiB
Diff
From 5f48127d0cf989d3c97d80ab73a022bd28097b8f Mon Sep 17 00:00:00 2001
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Fri, 19 May 2023 16:57:29 +0200
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Subject: [PATCH 177/196] ARM: vfp: Provide vfp_lock() for VFP locking.
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kernel_neon_begin() uses local_bh_disable() to ensure exclusive access
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to the VFP unit. This is broken on PREEMPT_RT because a BH disabled
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section remains preemptible on PREEMPT_RT.
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Introduce vfp_lock() which uses local_bh_disable() and preempt_disable()
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on PREEMPT_RT. Since softirqs are processed always in thread context,
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disabling preemption is enough to ensure that the current context won't
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get interrupted by something that is using the VFP. Use it in
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kernel_neon_begin().
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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arch/arm/vfp/vfpmodule.c | 32 ++++++++++++++++++++++++++++++--
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1 file changed, 30 insertions(+), 2 deletions(-)
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diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
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index 7e8773a2d99d..8d321cdb7ac5 100644
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--- a/arch/arm/vfp/vfpmodule.c
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+++ b/arch/arm/vfp/vfpmodule.c
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@@ -55,6 +55,34 @@ extern unsigned int VFP_arch_feroceon __alias(VFP_arch);
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*/
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union vfp_state *vfp_current_hw_state[NR_CPUS];
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+/*
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+ * Claim ownership of the VFP unit.
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+ *
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+ * The caller may change VFP registers until vfp_unlock() is called.
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+ *
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+ * local_bh_disable() is used to disable preemption and to disable VFP
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+ * processing in softirq context. On PREEMPT_RT kernels local_bh_disable() is
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+ * not sufficient because it only serializes soft interrupt related sections
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+ * via a local lock, but stays preemptible. Disabling preemption is the right
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+ * choice here as bottom half processing is always in thread context on RT
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+ * kernels so it implicitly prevents bottom half processing as well.
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+ */
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+static void vfp_lock(void)
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+{
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+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
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+ local_bh_disable();
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+ else
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+ preempt_disable();
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+}
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+
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+static void vfp_unlock(void)
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+{
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+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
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+ local_bh_enable();
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+ else
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+ preempt_enable();
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+}
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+
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/*
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* Is 'thread's most up to date state stored in this CPUs hardware?
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* Must be called from non-preemptible context.
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@@ -819,7 +847,7 @@ void kernel_neon_begin(void)
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unsigned int cpu;
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u32 fpexc;
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- local_bh_disable();
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+ vfp_lock();
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/*
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* Kernel mode NEON is only allowed outside of hardirq context with
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@@ -850,7 +878,7 @@ void kernel_neon_end(void)
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{
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/* Disable the NEON/VFP unit. */
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fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
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- local_bh_enable();
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+ vfp_unlock();
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}
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EXPORT_SYMBOL(kernel_neon_end);
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--
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2.43.2
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