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ARM: vfp: Provide vfp_lock() for VFP locking.

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BugLink: https://bugs.launchpad.net/bugs/2060704

kernel_neon_begin() uses local_bh_disable() to ensure exclusive access
to the VFP unit. This is broken on PREEMPT_RT because a BH disabled
section remains preemptible on PREEMPT_RT.

Introduce vfp_lock() which uses local_bh_disable() and preempt_disable()
on PREEMPT_RT. Since softirqs are processed always in thread context,
disabling preemption is enough to ensure that the current context won't
get interrupted by something that is using the VFP. Use it in
kernel_neon_begin().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kevin Becker <kevin.becker@canonical.com>
This commit is contained in:
Sebastian Andrzej Siewior
2023-05-19 16:57:29 +02:00
committed by Kevin Becker
parent 8e81ad948b
commit ea8c2fd90b
1 changed files with 30 additions and 2 deletions
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arch/arm/vfp/vfpmodule.c
+30 -2
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@@ -55,6 +55,34 @@ extern unsigned int VFP_arch_feroceon __alias(VFP_arch);
*/
union vfp_state *vfp_current_hw_state[NR_CPUS];
/*
* Claim ownership of the VFP unit.
*
* The caller may change VFP registers until vfp_unlock() is called.
*
* local_bh_disable() is used to disable preemption and to disable VFP
* processing in softirq context. On PREEMPT_RT kernels local_bh_disable() is
* not sufficient because it only serializes soft interrupt related sections
* via a local lock, but stays preemptible. Disabling preemption is the right
* choice here as bottom half processing is always in thread context on RT
* kernels so it implicitly prevents bottom half processing as well.
*/
static void vfp_lock(void)
{
if (!IS_ENABLED(CONFIG_PREEMPT_RT))
local_bh_disable();
else
preempt_disable();
}
static void vfp_unlock(void)
{
if (!IS_ENABLED(CONFIG_PREEMPT_RT))
local_bh_enable();
else
preempt_enable();
}
/*
* Is 'thread's most up to date state stored in this CPUs hardware?
* Must be called from non-preemptible context.
@@ -837,7 +865,7 @@ void kernel_neon_begin(void)
unsigned int cpu;
u32 fpexc;
local_bh_disable();
vfp_lock();
/*
* Kernel mode NEON is only allowed outside of hardirq context with
@@ -868,7 +896,7 @@ void kernel_neon_end(void)
{
/* Disable the NEON/VFP unit. */
fmxr(FPEXC, fmrx(FPEXC) & ~FPEXC_EN);
local_bh_enable();
vfp_unlock();
}
EXPORT_SYMBOL(kernel_neon_end);