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X86 FPU updates:

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- Simplify the FPU protection for !RT kernels
 
  - Add the RT variant of FPU protections
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Merge tag 'x86-fpu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 FPU updates from Thomas Gleixner:

 - Simplify the FPU protection for !RT kernels

 - Add the RT variant of FPU protections

* tag 'x86-fpu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fpu: Make kernel FPU protection RT friendly
  x86/fpu: Simplify fpregs_[un]lock()
This commit is contained in:
Linus Torvalds 2020-12-14 18:47:38 -08:00
commit eb0ea74120
1 changed files with 19 additions and 4 deletions
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23
arch/x86/include/asm/fpu/api.h
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@ -29,17 +29,32 @@ extern void fpregs_mark_activate(void);
* A context switch will (and softirq might) save CPU's FPU registers to
* fpu->state and set TIF_NEED_FPU_LOAD leaving CPU's FPU registers in
* a random state.
*
* local_bh_disable() protects against both preemption and soft interrupts
* on !RT kernels.
*
* On 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.
*
* Disabling preemption also serializes against kernel_fpu_begin().
*/
static inline void fpregs_lock(void)
{
preempt_disable();
local_bh_disable();
if (!IS_ENABLED(CONFIG_PREEMPT_RT))
local_bh_disable();
else
preempt_disable();
}
static inline void fpregs_unlock(void)
{
local_bh_enable();
preempt_enable();
if (!IS_ENABLED(CONFIG_PREEMPT_RT))
local_bh_enable();
else
preempt_enable();
}
#ifdef CONFIG_X86_DEBUG_FPU