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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 18 Oct 2018 18:34:11 +0200
Subject: [PATCH 08/27] x86/fpu: Remove user_fpu_begin()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.10-rt7.tar.xz
user_fpu_begin() sets fpu_fpregs_owner_ctx to task's fpu struct. This is
always the case since there is no lazy FPU anymore.
fpu_fpregs_owner_ctx is used during context switch to decide if it needs
to load the saved registers or if the currently loaded registers are
valid. It could be skipped during
taskA -> kernel thread -> taskA
because the switch to kernel thread would not alter the CPU's FPU state.
Since this field is always updated during context switch and never
invalidated, setting it manually (in user context) makes no difference.
A kernel thread with kernel_fpu_begin() block could set
fpu_fpregs_owner_ctx to NULL but a kernel thread does not use
user_fpu_begin().
This is a leftover from the lazy-FPU time.
Remove user_fpu_begin(), it does not change fpu_fpregs_owner_ctx's
content.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/fpu/internal.h | 17 -----------------
arch/x86/kernel/fpu/core.c | 4 +---
arch/x86/kernel/fpu/signal.c | 1 -
3 files changed, 1 insertion(+), 21 deletions(-)
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -564,23 +564,6 @@ static inline void switch_fpu_finish(str
}
/*
- * Needs to be preemption-safe.
- *
- * NOTE! user_fpu_begin() must be used only immediately before restoring
- * the save state. It does not do any saving/restoring on its own. In
- * lazy FPU mode, it is just an optimization to avoid a #NM exception,
- * the task can lose the FPU right after preempt_enable().
- */
-static inline void user_fpu_begin(void)
-{
- struct fpu *fpu = ¤t->thread.fpu;
-
- preempt_disable();
- fpregs_activate(fpu);
- preempt_enable();
-}
-
-/*
* MXCSR and XCR definitions:
*/
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -335,10 +335,8 @@ void fpu__clear(struct fpu *fpu)
* Make sure fpstate is cleared and initialized.
*/
fpu__initialize(fpu);
- if (static_cpu_has(X86_FEATURE_FPU)) {
- user_fpu_begin();
+ if (static_cpu_has(X86_FEATURE_FPU))
copy_init_fpstate_to_fpregs();
- }
}
/*
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -322,7 +322,6 @@ static int __fpu__restore_sig(void __use
* For 64-bit frames and 32-bit fsave frames, restore the user
* state to the registers directly (with exceptions handled).
*/
- user_fpu_begin();
if (copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only)) {
fpu__clear(fpu);
return -1;
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