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Subject[tip:x86/fpu] x86/fpu: Fix stale comments about lazy FPU logic
Commit-ID:  7f1487c59b7c6dcb20155f4302985da2659a2997
Author: Ingo Molnar <>
AuthorDate: Sat, 23 Sep 2017 15:00:13 +0200
Committer: Ingo Molnar <>
CommitDate: Tue, 26 Sep 2017 09:43:43 +0200

x86/fpu: Fix stale comments about lazy FPU logic

We don't do any lazy restore anymore, what we have are two pieces of optimization:

- no-FPU tasks that don't save/restore the FPU context (kernel threads are such)

- cached FPU registers maintained via the fpu->last_cpu field. This means that
if an FPU task context switches to a non-FPU task then we can maintain the
FPU registers as an in-FPU copies (cache), and skip the restoration of them
once we switch back to the original FPU-using task.

Update all the comments that still referred to old 'lazy' and 'unlazy' concepts.

Cc: Andrew Morton <>
Cc: Andy Lutomirski <>
Cc: Borislav Petkov <>
Cc: Dave Hansen <>
Cc: Eric Biggers <>
Cc: Fenghua Yu <>
Cc: Linus Torvalds <>
Cc: Oleg Nesterov <>
Cc: Peter Zijlstra <>
Cc: Rik van Riel <>
Cc: Thomas Gleixner <>
Cc: Yu-cheng Yu <>
Signed-off-by: Ingo Molnar <>
arch/x86/kernel/fpu/core.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index c8d6032..77668d9 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -205,9 +205,6 @@ int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
* Save current FPU registers directly into the child
* FPU context, without any memory-to-memory copying.
- * In lazy mode, if the FPU context isn't loaded into
- * fpregs, CR0.TS will be set and do_device_not_available
- * will load the FPU context.
* We have to do all this with preemption disabled,
* mostly because of the FNSAVE case, because in that
@@ -285,13 +282,13 @@ void fpu__activate_fpstate_read(struct fpu *fpu)
* This function must be called before we write a task's fpstate.
- * If the task has used the FPU before then unlazy it.
+ * If the task has used the FPU before then invalidate any cached FPU registers.
* If the task has not used the FPU before then initialize its fpstate.
* After this function call, after registers in the fpstate are
* modified and the child task has woken up, the child task will
* restore the modified FPU state from the modified context. If we
- * didn't clear its lazy status here then the lazy in-registers
+ * didn't clear its cached status here then the cached in-registers
* state pending on its former CPU could be restored, corrupting
* the modifications.
@@ -304,7 +301,7 @@ void fpu__activate_fpstate_write(struct fpu *fpu)
WARN_ON_FPU(fpu == &current->thread.fpu);

if (fpu->initialized) {
- /* Invalidate any lazy state: */
+ /* Invalidate any cached state: */
} else {
 \ /
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