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Subject[tip:x86/fpu] x86/fpu: Fix stale comments about lazy FPU logic
Commit-ID:  7f1487c59b7c6dcb20155f4302985da2659a2997
Gitweb: http://git.kernel.org/tip/7f1487c59b7c6dcb20155f4302985da2659a2997
Author: Ingo Molnar <mingo@kernel.org>
AuthorDate: Sat, 23 Sep 2017 15:00:13 +0200
Committer: Ingo Molnar <mingo@kernel.org>
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 <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170923130016.21448-31-mingo@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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: */
__fpu_invalidate_fpregs_state(fpu);
} else {
fpstate_init(&fpu->state);
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