x86/fpu: Fix stale comments about lazy FPU logic (7f1487c5) · Commits · 戴 / test

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

+3 −6

Original line number	Diff line number	Diff line
		@@ -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);

Admin message