Messages in this thread Patch in this message | | | From | Ingo Molnar <> | Subject | [PATCH 053/208] x86/fpu: Document fpu__unlazy_stopped() | Date | Tue, 5 May 2015 18:24:33 +0200 |
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Explain its usage and also document a TODO item.
Reviewed-by: Borislav Petkov <bp@alien8.de> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/kernel/fpu/core.c | 25 +++++++++++++++++++++---- 1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index b8e3dbbcdc16..0235df54cd48 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -284,10 +284,27 @@ int fpstate_alloc_init(struct task_struct *curr) EXPORT_SYMBOL_GPL(fpstate_alloc_init); /* - * The _current_ task is using the FPU for the first time - * so initialize it and set the mxcsr to its default - * value at reset if we support XMM instructions and then - * remember the current task has used the FPU. + * This function is called before we modify a stopped child's + * FPU state context. + * + * If the child has not used the FPU before then initialize its + * FPU context. + * + * If the child has used the FPU before then unlazy it. + * + * [ After this function call, after the context is modified and + * the child task is 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 + * state pending on its former CPU could be restored, losing + * the modifications. ] + * + * This function is also called before we read a stopped child's + * FPU state - to make sure it's modified. + * + * TODO: A future optimization would be to skip the unlazying in + * the read-only case, it's not strictly necessary for + * read-only access to the context. */ static int fpu__unlazy_stopped(struct task_struct *child) { -- 2.1.0
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