Messages in this thread | | | Date | Mon, 2 May 2016 10:19:36 -0700 | From | Yu-cheng Yu <> | Subject | Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly |
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On Mon, May 02, 2016 at 09:43:47AM -0700, Dave Hansen wrote: > > If (fpu.fpstate_active == 0), then the task does not use FPU; we don't > > want to save these registers, right? > > No. It's possible to have fpstate_active=0 while fpregs_active=1. Such > a task uses the FPU, but just hasn't done an XSAVE* to save the register > content to the fpstate buffer. > > Note, this is just theoretical, and does not happen in this particular > call path today.
What about...
static int may_copy_fpregs_to_sigframe(void) { if (fpregs_active()) return 1;
WARN_ONCE(!current->thread.fpu.fpstate_active, "direct FPU save with no math use\n");
if (boot_cpu_has(X86_FEATURE_XSAVES)) return 1;
return 0; }
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