Messages in this thread | | | Subject | Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly | From | Dave Hansen <> | Date | Mon, 2 May 2016 10:33:10 -0700 |
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On 05/02/2016 10:19 AM, Yu-cheng Yu wrote: > 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; > }
I don't think that changes anything. We still have a check in there that has no purpose. You've changed the ordering so that the specific example that I pointed out no longer triggers it. But, the underlying issue remains.
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