Messages in this thread | | | Subject | Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area | From | Dave Hansen <> | Date | Mon, 23 Jan 2017 13:10:20 -0800 |
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On 01/23/2017 12:57 PM, Yu-cheng Yu wrote: > On Mon, Jan 23, 2017 at 09:23:06AM -0800, Dave Hansen wrote: >> On 01/23/2017 08:55 AM, Yu-cheng Yu wrote: >>>> The best fix here would be not to paper over the issue in the copy >>>> function but find where it got clobbered, or where some initialization >>>> code failed to set it. >>> >>> Someone else reported different issues from the same bug and a different >>> patch was just tested OK this morning. I think that adding xfeatures bits >>> to xcomp_bv should have been done in fpstate_init(). >> >> Right. So where did it get cleared out? > > It is not set until a task triggers XSAVES. We did not set it in fpstate_init() > because there is no valid data at the time.
The code is:
> void fpstate_init(union fpregs_state *state) > { > if (!static_cpu_has(X86_FEATURE_FPU)) { > fpstate_init_soft(&state->soft); > return; > } > > memset(state, 0, fpu_kernel_xstate_size); > > /* > * XRSTORS requires that this bit is set in xcomp_bv, or > * it will #GP. Make sure it is replaced after the memset(). > */ > if (static_cpu_has(X86_FEATURE_XSAVES)) > state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT;
That seems to set it unconditionally. What am I missing?
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