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 13:28:20 -0800 |
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On 01/23/2017 01:16 PM, Yu-cheng Yu wrote: > On Mon, Jan 23, 2017 at 01:10:20PM -0800, Dave Hansen wrote: >> 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? > > The fix I am proposing is... > > state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | > xfeatures_mask;
Ahh, that makes sense. That does indeed look like a bug in fpstate_init().
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