Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area

[Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>]

On Mon, Jan 23, 2017 at 07:36:20AM -0800, Dave Hansen wrote:
> The kernel xsave buffer should *ALWAYS* have the
> XCOMP_BV_COMPACTED_FORMAT bit set.  It should have been set before the
> copyin and it should be set when it's finished.
> 
> 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().

Also, in copy_init_fpstate_to_fpregs(), we do:

	copy_kernel_to_xregs(&init_fpstate.xsave, -1).

That (-1) could mean (0) because the parameters are declared as:

	copy_kernel_to_xregs(struct xregs_state *, u64)

Yu-cheng

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