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SubjectRe: [PATCH 08/11] x86/fpu: Always store the registers in copy_fpstate_to_sigframe()
On 2018-10-12 11:15:51 [-0700], Dave Hansen wrote:
> > @@ -172,27 +155,20 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
> > sizeof(struct user_i387_ia32_struct), NULL,
> > (struct _fpstate_32 __user *) buf) ? -1 : 1;
> >
> > - if (fpu->initialized || using_compacted_format()) {
> > - /* Save the live register state to the user directly. */
> > - if (copy_fpregs_to_sigframe(buf_fx))
> > - return -1;
> > - /* Update the thread's fxstate to save the fsave header. */
> > - if (ia32_fxstate)
> > - copy_fxregs_to_kernel(fpu);
> > + /* Update the thread's fxstate to save the fsave header. */
> > + if (ia32_fxstate) {
> > + copy_fxregs_to_kernel(fpu);
> > } else {
> > - /*
> > - * It is a *bug* if kernel uses compacted-format for xsave
> > - * area and we copy it out directly to a signal frame. It
> > - * should have been handled above by saving the registers
> > - * directly.
> > - */
> > - if (boot_cpu_has(X86_FEATURE_XSAVES)) {
> > - WARN_ONCE(1, "x86/fpu: saving compacted-format xsave area to a signal frame!\n");
> > - return -1;
> > - }
> > + copy_fpregs_to_fpstate(fpu);
> > + fpregs_deactivate(fpu);
> > + }
>
> Could you add a high-level comment for this if{}else{} block that says
> something like:
>
> /* Save the registers to the fpstate. */
>
> I also think it's worthwhile to explain the asymmetry between the
> ia32_fxstate case and the other branch. Why don't we
> fpregs_deactivate() in the ia32_fxstate path, for instance?

Since the ->initialized is gone, the whole hunk here looks differently
and probably easier to understand.

> > + if (using_compacted_format()) {
> > + copy_xstate_to_user(buf_fx, xsave, 0, size);
> > + } else {
> > fpstate_sanitize_xstate(fpu);
> > - if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
> > + size = fpu_user_xstate_size;
> > + if (__copy_to_user(buf_fx, xsave, size))
> > return -1;
> > }

dropped this.

> This seems unnecessary. Why are you updating 'size' like this?

Sebastian

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