* Dave Hansen <dave.han...@linux.intel.com> wrote:
> On 11/16/2016 08:56 AM, Yu-cheng Yu wrote:
> > Robert O'Callahan reported that after an execve PTRACE_GETREGSET
> > NT_X86_XSTATE continues to return the pre-exec register values
> > until the exec'ed task modifies FPU state. The test code is at
> > https://bugzilla.redhat.com/attachment.cgi?id=1164286.
> >
> > What is happening is when eagerfpu is enabled, fpu__clear() did
> > not properly clear fpstate. Fix it by doing just that.
>
> Functionally, I think the patch is fine. just a few
> comment/documentation nits.
>
> I think fpu__clear()'s comments are a bit out of date. Could we make it
> clear that it is invalidating both fpregs *and* fpstate?
>
> I also think the
>
> /* FPU state will be reallocated lazily at the first use. */"
>
> comment was fairly valuable. Could we find some way to keep it?
>
> The new comment:
>
> > + /*
> > + * When eagerfpu is used, make sure fpstate is cleared and initialized.
> > + */
>
> also kinda implies that the if() block is only messing with fpstate.
> Could we make that more clear? Maybe by commenting the individual lines
> inside the if():
>
> > + if (use_eager_fpu()) {
> > + fpu__activate_curr(fpu);
> > + user_fpu_begin();
>
> instead of having it above? Maybe something like:
>
> if (use_eager_fpu()) {
> /* activate and load init fpstate into 'fpu' */
> fpu__activate_curr(fpu);
> /* re-activate fpregs: */
> user_fpu_begin();
> /* take new init fpstate and place in fpregs: */
> copy_init_fpstate_to_fpregs();
> }
I agree with these suggestions - but I'll apply the simple patch to x86/urgent
-
which can then be backported as far as necessary, and then resolve the conflict
with the v4.10 tip:x86/fpu branch, and on top of that we can fix these details,
ok?
In particular I don't like it how non-obvious the semantics are from the
function
names. I think we should try to improve the nomenclature instead of adding
comments to every line.
Thanks,
Ingo
