On Thu, 2020-05-07 at 20:22 +0200, Thomas Gleixner wrote:
> Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> writes:
> > @@ -983,6 +983,7 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
> > {
> > unsigned int offset, size;
> > struct xstate_header header;
> > + int last_off;
> > int i;
> >
> > /*
> > @@ -1006,7 +1007,17 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
> >
> > __copy_xstate_to_kernel(kbuf, &header, offset, size, size_total);
> >
> > + last_off = 0;
> > +
> > for (i = 0; i < XFEATURE_MAX; i++) {
> > + /*
> > + * Clear uninitialized area before XSAVE header.
> > + */
> > + if (i == FIRST_EXTENDED_XFEATURE) {
> > + memset(kbuf + last_off, 0, XSAVE_HDR_OFFSET - last_off);
> > + last_off = XSAVE_HDR_OFFSET + XSAVE_HDR_SIZE;
> > + }
> > +
> > /*
> > * Copy only in-use xstates:
> > */
> > @@ -1020,11 +1031,16 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
> > if (offset + size > size_total)
> > break;
> >
> > + memset(kbuf + last_off, 0, offset - last_off);
> > + last_off = offset + size;
> > +
> > __copy_xstate_to_kernel(kbuf, src, offset, size, size_total);
> > }
> >
> > }
> >
> > + memset(kbuf + last_off, 0, size_total - last_off);
>
> Why doing all this partial zeroing? There is absolutely no point.
>
> Either the caller clears the buffer or this function clears it right at
> the beginning with:
>
> memset(kbuf, 0, min(size_total, XSAVE_MAX_SIZE));
I was concerned that the XSAVES buffer can be large, but this is not in a
performance-critical path. Yes, clear it in the beginning is simpler.
Yu-cheng
