On Thu, 2020-05-07 at 20:22 +0200, Thomas Gleixner wrote:
Yu-cheng Yu yu-cheng.yu@intel.com 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