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[Qemu-devel] [PATCH v2 4/4] xen: Avoid VLA
From: |
Anthony PERARD |
Subject: |
[Qemu-devel] [PATCH v2 4/4] xen: Avoid VLA |
Date: |
Tue, 18 Jun 2019 12:23:41 +0100 |
Avoid using a variable length array.
We allocate the `dirty_bitmap' buffer only once when we start tracking
for dirty bits.
Signed-off-by: Anthony PERARD <address@hidden>
---
Notes:
v2:
- Allocate the bitmap buffer only once when we start tracking dirty bits.
(instead of at every function call)
Was suggested by Peter here:
<address@hidden>
"should we try to stop using variable length arrays?"
hw/i386/xen/xen-hvm.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/hw/i386/xen/xen-hvm.c b/hw/i386/xen/xen-hvm.c
index ae3deb4ef3..469f1260a4 100644
--- a/hw/i386/xen/xen-hvm.c
+++ b/hw/i386/xen/xen-hvm.c
@@ -119,6 +119,8 @@ typedef struct XenIOState {
DeviceListener device_listener;
hwaddr free_phys_offset;
const XenPhysmap *log_for_dirtybit;
+ /* Buffer used by xen_sync_dirty_bitmap */
+ unsigned long *dirty_bitmap;
Notifier exit;
Notifier suspend;
@@ -464,6 +466,8 @@ static int xen_remove_from_physmap(XenIOState *state,
QLIST_REMOVE(physmap, list);
if (state->log_for_dirtybit == physmap) {
state->log_for_dirtybit = NULL;
+ g_free(state->dirty_bitmap);
+ state->dirty_bitmap = NULL;
}
g_free(physmap);
@@ -614,7 +618,7 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
{
hwaddr npages = size >> TARGET_PAGE_BITS;
const int width = sizeof(unsigned long) * 8;
- unsigned long bitmap[DIV_ROUND_UP(npages, width)];
+ size_t bitmap_size = DIV_ROUND_UP(npages, width);
int rc, i, j;
const XenPhysmap *physmap = NULL;
@@ -626,13 +630,14 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
if (state->log_for_dirtybit == NULL) {
state->log_for_dirtybit = physmap;
+ state->dirty_bitmap = g_new(unsigned long, bitmap_size);
} else if (state->log_for_dirtybit != physmap) {
/* Only one range for dirty bitmap can be tracked. */
return;
}
rc = xen_track_dirty_vram(xen_domid, start_addr >> TARGET_PAGE_BITS,
- npages, bitmap);
+ npages, state->dirty_bitmap);
if (rc < 0) {
#ifndef ENODATA
#define ENODATA ENOENT
@@ -646,8 +651,8 @@ static void xen_sync_dirty_bitmap(XenIOState *state,
return;
}
- for (i = 0; i < ARRAY_SIZE(bitmap); i++) {
- unsigned long map = bitmap[i];
+ for (i = 0; i < bitmap_size; i++) {
+ unsigned long map = state->dirty_bitmap[i];
while (map != 0) {
j = ctzl(map);
map &= ~(1ul << j);
@@ -677,6 +682,8 @@ static void xen_log_stop(MemoryListener *listener,
MemoryRegionSection *section,
if (old & ~new & (1 << DIRTY_MEMORY_VGA)) {
state->log_for_dirtybit = NULL;
+ g_free(state->dirty_bitmap);
+ state->dirty_bitmap = NULL;
/* Disable dirty bit tracking */
xen_track_dirty_vram(xen_domid, 0, 0, NULL);
}
--
Anthony PERARD