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Re: [Qemu-devel] [PATCH v2 4/4] xen: Avoid VLA
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Qemu-devel] [PATCH v2 4/4] xen: Avoid VLA |
Date: |
Tue, 18 Jun 2019 13:35:23 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 |
On 6/18/19 1:23 PM, Anthony PERARD wrote:
> Avoid using a variable length array.
>
> We allocate the `dirty_bitmap' buffer only once when we start tracking
> for dirty bits.
>
Suggested-by: Paul Durrant <address@hidden>
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>
> 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);
> }
>
- [Qemu-devel] [PATCH v2 0/4] Fix build of Xen support + cleanup, Anthony PERARD, 2019/06/18
- [Qemu-devel] [PATCH v2 4/4] xen: Avoid VLA, Anthony PERARD, 2019/06/18
- [Qemu-devel] [PATCH v2 2/4] xen: Import other xen/io/*.h, Anthony PERARD, 2019/06/18
- [Qemu-devel] [PATCH v2 1/4] xen: Fix build with public headers, Anthony PERARD, 2019/06/18
- [Qemu-devel] [PATCH v2 3/4] xen: Drop includes of xen/hvm/params.h, Anthony PERARD, 2019/06/18
- Re: [Qemu-devel] [Xen-devel] [PATCH v2 0/4] Fix build of Xen support + cleanup, no-reply, 2019/06/18