Re: [Qemu-devel] [PATCH v4 1/6] vhost: Move log_dirty check

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 13 Dec 2017 18:08:02 +0000
"Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:

> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Move the log_dirty check into vhost_section.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  hw/virtio/trace-events |  3 +++
>  hw/virtio/vhost.c      | 20 +++++++++++++-------
>  2 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
> index 775461ae98..4a493bcd46 100644
> --- a/hw/virtio/trace-events
> +++ b/hw/virtio/trace-events
> @@ -1,5 +1,8 @@
>  # See docs/devel/tracing.txt for syntax documentation.
>  
> +# hw/virtio/vhost.c
> +vhost_section(const char *name, int r) "%s:%d"
> +
>  # hw/virtio/virtio.c
>  virtqueue_alloc_element(void *elem, size_t sz, unsigned in_num, unsigned out_num) "elem %p size %zd in_num %u out_num %u"
>  virtqueue_fill(void *vq, const void *elem, unsigned int len, unsigned int idx) "vq %p elem %p len %u idx %u"
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index e4290ce93d..e923219e63 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -27,6 +27,7 @@
>  #include "hw/virtio/virtio-access.h"
>  #include "migration/blocker.h"
>  #include "sysemu/dma.h"
> +#include "trace.h"
>  
>  /* enabled until disconnected backend stabilizes */
>  #define _VHOST_DEBUG 1
> @@ -567,18 +568,12 @@ static void vhost_set_memory(MemoryListener *listener,
>                                           memory_listener);
>      hwaddr start_addr = section->offset_within_address_space;
>      ram_addr_t size = int128_get64(section->size);
> -    bool log_dirty =
> -        memory_region_get_dirty_log_mask(section->mr) & ~(1 << DIRTY_MEMORY_MIGRATION);
>      int s = offsetof(struct vhost_memory, regions) +
>          (dev->mem->nregions + 1) * sizeof dev->mem->regions[0];
>      void *ram;
>  
>      dev->mem = g_realloc(dev->mem, s);
>  
> -    if (log_dirty) {
> -        add = false;
> -    }
> -
>      assert(size);
>  
>      /* Optimize no-change case. At least cirrus_vga does this a lot at this time. */
> @@ -611,8 +606,19 @@ static void vhost_set_memory(MemoryListener *listener,
>  
>  static bool vhost_section(MemoryRegionSection *section)
>  {
> -    return memory_region_is_ram(section->mr) &&
> +    bool result;
> +    bool log_dirty = memory_region_get_dirty_log_mask(section->mr) &
> +                     ~(1 << DIRTY_MEMORY_MIGRATION);
> +    result = memory_region_is_ram(section->mr) &&
>          !memory_region_is_rom(section->mr);
> +
> +    /* Vhost doesn't handle any block which is doing dirty-tracking other
> +     * than migration; this typically fires on VGA areas.
> +     */
> +    result &= !log_dirty;
before patch even if log_dirty, vhost_set_memory will still proceed
and may remove dirty section from memmap and set memory_changed = true

but with this patch it will just ignore such section,
I'm not sure it's right (it might be right with new approach add/nop
but then this patch should go after new code in place and old one
if gone).

> +
> +    trace_vhost_section(section->mr->name, result);
> +    return result;
>  }
>  
>  static void vhost_begin(MemoryListener *listener)