Re: [PATCH RFC 4/9] KVM: Create the KVMSlot dirty bitmap on flag changes

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> Previously we have two places that will create the per KVMSlot dirty
> bitmap:
> 
>   1. When a newly created KVMSlot has dirty logging enabled,
>   2. When the first log_sync() happens for a memory slot.
> 
> The 2nd case is lazy-init, while the 1st case is not (which is a fix
> of what the 2nd case missed).
> 
> To do explicit initialization of dirty bitmaps, what we're missing is
> to create the dirty bitmap when the slot changed from not-dirty-track
> to dirty-track.  Do that in kvm_slot_update_flags().
> 
> With that, we can safely remove the 2nd lazy-init.
> 
> This change will be needed for kvm dirty ring because kvm dirty ring
> does not use the log_sync() interface at all.
> 
> Since at it, move all the pre-checks into kvm_slot_init_dirty_bitmap().

'While at it' or just Also

> Signed-off-by: Peter Xu <peterx@redhat.com>


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  accel/kvm/kvm-all.c | 23 +++++++++--------------
>  1 file changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 4be3cd2352..bb635c775f 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -162,6 +162,8 @@ static NotifierList kvm_irqchip_change_notifiers =
>  #define kvm_slots_lock(kml)      qemu_mutex_lock(&(kml)->slots_lock)
>  #define kvm_slots_unlock(kml)    qemu_mutex_unlock(&(kml)->slots_lock)
>  
> +static void kvm_slot_init_dirty_bitmap(KVMSlot *mem);
> +
>  int kvm_get_max_memslots(void)
>  {
>      KVMState *s = KVM_STATE(current_accel());
> @@ -442,6 +444,7 @@ static int kvm_slot_update_flags(KVMMemoryListener *kml, KVMSlot *mem,
>          return 0;
>      }
>  
> +    kvm_slot_init_dirty_bitmap(mem);
>      return kvm_set_user_memory_region(kml, mem, false);
>  }
>  
> @@ -526,8 +529,12 @@ static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
>  #define ALIGN(x, y)  (((x)+(y)-1) & ~((y)-1))
>  
>  /* Allocate the dirty bitmap for a slot  */
> -static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem)
> +static void kvm_slot_init_dirty_bitmap(KVMSlot *mem)
>  {
> +    if (!(mem->flags & KVM_MEM_LOG_DIRTY_PAGES) || mem->dirty_bmap) {
> +        return;
> +    }
> +
>      /*
>       * XXX bad kernel interface alert
>       * For dirty bitmap, kernel allocates array of size aligned to
> @@ -578,11 +585,6 @@ static int kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
>              goto out;
>          }
>  
> -        if (!mem->dirty_bmap) {
> -            /* Allocate on the first log_sync, once and for all */
> -            kvm_memslot_init_dirty_bitmap(mem);
> -        }
> -
>          d.dirty_bitmap = mem->dirty_bmap;
>          d.slot = mem->slot | (kml->as_id << 16);
>          if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
> @@ -1079,14 +1081,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
>          mem->start_addr = start_addr;
>          mem->ram = ram;
>          mem->flags = kvm_mem_flags(mr);
> -
> -        if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
> -            /*
> -             * Reallocate the bmap; it means it doesn't disappear in
> -             * middle of a migrate.
> -             */
> -            kvm_memslot_init_dirty_bitmap(mem);
> -        }
> +        kvm_slot_init_dirty_bitmap(mem);
>          err = kvm_set_user_memory_region(kml, mem, true);
>          if (err) {
>              fprintf(stderr, "%s: error registering slot: %s\n", __func__,
> -- 
> 2.24.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK