Re: [PATCH] memory: Skip dirty tracking for un-migratable memory regions

[Cornelia Huck]

On Mon, 16 Nov 2020 21:22:10 +0800
Zenghui Yu <yuzenghui@huawei.com> wrote:

> It makes no sense to track dirty pages for those un-migratable memory
> regions (e.g., Memory BAR region of the VFIO PCI device) and doing so
> will potentially lead to some unpleasant issues during migration [1].
> 
> Skip dirty tracking for those regions by evaluating if the region is
> migratable before setting dirty_log_mask (DIRTY_MEMORY_MIGRATION).
> 
> [1] https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg03757.html
> 
> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
>  softmmu/memory.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 71951fe4dc..aa393f1bb0 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -1806,7 +1806,10 @@ bool memory_region_is_ram_device(MemoryRegion *mr)
>  uint8_t memory_region_get_dirty_log_mask(MemoryRegion *mr)
>  {
>      uint8_t mask = mr->dirty_log_mask;
> -    if (global_dirty_log && (mr->ram_block || memory_region_is_iommu(mr))) {
> +    RAMBlock *rb = mr->ram_block;
> +
> +    if (global_dirty_log && ((rb && qemu_ram_is_migratable(rb)) ||
> +                             memory_region_is_iommu(mr))) {
>          mask |= (1 << DIRTY_MEMORY_MIGRATION);
>      }
>      return mask;

Looks reasonable.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>