[RFC,qemu] vfio-quirks: Pass the actual parent when deleting a memory region

The usual way of using a quirk's MR is to add it as a subregion of a BAR
as this is what quirks are for. However there is less than standard user
of this - NVLink2-enabled NVIDIA GPU which exposes a GPU RAM and a ATSD
64K region outside of PCI MMIO window so these MRs get the system address
space root as a parent. So when the user unplugs such device, assert
occurs:

qemu-system-ppc64: /home/aik/p/qemu/memory.c:2391: memory_region_del_subregion: Assertion `subregion->container == mr' failed.

This passes the actual parent MR to memory_region_del_subregion() in
vfio_bar_quirk_exit.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---

This removes an extra sanity check that a quirk has a correct parent;
I am not sure if it is very useful.
I could use the "system" MR if quirk->mem[i].container==get_system_memory()
and quirk->mem[i].container otherwise to keep that assert working.

Also this does not help with the actual device removal much because of
the closed source driver nature - the associated service
(nvidia-persistenced, responsible for onlining GPU memory) crashes
the guest system but at least the user can reboot the guest after
the crash which is not as bad as assert.

---
 hw/vfio/pci-quirks.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

On Fri, Jul 05, 2019 at 01:25:01PM +1000, Alexey Kardashevskiy wrote:
> The usual way of using a quirk's MR is to add it as a subregion of a BAR
> as this is what quirks are for. However there is less than standard user
> of this - NVLink2-enabled NVIDIA GPU which exposes a GPU RAM and a ATSD
> 64K region outside of PCI MMIO window so these MRs get the system address
> space root as a parent. So when the user unplugs such device, assert
> occurs:
> 
> qemu-system-ppc64: /home/aik/p/qemu/memory.c:2391: memory_region_del_subregion: Assertion `subregion->container == mr' failed.
> 
> This passes the actual parent MR to memory_region_del_subregion() in
> vfio_bar_quirk_exit.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> 
> This removes an extra sanity check that a quirk has a correct parent;
> I am not sure if it is very useful.
> I could use the "system" MR if quirk->mem[i].container==get_system_memory()
> and quirk->mem[i].container otherwise to keep that assert working.
> 
> Also this does not help with the actual device removal much because of
> the closed source driver nature - the associated service
> (nvidia-persistenced, responsible for onlining GPU memory) crashes
> the guest system but at least the user can reboot the guest after
> the crash which is not as bad as assert.
> 
> ---
>  hw/vfio/pci-quirks.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/pci-quirks.c b/hw/vfio/pci-quirks.c
> index 27dddbc8fa3e..ef2e182c1d36 100644
> --- a/hw/vfio/pci-quirks.c
> +++ b/hw/vfio/pci-quirks.c
> @@ -1896,7 +1896,8 @@ void vfio_bar_quirk_exit(VFIOPCIDevice *vdev, int nr)
>          }
>  
>          for (i = 0; i < quirk->nr_mem; i++) {
> -            memory_region_del_subregion(bar->region.mem, &quirk->mem[i]);
> +            memory_region_del_subregion(quirk->mem[i].container,
> +                                        &quirk->mem[i]);
>          }
>      }
>  }

On Fri,  5 Jul 2019 13:25:01 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> The usual way of using a quirk's MR is to add it as a subregion of a BAR
> as this is what quirks are for. However there is less than standard user
> of this - NVLink2-enabled NVIDIA GPU which exposes a GPU RAM and a ATSD
> 64K region outside of PCI MMIO window so these MRs get the system address
> space root as a parent. So when the user unplugs such device, assert
> occurs:
> 
> qemu-system-ppc64: /home/aik/p/qemu/memory.c:2391: memory_region_del_subregion: Assertion `subregion->container == mr' failed.
> 
> This passes the actual parent MR to memory_region_del_subregion() in
> vfio_bar_quirk_exit.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> 
> This removes an extra sanity check that a quirk has a correct parent;
> I am not sure if it is very useful.
> I could use the "system" MR if quirk->mem[i].container==get_system_memory()
> and quirk->mem[i].container otherwise to keep that assert working.
> 
> Also this does not help with the actual device removal much because of
> the closed source driver nature - the associated service
> (nvidia-persistenced, responsible for onlining GPU memory) crashes
> the guest system but at least the user can reboot the guest after
> the crash which is not as bad as assert.
> 
> ---
>  hw/vfio/pci-quirks.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/pci-quirks.c b/hw/vfio/pci-quirks.c
> index 27dddbc8fa3e..ef2e182c1d36 100644
> --- a/hw/vfio/pci-quirks.c
> +++ b/hw/vfio/pci-quirks.c
> @@ -1896,7 +1896,8 @@ void vfio_bar_quirk_exit(VFIOPCIDevice *vdev, int nr)
>          }
>  
>          for (i = 0; i < quirk->nr_mem; i++) {
> -            memory_region_del_subregion(bar->region.mem, &quirk->mem[i]);
> +            memory_region_del_subregion(quirk->mem[i].container,
> +                                        &quirk->mem[i]);
>          }
>      }
>  }

NAK

struct MemoryRegion {
    Object parent_obj;

    /* All fields are private - violators will be prosecuted */
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    MemoryRegion *container;