Re: [Qemu-devel] [RFC PATCH qemu] vfio-quirks: Pass the actual parent when deleting a memory region

[David Gibson]

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 <address@hidden>

Reviewed-by: David Gibson <address@hidden>

> ---
> 
> 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]);
>          }
>      }
>  }

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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