Re: [PATCH RFC] virtio-mem: check against memhp_get_pluggable_range() which memory we can hotplug

[Anshuman Khandual]

On 1/11/21 6:11 PM, David Hildenbrand wrote:
> Right now, we only check against MAX_PHYSMEM_BITS - but turns out there
> are more restrictions of which memory we can actually hotplug, especially
> om arm64 or s390x once we support them: we might receive something like
> -E2BIG or -ERANGE from add_memory_driver_managed(), stopping device
> operation.
> 
> So, check right when initializing the device which memory we can add,
> warning the user. Try only adding actually pluggable ranges: in the worst
> case, no memory provided by our device is pluggable.
> 
> In the usual case, we expect all device memory to be pluggable, and in
> corner cases only some memory at the end of the device-managed memory
> region to not be pluggable.
> 
> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
> Cc: Jason Wang <jasowang@xxxxxxxxxx>
> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: catalin.marinas@xxxxxxx
> Cc: teawater <teawaterz@xxxxxxxxxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Pankaj Gupta <pankaj.gupta@xxxxxxxxxxxxxxx>
> Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Cc: hca@xxxxxxxxxxxxx
> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> 
> This is an example how virito-mem intends to use an interface like
> memhp_get_pluggable_range() once around. See:
> 
> "[PATCH V2 0/3] mm/hotplug: Pre-validate the address range with platform"
> https://lkml.kernel.org/r/1608218912-28932-1-git-send-email-anshuman.khandual@xxxxxxx
> 
> @Anshuman, feel free to pick up and carry this patch. I'll retest the final
> result / new versions of you series.

Makes sense, will carry this patch in the series.