[virtio-comment] Re: [PATCH v1] virtio-mem: minor clarification regarding read-access to unplugged blocks

[Cornelia Huck <cohuck@redhat.com>]

On Mon, 16 Nov 2020 20:16:29 +0100
David Hildenbrand <david@redhat.com> wrote:

> Let's clarify that we don't expect all DMA to work with unplugged blocks.
> We really only give guarantees when reading from unplugged memory blocks
> via the CPU, e.g., as done by Linux when creating a system dump via
> kdump: the new kernel will copy the content of the old (crashed) kernel
> via the CPU to user space, from where it will find its final destination
> inside the dump file. Note that dumping via makedumpfile under Linux will
> avoid reading unplugged blocks completely.
> 
> This is a preparation for device passthrough to VMs, whereby such
> dedicated devices might not be able to read from unplugged memory blocks.
> 
> Let's document that this scenario is possible, and why this handling is
> in place at all.
> 
> Cc: teawater <teawaterz@linux.alibaba.com>
> Cc: Marek Kedzierski <mkedzier@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  virtio-mem.tex | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

Looks reasonable to me.

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


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