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

On 20.11.20 16:13, Cornelia Huck wrote:
> 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>


I assume I'll need a github issue etc. to get this in, right?


David / dhildenb

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