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

On Fri, 27 Nov 2020 11:39:50 +0100
David Hildenbrand <> wrote:

> On 20.11.20 16:13, Cornelia Huck wrote:
> > On Mon, 16 Nov 2020 20:16:29 +0100
> > David Hildenbrand <> 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 <>
> >> Cc: Marek Kedzierski <>
> >> Cc: Michael S. Tsirkin <>
> >> Cc: Cornelia Huck <>
> >> Signed-off-by: David Hildenbrand <>
> >> ---
> >>  virtio-mem.tex | 9 +++++++--
> >>  1 file changed, 7 insertions(+), 2 deletions(-)  
> > 
> > Looks reasonable to me.
> > 
> > Acked-by: Cornelia Huck <>  
> 
> Thanks!
> 
> I assume I'll need a github issue etc. to get this in, right?
> 

Yes; just open the issue, point to this patch in the archives, and
reply with the issue here.

(I don't think this is trivial enough to push without voting.)