Re: [PATCH v2 10/29] vfio/container: pass MemoryRegion to DMA operations

[John Levon <john.levon@nutanix.com>]

On Wed, May 21, 2025 at 09:43:11AM +0200, Cédric Le Goater wrote:

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> +Steven,
> 
> On 5/20/25 17:03, John Levon wrote:
> > Pass through the MemoryRegion to DMA operation handlers of vfio
> > containers. The vfio-user container will need this later, to translate
> > the vaddr into an offset for the dma map vfio-user message.
> > 
> > Originally-by: John Johnson <john.g.johnson@oracle.com>
> > Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> > Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> > Signed-off-by: John Levon <john.levon@nutanix.com>
> 
> 
> This change conflicts with :
> 
>   https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_qemu-2Ddevel_1747063973-2D124548-2D28-2Dgit-2Dsend-2Demail-2Dsteven.sistare-40oracle.com&d=DwICaQ&c=s883GpUCOChKOHiocYtGcg&r=v7SNLJqx7b9Vfc7ZO82Wg4nnZ8O5XkACFQ30bVKxotI&m=ZGgaPL84zJdxC-NJiZdGWRzh1WIXiIKzDUt8YcytF-NfxOT9I_gSOxNCph5DfyVM&s=V-_fptKbd0WpQ_JDJWze9TxsbOrvVfEm2EIPPH6HJ2k&e=
> 
> Steven,
> 
> Could we use this version instead for the "live update" series ?

I could use the ram block for the offset but the mrp is also used here:

  86     int fd = memory_region_get_fd(mrp);

which is

  2406 int memory_region_get_fd(MemoryRegion *mr)
  2407 {
  2408     RCU_READ_LOCK_GUARD();
  2409     while (mr->alias) {
  2410         mr = mr->alias;
  2411     }
  2412     return mr->ram_block->fd;
  2413 }

In the tests I've done, mr->alias is always NULL, but I don't know enough about
MR handling to be sure this will always be the case? Perhaps others can, in
which case I only need the ram block too.

regards
john