Re: [Qemu-devel] [PATCH 0/2] VFIO: Make 8-byte accesses atomic

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 20 Apr 2017 00:19:23 -0700
Richard Henderson <rth@twiddle.net> wrote:

> On 04/19/2017 12:44 PM, Jose Ricardo Ziviani wrote:
> > This patchset has two patches:
> > [1] 8-byte writes to non-mapped MMIO are broken into pairs of 4-byte writes, this patch makes such pairs atomic.
> >
> > [2] Enable 8-byte accesses in vfio_region_write and vfio_region_read.
> >
> > Patches based on master.
> >
> > Jose Ricardo Ziviani (2):
> >   vfio: Set MemoryRegionOps:max_access_size and min_access_size
> >   vfio: enable 8-byte reads/writes to vfio
> >
> >  hw/vfio/common.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >  
> 
> I think these patches need to be squashed to be bisectable.

No, I think it's fine.  The point of patch 1/2 is to indicate that the
hardware supports 8-byte accesses, which will still be broken into 2
4-byte accesses because we don't yet set the implemented width beyond
the default.  The important part is that the mutex will now group the 4
byte access pair together rather than letting them get re-ordered.
Patch 2/2 then implements native 8-byte access.  I appreciate them
being separate for this subtle nuance, but maybe I'm not seeing the
same issue as you.  Thanks,

Alex