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

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 0/2] VFIO: Make 8-byte accesses atomic
Date: Fri, 21 Apr 2017 08:51:42 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 04/21/2017 03:06 AM, Paolo Bonzini wrote:

On 20/04/2017 18:03, Alex Williamson wrote:
On Thu, 20 Apr 2017 00:19:23 -0700
Richard Henderson <address@hidden> 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,
I agree, the patches looks fine as is.

Sorry, I misread the first patch, thinking that indicating hw support for 8 byte required implementation of 8 byte.


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