On 2016/3/16 22:10, Bjorn Helgaas wrote:

On Wed, Mar 16, 2016 at 06:51:56PM +0800, Yongji Xie wrote:

quoted

Ping.

This is mainly VFIO stuff, and Alex had some security concerns, so I'm
not going to spend much time looking at this until he's satisfied.

When I do, I'll be looking hard at the resource_alignment kernel
parameter.  I'm opposed to kernel parameters in general because
they're very difficult for users to use correctly, and they lead to
kernel code paths that are rarely tested and hard to maintain.  So
I'll be looking for an excuse to reject changes in that area.

The changelog for 2/7 says it "replaces IORESOURCE_STARTALIGN with
IORESOURCE_WINDOW."  But even a glance at the patch itself shows that
IORESOURCE_WINDOW is *added* to some places, and it doesn't *replace*
IORESOURCE_STARTALIGN.

There is a problem with my statement. I mean we can use
IORESOURCE_WINDOW to identify bridge resources instead of
IORESOURCE_STARTALIGN here.

The changelog for 4/7 says:

   This is because vfio will not allow to passthrough one BAR's mmio
   page which may be shared with other BARs.  To solve this performance
   issue ...

with no mention at all of the actual *reason* vfio doesn't allow that
passthrough.  If I understand correctly, that reason has to do with
security, so your justification must be much stronger than "solving a
performance issue."

OK. I will try to make my justification become stronger.

Thanks,
Yongji Xie