Re: Enabling RO on a VF

[Jason Gunthorpe]

On Fri, Oct 01, 2021 at 11:59:15AM +0000, Haakon Bugge wrote:
> 
> 
> > On 1 Oct 2021, at 13:54, Jason Gunthorpe <jgg@xxxxxxxx> wrote:
> > 
> > On Fri, Oct 01, 2021 at 11:05:15AM +0000, Haakon Bugge wrote:
> >> Hey,
> >> 
> >> 
> >> Commit 1477d44ce47d ("RDMA/mlx5: Enable Relaxed Ordering by default
> >> for kernel ULPs") uses pcie_relaxed_ordering_enabled() to check if
> >> RO can be enabled. This function checks if the Enable Relaxed
> >> Ordering bit in the Device Control register is set. However, on a
> >> VF, this bit is RsvdP (Reserved for future RW
> >> implementations. Register bits are read-only and must return zero
> >> when read. Software must preserve the value read for writes to
> >> bits.).
> >> 
> >> Hence, AFAICT, RO will not be enabled when using a VF.
> >> 
> >> How can that be fixed?
> > 
> > When qemu takes a VF and turns it into a PF in a VM it must emulate
> > the RO bit and return one
> 
> I have a pass-through VF:
> 
> # lspci -s ff:00.0 -vvv
> ff:00.0 Ethernet controller: Mellanox Technologies MT28800 Family [ConnectX-5 Ex Virtual Function]
> []
> 		DevCtl:	Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
> 			RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop- FLReset-

Like I said, it is a problem in the qemu area..

Jason