Re: [PATCH RESEND v4] nvme: introduce PMR support from NVMe 1.4 spec

[Klaus Birkelund Jensen]

On Mar 31 01:55, Keith Busch wrote:
> On Mon, Mar 30, 2020 at 09:46:56AM -0700, Andrzej Jakowski wrote:
> > This patch introduces support for PMR that has been defined as part of NVMe 
> > 1.4
> > spec. User can now specify a pmrdev option that should point to 
> > HostMemoryBackend.
> > pmrdev memory region will subsequently be exposed as PCI BAR 2 in emulated 
> > NVMe
> > device. Guest OS can perform mmio read and writes to the PMR region that 
> > will stay
> > persistent across system reboot.
> 
> Looks pretty good to me.
> 
> Reviewed-by: Keith Busch <address@hidden>
> 
> For a possible future extention, it could be interesting to select the
> BAR for PMR dynamically, so that you could have CMB and PMR enabled on
> the same device.
> 

I thought about the same thing, but this would require disabling MSI-X
right? Otherwise there is not enough room. AFAIU, the iomem takes up
BAR0 and BAR1, CMB (or PMR) uses BAR2 and BAR3 and MSI-X uses BAR4 or 5.