Re: [PATCH v3 13/18] cxl: sysfs support for guests

[Ian Munsie <imunsie@au1.ibm.com>]

Excerpts from Frederic Barrat's message of 2016-02-10 02:21:19 +1100:
> 
> Le 08/02/2016 04:02, Stewart Smith a écrit :
> > Frederic Barrat <fbarrat@linux.vnet.ibm.com> writes:
> >> --- a/Documentation/ABI/testing/sysfs-class-cxl
> >> +++ b/Documentation/ABI/testing/sysfs-class-cxl
> >> @@ -183,7 +183,7 @@ Description:    read only
> >>                   Identifies the revision level of the PSL.
> >>   Users:        https://github.com/ibm-capi/libcxl
> >>
> >> -What:           /sys/class/cxl/<card>/base_image
> >> +What:           /sys/class/cxl/<card>/base_image (not in a guest)
> >
> > Is this going to be the case for KVM guest as well as PowerVM guest?
> 
> 
> That's too early to say.
> The entries we've removed are because the information is filtered by 
> pHyp and not available to the OS. Some of it because nobody thought it 
> would be useful, some of it because it's not meant to be seen by the OS. 
> For KVM, if the card can be shared between guests, I would expect the 
> same kind of restrictions.

The OS doesn't particularly care about this - the only people who might
even possibly need to know will be whoever is trying to flash their PSL
image, and probably not even then.

On KVM we are thinking that it will have to be root on the hypervisor
responsible for flashing the PSL image (there isn't much other option
unless we want to go into signed images and whatnot, but even if we do
I'm 100% committed to making that a userspace problem to solve and not
trying to do anything fancy in the kernel), so we won't really need it,
but I also don't see any harm in exposing it to guests.

Cheers,
-Ian