Re: [Qemu-devel] [qemu PATCH v4 3/4] nvdimm, acpi: support NFIT platform capabilities

[Dan Williams]

On Tue, Jun 5, 2018 at 3:07 PM, Ross Zwisler
<address@hidden> wrote:
> On Tue, Jun 05, 2018 at 09:37:25PM +0300, Michael S. Tsirkin wrote:
>> On Tue, Jun 05, 2018 at 11:15:00AM -0700, Dan Williams wrote:
>> > On Tue, Jun 5, 2018 at 9:42 AM, Ross Zwisler
>> > <address@hidden> wrote:
>> > > On Tue, Jun 05, 2018 at 06:25:27PM +0300, Michael S. Tsirkin wrote:
>> > >> On Mon, May 21, 2018 at 10:32:02AM -0600, Ross Zwisler wrote:
>> > >> > Add a machine command line option to allow the user to control the 
>> > >> > Platform
>> > >> > Capabilities Structure in the virtualized NFIT.  This Platform 
>> > >> > Capabilities
>> > >> > Structure was added in ACPI 6.2 Errata A.
>> > >> >
>> > >> > Signed-off-by: Ross Zwisler <address@hidden>
>> > >>
>> > >> I tried playing with it and encoding the capabilities is
>> > >> quite awkward.
>> > >>
>> > >> Can we add bits for specific capabilities instead of nvdimm-cap?
>> > >>
>> > >> How about:
>> > >>
>> > >> "cpu-flush-on-power-loss-cap"
>> > >> "memory-flush-on-power-loss-cap"
>> > >> "byte-addressable-mirroring-cap"
>> > >
>> > > Hmmm...I don't like that as much because:
>> > >
>> > > a) It's very verbose.  Looking at my current qemu command line few other
>> > >    options require that many characters, and you'd commonly be defining 
>> > > more
>> > >    than one of these for a given VM.
>> > >
>> > > b) It means that the QEMU will need to be updated if/when new flags are 
>> > > added,
>> > >    because we'll have to have new options for each flag.  The current
>> > >    implementation is more future-proof because you can specify any flags
>> > >    value you want.
>> > >
>> > > However, if you feel strongly about this, I'll make the change.
>> >
>> > Straw-man: Could we do something similar with what we are doing in ndctl?
>> >
>> > enum ndctl_persistence_domain {
>> >         PERSISTENCE_NONE = 0,
>> >         PERSISTENCE_MEM_CTRL = 10,
>> >         PERSISTENCE_CPU_CACHE = 20,
>> >         PERSISTENCE_UNKNOWN = INT_MAX,
>> > };
>> >
>> > ...and have the command line take a number where "10" and "20" are
>> > supported today, but allows us to adapt to new persistence domains in
>> > the future.
>>
>> I'm fine with that except can we have symbolic names instead of numbers
>> on command line?
>>
>> --
>> MST
>
> Okay, we can move to the symbolic names.  Do you want them to be that long, or
> would:
>
> nvdimm-cap-cpu
> nvdimm-cap-mem-ctrl
> nvdimm-cap-mirroring

Wait, why is mirroring part of this?

I was thinking this option would be:

    --persistence-domain={cpu,mem-ctrl}

...and try not to let ACPI specifics leak into the qemu command line
interface. For example PowerPC qemu could have a persistence domain
communicated via Open Firmware or some other mechanism.
>
> or something be better?