Re: [Xen-devel] [RFC][v2][PATCH 01/14] tools: introduce some new parameters to set rdm policy

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2015/6/7 19:06, Wei Liu wrote:
> On Wed, Jun 03, 2015 at 09:35:16AM +0800, Chen, Tiejun wrote:
> [...]
> > > > +reserved regions explicitly. And using "host" to include all reserved regions
> > > > +reported on this platform which is good to handle hotplug scenario. In the
> > > > +future this parameter may be further extended to allow specifying random
> > > > +regions, e.g. even those belonging to another platform as a preparation
> > > Extending how? What's your envisaged syntax for those random regions?
> > We didn't go into details while discussing that design. Maybe we can do
> > something like this,
> >
> > rdm="type=host,reserve=strict,rdm_add=size[KMG][@offset[KMG]],size[KMG][@offset[KMG]],..."
> This limits the extra regions to type host and strict policy. If that's
> what you want then it's fine.
The policy still can be changed with "reserve=". But whatever, I mean 
this current format is easy to extend :) You know, the hotplug is really 
a complicated case, we really need to consider more next.
Thanks
Tiejun

> > > Should you want to reserve more, an array is more useful. Could you
> > Yeah.
> >
> > > provide some examples?
> > But we may have alternative approach to this when I noticed some guys are
> > trying to delivery some patches about setting rmrr region by xen
> > commandline. So I also would like to check this likelihood when we can step
> > forward.
> Makes sense.
>
> > > > +for live migration with passthrough devices.
> > > > +
> > > > +"none" means we have nothing to do all reserved regions and ignore all 
> > > > policies,
> > > > +so guest work as before.
> [...]
>
> > > > diff --git a/docs/misc/vtd.txt b/docs/misc/vtd.txt
> > > > index 9af0e99..7d63c47 100644
> > > > --- a/docs/misc/vtd.txt
> > > > +++ b/docs/misc/vtd.txt
> > > > @@ -111,6 +111,30 @@ in the config file:
> > > >   To override for a specific device:
> > > >         pci = [ '01:00.0,msitranslate=0', '03:00.0' ]
> > > >
> > > > +RDM, 'reserved device memory', for PCI Device Passthrough
> > > > +---------------------------------------------------------
> > > > +
> > > > +There are some devices the BIOS controls, for e.g. USB devices to perform
> > > > +PS2 emulation. The regions of memory used for these devices are marked
> > > > +reserved in the e820 map. When we turn on DMA translation, DMA to those
> > > > +regions will fail. Hence BIOS uses RMRR to specify these regions along with
> > > > +devices that need to access these regions. OS is expected to setup
> > > > +identity mappings for these regions for these devices to access these regions.
> > > > +
> > > > +While creating a VM we should reserve them in advance, and avoid any conflicts.
> > > > +So we introduce user configurable parameters to specify RDM resource and
> > > > +according policies,
> > > > +
> > > > +To enable this globally, add "rdm" in the config file:
> > > > +
> > > > +    rdm = "type=host, reserve=relaxed"   (default policy is "relaxed")
> > > > +
> > > > +Or just for a specific device:
> > > > +
> > > > +    pci = [ '01:00.0,rdm_reserve=relaxed', '03:00.0,rdm_reserve=strict' ]
> > > > +
> > > > +For all the options available to RDM, see xl.cfg(5).
> > > > +
> > > >
> > > >   Caveat on Conventional PCI Device Passthrough
> > > >   ---------------------------------------------
> > > > diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
> > > > index f0da7dc..d649ead 100644
> > > > --- a/tools/libxl/libxl_create.c
> > > > +++ b/tools/libxl/libxl_create.c
> > > > @@ -100,6 +100,12 @@ static int sched_params_valid(libxl__gc *gc,
> > > >       return 1;
> > > >   }
> > > >
> > > > +void libxl__rdm_setdefault(libxl__gc *gc, libxl_domain_build_info *b_info)
> > > > +{
> > > > +    b_info->rdm.type = LIBXL_RDM_RESERVE_TYPE_NONE;
> > Based on our previous discussion, I will initial this firstly,
> >
> > +libxl_rdm_reserve_type = Enumeration("rdm_reserve_type", [
> > +    (0, "none"),
> > +    (1, "host"),
> > +    ], init_val = "LIBXL_RDM_RESERVE_TYPE_NONE")
> > +
> >
> > and then, I would remove this line since right now we just own two options,
> > "none" or "host". And both they're fine.
> >
> > > > +    b_info->rdm.reserve = LIBXL_RDM_RESERVE_FLAG_RELAXED;
> > > No, not like this. You set everything back to none and relaxed even if
> > > it is set before this point.
> > >
> > > It should be
> > >      if (xxx == DEFAULT_SENTINEL_VALUE)
> > >          xxx = THE_DEFAULT_YOU_WANT;
> > >
> > > Have a look at libxl__device_nic_setdefault etc to get an idea
> > > how it works. Don't hesitate to ask if I'm not clear enough.
> > But indeed, here we should set rdm.reserve as you said,
> >
> > +void libxl__rdm_setdefault(libxl__gc *gc, libxl_domain_build_info *b_info)
> > +{
> > +    if (b_info->rdm.reserve == LIBXL_RDM_RESERVE_FLAG_INVALID)
> > +        b_info->rdm.reserve = LIBXL_RDM_RESERVE_FLAG_RELAXED;
> > +}
> > +
> Yes. This is fine.
>
> Wei.
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