Re: [PATCH v2 3/3] [FUTURE] xen/arm: enable vPCI for domUs

["Roger Pau Monné" <roger.pau@citrix.com>]

On Fri, Jul 07, 2023 at 10:00:51AM +0100, Julien Grall wrote:
> On 07/07/2023 02:47, Stewart Hildebrand wrote:
> > Note that CONFIG_HAS_VPCI_GUEST_SUPPORT is not currently used in the upstream
> > code base. It will be used by the vPCI series [1]. This patch is intended to be
> > merged as part of the vPCI series.
> > 
> > v1->v2:
> > * new patch
> > ---
> >   xen/arch/arm/Kconfig              | 1 +
> >   xen/arch/arm/include/asm/domain.h | 2 +-
> >   2 files changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> > index 4e0cc421ad48..75dfa2f5a82d 100644
> > --- a/xen/arch/arm/Kconfig
> > +++ b/xen/arch/arm/Kconfig
> > @@ -195,6 +195,7 @@ config PCI_PASSTHROUGH
> >   	depends on ARM_64
> >   	select HAS_PCI
> >   	select HAS_VPCI
> > +	select HAS_VPCI_GUEST_SUPPORT
> >   	default n
> >   	help
> >   	  This option enables PCI device passthrough
> > diff --git a/xen/arch/arm/include/asm/domain.h b/xen/arch/arm/include/asm/domain.h
> > index 1a13965a26b8..6e016b00bae1 100644
> > --- a/xen/arch/arm/include/asm/domain.h
> > +++ b/xen/arch/arm/include/asm/domain.h
> > @@ -298,7 +298,7 @@ static inline void arch_vcpu_block(struct vcpu *v) {}
> >   #define arch_vm_assist_valid_mask(d) (1UL << VMASST_TYPE_runstate_update_flag)
> > -#define has_vpci(d) ({ IS_ENABLED(CONFIG_HAS_VPCI) && is_hardware_domain(d); })
> > +#define has_vpci(d)    ({ (void)(d); IS_ENABLED(CONFIG_HAS_VPCI); })
> 
> As I mentioned in the previous patch, wouldn't this enable vPCI
> unconditionally for all the domain? Shouldn't this be instead an optional
> feature which would be selected by the toolstack?

I do think so, at least on x86 we signal whether vPCI should be
enabled for a domain using xen_arch_domainconfig at domain creation.

Ideally we would like to do this on a per-device basis for domUs, so
we should consider adding a new flag to xen_domctl_assign_device in
order to signal whether the assigned device should use vPCI.

Thanks, Roger.