Re: [PATCH 01/10] iommu/ioasid: Introduce system-wide capacity

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Hi Jean,

On Wed, 1 Apr 2020 15:45:52 +0200
Jean-Philippe Brucker <jean-philippe@linaro.org> wrote:

> On Wed, Mar 25, 2020 at 10:55:22AM -0700, Jacob Pan wrote:
> > IOASID is a limited system-wide resource that can be allocated at
> > runtime. This limitation can be enumerated during boot. For
> > example, on x86 platforms, PCI Process Address Space ID (PASID)
> > allocation uses IOASID service. The number of supported PASID bits
> > are enumerated by extended capability register as defined in the
> > VT-d spec.
> > 
> > This patch adds a helper to set the system capacity, it expected to
> > be set during boot prior to any allocation request.  
> 
> This one-time setting is a bit awkward. Since multiple IOMMU drivers
> may be loaded, this can't be a module_init() thing. And we generally
> have multiple SMMU instances in the system. So we'd need to call
> install_capacity() only for the first SMMU loaded with an arbitrary
> 1<<20, even though each SMMU can support different numbers of PASID
> bits. Furthermore, modules such as iommu-sva will want to initialize
> their IOASID set at module_init(), which will happen before the SMMU
> can set up the capacity, so ioasid_alloc_set() will return an error.
> 
> How about hardcoding ioasid_capacity to 20 bits for now?  It's the
> PCIe limit and probably won't have to increase for a while.
> 
Sound good. Default to 20 bits but can be adjusted if needed.
 

> Thanks,
> Jean
> 
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> >  drivers/iommu/ioasid.c | 15 +++++++++++++++
> >  include/linux/ioasid.h |  5 ++++-
> >  2 files changed, 19 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> > index 0f8dd377aada..4026e52855b9 100644
> > --- a/drivers/iommu/ioasid.c
> > +++ b/drivers/iommu/ioasid.c
> > @@ -17,6 +17,21 @@ struct ioasid_data {
> >  	struct rcu_head rcu;
> >  };
> >  
> > +static ioasid_t ioasid_capacity;
> > +static ioasid_t ioasid_capacity_avail;
> > +
> > +/* System capacity can only be set once */
> > +void ioasid_install_capacity(ioasid_t total)
> > +{
> > +	if (ioasid_capacity) {
> > +		pr_warn("IOASID capacity already set at %d\n",
> > ioasid_capacity);
> > +		return;
> > +	}
> > +
> > +	ioasid_capacity = ioasid_capacity_avail = total;
> > +}
> > +EXPORT_SYMBOL_GPL(ioasid_install_capacity);
> > +
> >  /*
> >   * struct ioasid_allocator_data - Internal data structure to hold
> > information
> >   * about an allocator. There are two types of allocators:
> > diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> > index 6f000d7a0ddc..9711fa0dc357 100644
> > --- a/include/linux/ioasid.h
> > +++ b/include/linux/ioasid.h
> > @@ -40,7 +40,7 @@ void *ioasid_find(struct ioasid_set *set,
> > ioasid_t ioasid, int ioasid_register_allocator(struct
> > ioasid_allocator_ops *allocator); void
> > ioasid_unregister_allocator(struct ioasid_allocator_ops
> > *allocator); int ioasid_set_data(ioasid_t ioasid, void *data); -
> > +void ioasid_install_capacity(ioasid_t total);
> >  #else /* !CONFIG_IOASID */
> >  static inline ioasid_t ioasid_alloc(struct ioasid_set *set,
> > ioasid_t min, ioasid_t max, void *private)
> > @@ -72,5 +72,8 @@ static inline int ioasid_set_data(ioasid_t
> > ioasid, void *data) return -ENOTSUPP;
> >  }
> >  
> > +static inline void ioasid_install_capacity(ioasid_t total)
> > +{
> > +}
> >  #endif /* CONFIG_IOASID */
> >  #endif /* __LINUX_IOASID_H */
> > -- 
> > 2.7.4
> >   

[Jacob Pan]
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