Re: [PATCH] vfio/iommu_type1: report the IOMMU aperture info

[Pierre Morel]

On 30/11/2017 15:16, Pierre Morel wrote:
> On 30/11/2017 13:57, Jean-Philippe Brucker wrote:
> > Hello,
> >
> > On 30/11/17 11:34, Pierre Morel wrote:
> > [...]
> > > +/**
> > > + * vfio_get_aperture - report minimal aperture of a vfio_iommu
> > > + * @iommu: the current vfio_iommu
> > > + * @start: a pointer to the aperture start
> > > + * @end  : a pointer to the aperture end
> > > + *
> > > + * This function iterate on the domains using the given vfio_iommu
> > > + * and restrict the aperture to the minimal aperture common
> > > + * to all domains sharing this vfio_iommu.
> > > + */
> > > +static void vfio_get_aperture(struct vfio_iommu *iommu, uint64_t 
> > > *start,
> > > +                uint64_t *end)
> > > +{
> > > +    struct iommu_domain_geometry geometry;
> > > +    struct vfio_domain *domain;
> > > +
> > > +    *start = 0;
> > > +    *end = U64_MAX;
> >
> > I wonder if the default values should also reflect what the VFIO
> > implementation actually supports. Looking at vfio_dma_do_map, a 32-bit
> > host will reject any iova greater than 32 bits. In addition,
> > vfio_dma_do_unmap doesn't support unmapping the last page of a 64-bit
> > address space (existing IOMMUs would probably reject map requests with
> > IOVA > 52 bits anyway, but if they don't report a domain aperture, VFIO
> > can't guess it).
> >
> > I think it's convenient to use VFIO_IOMMU_UNMAP_DMA on the full address
> > space when an unmap-all is needed, maybe we could provide default 
> > aperture
> > values that help doing this? (~0U for 32-bit and (~0ULL - PAGE_SIZE) for
> > 64-bit)


indeed the error is to use uint64_t, I should *never* use this hardware 
specific values but simply unsigned long and -1UL/~0U at this level.

Shouldn't the 52bit problem be reported by the iommu geometry?


> > Thanks,
> > Jean
>
> Thanks, I will take care of this.
>
> Pierre


--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany