RE: [PATCH 5/6] iommu: remove the share_p2m operation

["Durrant, Paul" <pdurrant@amazon.co.uk>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: 26 July 2020 09:50
> To: Paul Durrant <paul@xen.org>
> Cc: xen-devel@lists.xenproject.org; Durrant, Paul <pdurrant@amazon.co.uk>; Andrew Cooper
> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Wei Liu <wl@xen.org>; Roger Pau
> Monné <roger.pau@citrix.com>; Kevin Tian <kevin.tian@intel.com>
> Subject: RE: [EXTERNAL] [PATCH 5/6] iommu: remove the share_p2m operation
> 
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> 
> 
> On 24.07.2020 18:46, Paul Durrant wrote:
> > --- a/xen/drivers/passthrough/vtd/iommu.c
> > +++ b/xen/drivers/passthrough/vtd/iommu.c
> > @@ -313,6 +313,26 @@ static u64 addr_to_dma_page_maddr(struct domain *domain, u64 addr, int alloc)
> >      return pte_maddr;
> >  }
> >
> > +static u64 domain_pgd_maddr(struct domain *d)
> 
> uint64_t please.
> 

Ok.

> > +{
> > +    struct domain_iommu *hd = dom_iommu(d);
> > +
> > +    ASSERT(spin_is_locked(&hd->arch.mapping_lock));
> > +
> > +    if ( iommu_use_hap_pt(d) )
> > +    {
> > +        mfn_t pgd_mfn =
> > +            pagetable_get_mfn(p2m_get_pagetable(p2m_get_hostp2m(d)));
> > +
> > +        return pagetable_get_paddr(pagetable_from_mfn(pgd_mfn));
> > +    }
> > +
> > +    if ( !hd->arch.vtd.pgd_maddr )
> > +        addr_to_dma_page_maddr(d, 0, 1);
> > +
> > +    return hd->arch.vtd.pgd_maddr;
> > +}
> > +
> >  static void iommu_flush_write_buffer(struct vtd_iommu *iommu)
> >  {
> >      u32 val;
> > @@ -1347,22 +1367,17 @@ int domain_context_mapping_one(
> >      {
> >          spin_lock(&hd->arch.mapping_lock);
> >
> > -        /* Ensure we have pagetables allocated down to leaf PTE. */
> > -        if ( hd->arch.vtd.pgd_maddr == 0 )
> > +        pgd_maddr = domain_pgd_maddr(domain);
> > +        if ( !pgd_maddr )
> >          {
> > -            addr_to_dma_page_maddr(domain, 0, 1);
> > -            if ( hd->arch.vtd.pgd_maddr == 0 )
> > -            {
> > -            nomem:
> > -                spin_unlock(&hd->arch.mapping_lock);
> > -                spin_unlock(&iommu->lock);
> > -                unmap_vtd_domain_page(context_entries);
> > -                return -ENOMEM;
> > -            }
> > +        nomem:
> > +            spin_unlock(&hd->arch.mapping_lock);
> > +            spin_unlock(&iommu->lock);
> > +            unmap_vtd_domain_page(context_entries);
> > +            return -ENOMEM;
> >          }
> 
> This renders all calls bogus in shared mode - the function, if
> it ended up getting called nevertheless, would then still alloc
> the root table. Therefore I'd like to suggest that at least all
> its callers get an explicit check. That's really just
> dma_pte_clear_one() as it looks.
> 

Ok, I think I may move this code out into a separate function too since the nomem label is slightly awkward, so I'll re-factor it.

  Paul

> Jan