Re: [PATCH] intel_iommu: Take the bql before registering a new address space

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 15, 2025 at 08:33:30AM -0400, Stefan Hajnoczi wrote:
> On Tue, Apr 15, 2025 at 03:11:00AM -0400, Michael S. Tsirkin wrote:
> > On Tue, Apr 15, 2025 at 06:18:08AM +0000, CLEMENT MATHIEU--DRIF wrote:
> > > Address space creation might end up being called without holding the
> > > bql as it is exposed through the IOMMU ops.
> > > 
> > > Signed-off-by: Clement Mathieu--Drif <clement.mathieu--drif@eviden.com>
> > 
> > 
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > Stefan, want to pick this one up, too?
> 
> Not yet, it may need to wait until after the release:
> - Discussion is still ongoing.
> - Is this a regression in 10.0 or a long-standing issue?
> - Who is affected and what is the impact?

Yea agreed.

> There are still a few hours left before -rc4 is tagged. I will merge it
> if consensus is reached and the missing information becomes clear.
> 
> Thanks,
> Stefan
> 
> > 
> > 
> > > ---
> > >  hw/i386/intel_iommu.c | 10 ++++++++++
> > >  1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > > index dffd7ee885..fea2220013 100644
> > > --- a/hw/i386/intel_iommu.c
> > > +++ b/hw/i386/intel_iommu.c
> > > @@ -4216,6 +4216,7 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus,
> > >      vtd_dev_as = g_hash_table_lookup(s->vtd_address_spaces, &key);
> > >      if (!vtd_dev_as) {
> > >          struct vtd_as_key *new_key = g_malloc(sizeof(*new_key));
> > > +        bool take_bql = !bql_locked();
> > >  
> > >          new_key->bus = bus;
> > >          new_key->devfn = devfn;
> > > @@ -4238,6 +4239,11 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus,
> > >          vtd_dev_as->context_cache_entry.context_cache_gen = 0;
> > >          vtd_dev_as->iova_tree = iova_tree_new();
> > >  
> > > +        /* Some functions in this branch require the bql, make sure we own it */
> > > +        if (take_bql) {
> > > +            bql_lock();
> > > +        }
> > > +
> > >          memory_region_init(&vtd_dev_as->root, OBJECT(s), name, UINT64_MAX);
> > >          address_space_init(&vtd_dev_as->as, &vtd_dev_as->root, "vtd-root");
> > >  
> > > @@ -4305,6 +4311,10 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, PCIBus *bus,
> > >  
> > >          vtd_switch_address_space(vtd_dev_as);
> > >  
> > > +        if (take_bql) {
> > > +            bql_unlock();
> > > +        }
> > > +
> > >          g_hash_table_insert(s->vtd_address_spaces, new_key, vtd_dev_as);
> > >      }
> > >      return vtd_dev_as;
> > > -- 
> > > 2.49.0
> >