Re: [PATCH for-4.12] xen/iommu: fix dev assignment on ARM after 91d4eca7

[Stefano Stabellini <sstabellini@kernel.org>]

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On Thu, 3 Jan 2019, Andrew Cooper wrote:
> On 03/01/2019 00:28, Stefano Stabellini wrote:
> > Fix device assignment on ARM after 91d4eca7 "mm / iommu: split
> > need_iommu() into has_iommu_pt() and need_iommu_pt_sync()".
> >
> > arch_iommu_populate_page_table returns -ENOSYS which causes
> > iommu_construct to return early, although it is not an error.
> >
> > Interestingly, the if ( rc ) was present even before 91d4eca7, but it was
> > still working before. Now, with the new hd->status field it won't
> > complete the initialization successfully.
> >
> > Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
> >
> > diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
> > index ac62d7f..a63329b 100644
> > --- a/xen/drivers/passthrough/iommu.c
> > +++ b/xen/drivers/passthrough/iommu.c
> > @@ -269,7 +269,7 @@ int iommu_construct(struct domain *d)
> >          hd->need_sync = true;
> >  
> >          rc = arch_iommu_populate_page_table(d);
> 
> The comment in ARM's arch_iommu_populate_page_table() says
> 
> /* The IOMMU shares the p2m with the CPU */
> 
> Which means that iommu_use_hap_pt() (just out of context above this
> hunk) is wrong.  It should return true, which will prevent us entering
> this path during initialisation.

iommu_use_hap_pt is implemented by calling has_iommu_pt(d) (also on x86
is part of the implementation), which is implemented as:

  (dom_iommu(d)->status != IOMMU_STATUS_disabled)

IOMMU_STATUS_disabled is zero in the enum, so status starts as
IOMMU_STATUS_disabled. It is set to IOMMU_STATUS_initializing for dom0
in iommu_hwdom_init, but it is not set to IOMMU_STATUS_initializing for
other domains anywhere, leading to this error.

It looks like we want to move the initialization of status from
iommu_hwdom_init to iommu_domain_init, which is called for everybody.


diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index ac62d7f..7cf6aaf 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -180,6 +180,7 @@ int iommu_domain_init(struct domain *d)
     if ( !iommu_enabled )
         return 0;
 
+    hd->status = IOMMU_STATUS_initializing;
     hd->platform_ops = iommu_get_ops();
     return hd->platform_ops->init(d);
 }
@@ -206,7 +207,6 @@ void __hwdom_init iommu_hwdom_init(struct domain *d)
 
     register_keyhandler('o', &iommu_dump_p2m_table, "dump iommu p2m table", 0);
 
-    hd->status = IOMMU_STATUS_initializing;
     hd->need_sync = iommu_hwdom_strict && !iommu_use_hap_pt(d);
     if ( need_iommu_pt_sync(d) )
     {

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