Re: [Xen-devel] [PATCH 0/2] Dangling fixes for ARM iommu

[Julien Grall <julien.grall@xxxxxxx>]

On 23/01/2019 17:53, Andrii Anisov wrote:
> Hello Julien,
Hi,

> On 22.01.19 16:31, Julien Grall wrote:
> > > IMO, the pure fixes, like patch 2, and the first hunk of patch 1 should be OK 
> > > for 4.12.
> > The first hunk of patch 1 aside, we never supported the new IOMMU bindings nor 
> > unsharing the P2M. So what do you actually fix?
> > Supporting unshared P2M will require more work given because the code relies 
> > on mfn_to_gmfn that is not implemented on Arm. So accepting this patch 
> > standalone would be misleading as the rest of the series is not going to be 
> > merged in Xen 4.12.
> I'm not saying I want something from non-shared p2m push into 4.12.
I know and this is not what I implied in my previous e-mail. I pointed out that 
the rest of the series is not planned for Xen 4.12, hence it does not make sense 
to get that patch merged.
> I would strip the first patch to its first chunk.
I can queue the first hunk for Xen 4.13.

> > Similarly, we don't support new IOMMU bindings. The patch #2 alone is going to 
> > add more trouble as now Dom0 would not be able to use the IOMMU if it were not 
> > hidden.
> Are you sure we should pass IOMMU devices or related info to Dom0 if they are 
> not supported by hypervisor?
> The commit message states "We don't passthrough IOMMU device to DOM0 even if it 
> is not used by Xen.", and you agreed that some time ago. Could you please 
> clarify why you have changed your mind?
This statement is only correct if the IOMMU has been actively blacklisted by 
Xen. In the case of the SMMU driver, this is done by arm_smmu_dt_init(). The 
function is only called when the IOMMU has been enabled.
So if you pass "iommu=disabled" to Xen commandline, the SMMU will be accessible 
by Dom0.
When there are no drivers for the IOMMU used, then you end up to assign the 
IOMMU to Dom0. This means that Dom0 can use them.
It does not make sense to remove the properties "iommus", "iommu-map", 
"iommu-map-mask" if Dom0 is already touching the IOMMU. It is either everything 
or nothing.
Cheers,

--
Julien Grall

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