Re: [Xen-devel] [PATCH] intel/iommu: setup inclusive mappings before enabling iommu

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.09.18 at 13:06, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Sep 14, 2018 at 04:49:49AM -0600, Jan Beulich wrote:
>> >>> On 14.09.18 at 11:54, <roger.pau@xxxxxxxxxx> wrote:
>> > On Fri, Sep 14, 2018 at 03:06:03AM -0600, Jan Beulich wrote:
>> >> >>> On 14.09.18 at 10:02, <roger.pau@xxxxxxxxxx> wrote:
>> >> > This restores the behavior before commit 66a9274cc3435 that changed
>> >> > the order and enabled the iommu without having the inclusive mappings
>> >> > setup.
>> >> > 
>> >> > Note that in order to restore previous behavior a new enable hook is
>> >> > added to the iommu_ops struct that's only used by VT-d.
>> >> 
>> >> But your earlier series also extends inclusive mapping support to AMD -
>> >> why is there no similar change needed there in case someone overrides
>> >> the default of off in that case?
>> > 
>> > I don't see any iommu enable related code in amd_iommu_hwdom_init, but
>> > maybe I'm missing something (same applies to ARM SMMU). AFAICT for AMD
>> > the iommu is initialized in iommu_setup which happens before Dom0
>> > creation.
>> 
>> But isn't the problem here that the IOMMU gets enabled too early?
> 
> For Intel yes, my earlier series changed the order for Intel and the
> IOMMU got initialized before setting the inclusive mappings.
> 
>> Who or what tells us this isn't a problem on AMD as well (which then
>> would be another regression of your earlier series, not the patch
>> here, but would presumably also want fixing here)?
> 
> My earlier series only changed the initialization order of the Intel
> IOMMU, AMD IOMMU has always been initialized earlier in iommu_setup,
> and that's not changed.

But prior to that series, the command line parameter was private to
xen/drivers/passthrough/vtd/x86/vtd.c. You've insisted on making
the option available on AMD, but if it is to be of any use, ordering
there likely needs to match that for VT-d.

Jan



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