Re: [Xen-devel] [PATCH] iommu: avoid triggering ASSERT_UNREACHABLE() on ARM...

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jan,

On 9/26/19 1:12 PM, Jan Beulich wrote:
> On 26.09.2019 12:03, Paul Durrant wrote:
> > ...when the IOMMU is not enabled.
> >
> > 80ff3d338dc9 "iommu: tidy up iommu_use_hap_pt() and need_iommu_pt_sync()
> > macros" introduced CONFIG_IOMMU_FORCE_PT_SHARE, which causes the global
> > 'iommu_hap_pt_share' option to be replaced with a #define-d value of true.
> > In this configuration, calling clear_iommu_hap_pt_share() will result
> > trigger the aforementioned ASSERT.
> >
> > CONFIG_IOMMU_FORCE_PT_SHARE is always selected for ARM builds and,
> > because clear_iommu_hap_pt_share() is called by the common iommu_setup()
> > function if the IOMMU is not enabled, it is no longer safe to disable the
> > IOMMU on ARM systems.
> >
> > However, running with the IOMMU disabled is a valid configuration for ARM
> > systems, so this patch rectifies the problem by removing the call to
> > clear_iommu_hap_pt_share() from common code. As a side effect of this,
> > however, it becomes possible on x86 systems for iommu_enabled to be false
> > but iommu_hap_pt_share to be true. Thus the code in sysctl.c
> > needs to be changed to make sure that XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share
> > is not erroneously advertised when the IOMMU has been disabled.
> >
> > Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> > Reported-by: Oleksandr <olekstysh@xxxxxxxxx>
> Preferably with the adjustments mantioned elsewhere
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
I have done it while committing the patch.

Cheers,

--
Julien Grall

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