Re: Failure to shutdown/reboot with intel_iommu=on

[Uwe Kleine-König]

Hello again,

On Mon, May 11, 2020 at 09:59:31PM +0200, Uwe Kleine-König wrote:
> On 5/9/20 3:58 AM, Lu Baolu wrote:
> > Hi Uwe,
> > 
> > Have you tried commenting out intel_disable_iommus() in
> > intel_iommu_shutdowan()?
> > 
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index 0182cff2c7ac..532e62600f95 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -4928,8 +4928,10 @@ void intel_iommu_shutdown(void)
> >         for_each_iommu(iommu, drhd)
> >                 iommu_disable_protect_mem_regions(iommu);
> > 
> > +#if 0
> >         /* Make sure the IOMMUs are switched off */
> >         intel_disable_iommus();
> > +#endif
> > 
> >         up_write(&dmar_global_lock);
> >  }
> 
> I just tested that and it didn't help. The machine still hangs with the
> same symptoms as reported before.

I patched the file a bit differently:

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index ef0a5246700e..b76acae6a6ac 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4922,16 +4922,24 @@ void intel_iommu_shutdown(void)
        if (no_iommu || dmar_disabled)
                return;
 
+       pr_warn("%s:%d\n", __func__, __LINE__);
        down_write(&dmar_global_lock);
 
+       pr_warn("%s:%d\n", __func__, __LINE__);
        /* Disable PMRs explicitly here. */
-       for_each_iommu(iommu, drhd)
+       for_each_iommu(iommu, drhd) {
+               pr_warn("%s:%d\n", __func__, __LINE__);
                iommu_disable_protect_mem_regions(iommu);
+               pr_warn("%s:%d\n", __func__, __LINE__);
+       }
 
+       pr_warn("%s:%d\n", __func__, __LINE__);
        /* Make sure the IOMMUs are switched off */
        intel_disable_iommus();
 
+       pr_warn("%s:%d\n", __func__, __LINE__);
        up_write(&dmar_global_lock);
+       pr_warn("%s:%d\n", __func__, __LINE__);
 }
 
 static inline struct intel_iommu *dev_to_intel_iommu(struct device *dev)

and the output shows that the for_each_iommu loop runs twice and the
last pr_warn is reached, too. So the hang doesn't occur in
intel_iommu_shutdown() but later.

I don't know enough about x86 and iommus to judge what that means or
even if this was a useful test.

Best regards
Uwe

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