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Date:   Mon, 11 May 2020 22:16:56 +0200
From:   Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= <uwe@kleine-koenig.org>
To:     Lu Baolu <baolu.lu@linux.intel.com>, Joerg Roedel <jroedel@suse.de>
Cc:     linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com,
        tglx@linutronix.de, x86@kernel.org
Subject: Re: Failure to shutdown/reboot with intel_iommu=on
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Hello again,

On Mon, May 11, 2020 at 09:59:31PM +0200, Uwe Kleine-K=F6nig wrote:
> On 5/9/20 3:58 AM, Lu Baolu wrote:
> > Hi Uwe,
> >=20
> > Have you tried commenting out intel_disable_iommus() in
> > intel_iommu_shutdowan()?
> >=20
> > 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)
> > =A0=A0=A0=A0=A0=A0=A0 for_each_iommu(iommu, drhd)
> > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 iommu_disable_protect_mem=
_regions(iommu);
> >=20
> > +#if 0
> > =A0=A0=A0=A0=A0=A0=A0 /* Make sure the IOMMUs are switched off */
> > =A0=A0=A0=A0=A0=A0=A0 intel_disable_iommus();
> > +#endif
> >=20
> > =A0=A0=A0=A0=A0=A0=A0 up_write(&dmar_global_lock);
> > =A0}
>=20
> 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;
=20
+	pr_warn("%s:%d\n", __func__, __LINE__);
 	down_write(&dmar_global_lock);
=20
+	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__);
+	}
=20
+	pr_warn("%s:%d\n", __func__, __LINE__);
 	/* Make sure the IOMMUs are switched off */
 	intel_disable_iommus();
=20
+	pr_warn("%s:%d\n", __func__, __LINE__);
 	up_write(&dmar_global_lock);
+	pr_warn("%s:%d\n", __func__, __LINE__);
 }
=20
 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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