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Message-ID: <04bbe8bca87f81a3cfa93ec4299e53f47e00e5b3.camel@infradead.org>
Subject: [PATCH] iommu/amd: Stop irq_remapping_select() matching when
 remapping is disabled
From:   David Woodhouse <dwmw2@infradead.org>
To:     Johnathan Smithinovic <johnathan.smithinovic@gmx.at>,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        iommu <iommu@lists.linux-foundation.org>,
        Will Deacon <will@kernel.org>, Joerg Roedel <joro@8bytes.org>
Date:   Tue, 05 Jan 2021 01:36:13 +0000
In-Reply-To: <ed4be9b4-24ac-7128-c522-7ef359e8185d@gmx.at>
References: <ed4be9b4-24ac-7128-c522-7ef359e8185d@gmx.at>
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From: David Woodhouse <dwmw@amazon.co.uk>

The AMD IOMMU initialisation registers the IRQ remapping domain for
each IOMMU before doing the final sanity check that every I/OAPIC is
covered.

This means that the AMD irq_remapping_select() function gets invoked
even when IRQ remapping has been disabled, eventually leading to a NULL
pointer dereference in alloc_irq_table().

Unfortunately, the IVRS isn't fully parsed early enough that the sanity
check can be done in time to registering the IRQ domain altogether.
Doing that would be nice, but is a larger and more error-prone task. The
simple fix is just for irq_remapping_select() to refuse to report a
match when IRQ remapping has disabled.

Link: https://lore.kernel.org/lkml/ed4be9b4-24ac-7128-c522-7ef359e8185d@gmx=
.at
Fixes: a1a785b57242 ("iommu/amd: Implement select() method on remapping irq=
domain")
Reported-by: Johnathan Smithinovic <johnathan.smithinovic@gmx.at>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 drivers/iommu/amd/iommu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 7e2c445a1fae..f0adbc48fd17 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -3854,6 +3854,9 @@ static int irq_remapping_select(struct irq_domain *d,=
 struct irq_fwspec *fwspec,
 	struct amd_iommu *iommu;
 	int devid =3D -1;
=20
+	if (!amd_iommu_irq_remap)
+		return 0;
+
 	if (x86_fwspec_is_ioapic(fwspec))
 		devid =3D get_ioapic_devid(fwspec->param[0]);
 	else if (x86_fwspec_is_hpet(fwspec))
--=20
2.29.2


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