linux-kernel - [PATCH] iommu/amd: Stop irq_remapping_select() matching when remapping is disabled

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Date:   Tue, 05 Jan 2021 01:36:13 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Johnathan Smithinovic <johnathan.smithinovic@....at>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        iommu <iommu@...ts.linux-foundation.org>,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>
Subject: [PATCH] iommu/amd: Stop irq_remapping_select() matching when
 remapping is disabled

From: David Woodhouse <dwmw@...zon.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 irqdomain")
Reported-by: Johnathan Smithinovic <johnathan.smithinovic@....at>
Signed-off-by: David Woodhouse <dwmw@...zon.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 = -1;

+	if (!amd_iommu_irq_remap)
+		return 0;
+
 	if (x86_fwspec_is_ioapic(fwspec))
 		devid = get_ioapic_devid(fwspec->param[0]);
 	else if (x86_fwspec_is_hpet(fwspec))
-- 
2.29.2

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