linux-kernel - [PATCH] iommu/exynos: add support for reserved regions

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Message-Id: <20250712-exynos-sysmmu-resv-regions-v1-1-e79681fcab1a@disroot.org>
Date: Sat, 12 Jul 2025 17:19:30 +0530
From: Kaustabh Chakraborty <kauschluss@...root.org>
To: Marek Szyprowski <m.szyprowski@...sung.com>, 
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
 Robin Murphy <robin.murphy@....com>, Krzysztof Kozlowski <krzk@...nel.org>, 
 Alim Akhtar <alim.akhtar@...sung.com>
Cc: iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
 linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Kaustabh Chakraborty <kauschluss@...root.org>
Subject: [PATCH] iommu/exynos: add support for reserved regions

The bootloader configures a reserved memory region for framebuffer,
which is protected by the IOMMU. The kernel-side driver is oblivious as
of which memory region is set up by the bootloader. In such case, the
IOMMU tries to reference the reserved region - which is not reserved in
the kernel anymore - and it results in an unrecoverable page fault. More
information about it is provided in [1].

Add support for reserved regions using iommu_dma_get_resv_regions().
For OF supported boards, this requires defining the region in the
iommu-addresses property of the IOMMU owner's node.

Link: https://lore.kernel.org/r/544ad69cba52a9b87447e3ac1c7fa8c3@disroot.org [1]
Signed-off-by: Kaustabh Chakraborty <kauschluss@...root.org>
---
 drivers/iommu/exynos-iommu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iommu/exynos-iommu.c b/drivers/iommu/exynos-iommu.c
index b62a8f35c3e8516ead6a41f92dc7c8dc057986a8..b6edd178fe25e7c258cc82c47e9170fb4db74064 100644
--- a/drivers/iommu/exynos-iommu.c
+++ b/drivers/iommu/exynos-iommu.c
@@ -22,6 +22,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/slab.h>
 
+#include "dma-iommu.h"
 #include "iommu-pages.h"
 
 typedef u32 sysmmu_iova_t;
@@ -1479,6 +1480,7 @@ static const struct iommu_ops exynos_iommu_ops = {
 	.device_group = generic_device_group,
 	.probe_device = exynos_iommu_probe_device,
 	.release_device = exynos_iommu_release_device,
+	.get_resv_regions = iommu_dma_get_resv_regions,
 	.of_xlate = exynos_iommu_of_xlate,
 	.default_domain_ops = &(const struct iommu_domain_ops) {
 		.attach_dev	= exynos_iommu_attach_device,

---
base-commit: a62b7a37e6fcf4a675b1548e7c168b96ec836442
change-id: 20250629-exynos-sysmmu-resv-regions-661f2889d2d5

Best regards,
-- 
Kaustabh Chakraborty <kauschluss@...root.org>