[PATCH v2 09/14] iommu/riscv: Publish IOMMU_RESV_SW_MSI region for iommufd MSI remapping

[Andrew Jones]

iommufd's SW MSI path (iommufd_sw_map_msi) requires an IOMMU_RESV_SW_MSI
reservation region to know the IOVA base (sw_msi_start) for MSI page
mappings. Without it, sw_msi_start stays at PHYS_ADDR_MAX and
iommufd_sw_map_msi silently returns passthrough.

Add a get_resv_regions callback that, when IMSIC-based MSI is in use,
reserves an IOVA range of num_possible_cpus() pages starting at
RISCV_IOMMU_MSI_IOVA_BASE. This is large enough to hold one 4 KiB
IMSIC supervisor page per hart.

RISCV_IOMMU_MSI_IOVA_BASE is set to 128 MiB, matching the ARM SMMU
convention. That value is arbitrary for ARM too; its introducing commit
(f3ebee80b313) calls it an "arbitrary MSI IOVA window", so there is
nothing riscv-specific lost by reusing it here.

Signed-off-by: Andrew Jones <andrew.jones@xxxxxxxxxxxxxxxx>
---
 drivers/iommu/riscv/iommu.c | 16 ++++++++++++++++
 drivers/iommu/riscv/iommu.h |  3 +++
 2 files changed, 19 insertions(+)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index 27dfd60834ac..98ce9ec50e65 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -1493,6 +1493,21 @@ static void riscv_iommu_release_device(struct device *dev)
 	kfree_rcu_mightsleep(info);
 }
 
+static void riscv_iommu_get_resv_regions(struct device *dev, struct list_head *head)
+{
+	struct iommu_resv_region *region;
+
+	if (!imsic_enabled())
+		return;
+
+	region = iommu_alloc_resv_region(RISCV_IOMMU_MSI_IOVA_BASE,
+					 (size_t)num_possible_cpus() * PAGE_SIZE,
+					 IOMMU_WRITE | IOMMU_NOEXEC | IOMMU_MMIO,
+					 IOMMU_RESV_SW_MSI, GFP_KERNEL);
+	if (region)
+		list_add_tail(&region->list, head);
+}
+
 static const struct iommu_ops riscv_iommu_ops = {
 	.of_xlate = riscv_iommu_of_xlate,
 	.identity_domain = &riscv_iommu_identity_domain,
@@ -1502,6 +1517,7 @@ static const struct iommu_ops riscv_iommu_ops = {
 	.device_group = riscv_iommu_device_group,
 	.probe_device = riscv_iommu_probe_device,
 	.release_device	= riscv_iommu_release_device,
+	.get_resv_regions = riscv_iommu_get_resv_regions,
 };
 
 static int riscv_iommu_init_check(struct riscv_iommu_device *iommu)
diff --git a/drivers/iommu/riscv/iommu.h b/drivers/iommu/riscv/iommu.h
index ded18aec8010..9a8fd5300675 100644
--- a/drivers/iommu/riscv/iommu.h
+++ b/drivers/iommu/riscv/iommu.h
@@ -20,6 +20,9 @@
 
 #include "iommu-bits.h"
 
+/* IOVA base for the SW MSI reservation; same convention as ARM SMMU. */
+#define RISCV_IOMMU_MSI_IOVA_BASE	SZ_128M
+
 /* This struct contains protection domain specific IOMMU driver data. */
 struct riscv_iommu_domain {
 	union {
-- 
2.43.0