[RFC PATCH v4 09/10] iommu/riscv: Add dirty tracking support for second-stage domains

[fangyu.yu@linux.alibaba.com]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

Add hardware dirty tracking support for second-stage (iohgatp) domains
used in KVM VFIO device pass-through.

The RISC-V IOMMU can automatically set the dirty bit in PTEs on write
access when DC.tc.GADE is set and the hardware has AMO_HWAD capability.
Wire this up to the iommufd dirty tracking interface:

  - riscv_iommu_set_dirty_tracking(): Always enabled dirty tracking for
    second-stage domain.

  - riscv_iommu_dirty_ops: Exposes set_dirty_tracking and the generic
    page-table read_and_clear_dirty via IOMMU_PT_DIRTY_OPS(riscv_64).

  - domain_alloc_paging_flags: Assigns dirty_ops to second-stage domains
    when AMO_HWAD is advertised in hardware capabilities.

  - riscv_iommu_capable: Reports IOMMU_CAP_DIRTY_TRACKING when
    AMO_HWAD is present.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
 drivers/iommu/riscv/iommu.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
index f01fd4e2f840..41b593def1f5 100644
--- a/drivers/iommu/riscv/iommu.c
+++ b/drivers/iommu/riscv/iommu.c
@@ -1352,6 +1352,21 @@ static int riscv_iommu_attach_paging_domain(struct iommu_domain *iommu_domain,
 	return 0;
 }
 
+static int riscv_iommu_set_dirty_tracking(struct iommu_domain *iommu_domain,
+					  bool enable)
+{
+	/*
+	 * Always enabled and the dirty bitmap is cleared prior to
+	 * set_dirty_tracking().
+	 */
+	return 0;
+}
+
+static const struct iommu_dirty_ops riscv_iommu_dirty_ops = {
+	IOMMU_PT_DIRTY_OPS(riscv_64),
+	.set_dirty_tracking = riscv_iommu_set_dirty_tracking,
+};
+
 static const struct iommu_domain_ops riscv_iommu_paging_domain_ops = {
 	IOMMU_PT_DOMAIN_OPS(riscv_64),
 	.attach_dev = riscv_iommu_attach_paging_domain,
@@ -1442,6 +1457,8 @@ riscv_iommu_domain_alloc_paging_flags(struct device *dev, u32 flags,
 			goto err_free;
 		}
 		cfg.common.features |= BIT(PT_FEAT_RISCV_S2);
+		if (iommu->caps & RISCV_IOMMU_CAPABILITIES_AMO_HWAD)
+			domain->domain.dirty_ops = &riscv_iommu_dirty_ops;
 		break;
 	default:
 		ret = -EOPNOTSUPP;
@@ -1517,9 +1534,13 @@ static struct iommu_group *riscv_iommu_device_group(struct device *dev)
 
 static bool riscv_iommu_capable(struct device *dev, enum iommu_cap cap)
 {
+	struct riscv_iommu_device *iommu = dev_to_iommu(dev);
+
 	switch (cap) {
 	case IOMMU_CAP_CACHE_COHERENCY:
 		return true;
+	case IOMMU_CAP_DIRTY_TRACKING:
+		return !!(iommu->caps & RISCV_IOMMU_CAPABILITIES_AMO_HWAD);
 	default:
 		return false;
 	}
-- 
2.50.1