[RFC PATCH 10/11] iommupt: Add RISC-V dirty tracking PTE ops

[fangyu.yu@linux.alibaba.com]

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

Implement the three dirty-tracking hooks required by the generic page
table framework for the RISC-V format:

  pt_entry_is_write_dirty():
    Check the D bit (bit 7) in the PTE.

  pt_entry_make_write_clean():
    Clear the D bit across the full contiguous range.

  pt_entry_make_write_dirty():
    Atomically set D via try_cmpxchg64() on a single PTE.

Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
---
 drivers/iommu/generic_pt/fmt/riscv.h | 43 ++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/drivers/iommu/generic_pt/fmt/riscv.h b/drivers/iommu/generic_pt/fmt/riscv.h
index 0281356cfaf6..44b87e70f029 100644
--- a/drivers/iommu/generic_pt/fmt/riscv.h
+++ b/drivers/iommu/generic_pt/fmt/riscv.h
@@ -222,6 +222,49 @@ static inline void riscvpt_attr_from_entry(const struct pt_state *pts,
 }
 #define pt_attr_from_entry riscvpt_attr_from_entry
 
+/*
+ * Dirty tracking: RISC-V PTEs use D (bit 7) as the hardware dirty bit.
+ * When Svnapot 64K is active a leaf entry spans 16 consecutive PTEs; we
+ * must check / clear all of them so that no dirty indication is lost.
+ */
+static inline bool riscvpt_entry_is_write_dirty(const struct pt_state *pts)
+{
+	unsigned int num_contig_lg2 = riscvpt_entry_num_contig_lg2(pts);
+	const pt_riscv_entry_t *tablep =
+		pt_cur_table(pts, pt_riscv_entry_t) +
+		log2_set_mod(pts->index, 0, num_contig_lg2);
+	const pt_riscv_entry_t *end = tablep + log2_to_int(num_contig_lg2);
+
+	for (; tablep != end; tablep++)
+		if (READ_ONCE(*tablep) & RISCVPT_D)
+			return true;
+	return false;
+}
+#define pt_entry_is_write_dirty riscvpt_entry_is_write_dirty
+
+static inline void riscvpt_entry_make_write_clean(struct pt_state *pts)
+{
+	unsigned int num_contig_lg2 = riscvpt_entry_num_contig_lg2(pts);
+	pt_riscv_entry_t *tablep =
+		pt_cur_table(pts, pt_riscv_entry_t) +
+		log2_set_mod(pts->index, 0, num_contig_lg2);
+	pt_riscv_entry_t *end = tablep + log2_to_int(num_contig_lg2);
+
+	for (; tablep != end; tablep++)
+		WRITE_ONCE(*tablep, READ_ONCE(*tablep) & ~(pt_riscv_entry_t)RISCVPT_D);
+}
+#define pt_entry_make_write_clean riscvpt_entry_make_write_clean
+
+static inline bool riscvpt_entry_make_write_dirty(struct pt_state *pts)
+{
+	pt_riscv_entry_t *tablep =
+		pt_cur_table(pts, pt_riscv_entry_t) + pts->index;
+	pt_riscv_entry_t new = pts->entry | RISCVPT_D;
+
+	return try_cmpxchg64(tablep, &pts->entry, new);
+}
+#define pt_entry_make_write_dirty riscvpt_entry_make_write_dirty
+
 /* --- iommu */
 #include <linux/generic_pt/iommu.h>
 #include <linux/iommu.h>
-- 
2.50.1