[PATCH v2 3/3] RISC-V: KVM: Split huge pages during fault handling for dirty logging

[wang.yechao255 at zte.com.cn]

From: Wang Yechao <wang.yechao255 at zte.com.cn>

During dirty logging, all huge pages are write-protected. When the guest
writes to a write-protected huge page, a page fault is triggered. Before
recovering the write permission, the huge page must be split into smaller
pages (e.g., 4K). After splitting, the normal mapping process proceeds,
allowing write permission to be restored at the smaller page granularity.

This ensures that dirty logging works correctly with huge pages.

Signed-off-by: Wang Yechao <wang.yechao255 at zte.com.cn>
---
 arch/riscv/kvm/gstage.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
index 92331e9b0bb8..27ea6bb81553 100644
--- a/arch/riscv/kvm/gstage.c
+++ b/arch/riscv/kvm/gstage.c
@@ -171,6 +171,9 @@ int kvm_riscv_gstage_map_page(struct kvm_gstage *gstage,
 {
 	pgprot_t prot;
 	int ret;
+	pte_t *ptep;
+	u32 ptep_level;
+	bool found_leaf;

 	out_map->addr = gpa;
 	out_map->level = 0;
@@ -179,6 +182,12 @@ int kvm_riscv_gstage_map_page(struct kvm_gstage *gstage,
 	if (ret)
 		return ret;

+	found_leaf = kvm_riscv_gstage_get_leaf(gstage, gpa, &ptep, &ptep_level);
+	if (found_leaf && ptep_level > out_map->level) {
+		kvm_riscv_gstage_split_huge(gstage, pcache, gpa,
+					    out_map->level, true);
+	}
+
 	/*
 	 * A RISC-V implementation can choose to either:
 	 * 1) Update 'A' and 'D' PTE bits in hardware
-- 
2.47.3