[PATCH v3 3/3] KVM: riscv: Register ptdump with debugfs on guest creation

["Dylan.Wu" <fredwudi0305@gmail.com>]

Implement the gstage page table dumper for RISC-V KVM, which exposes
the guest's gstage page tables via debugfs. When
CONFIG_PTDUMP_GSTAGE_DEBUGFS is enabled, a "gstage_page_tables" file
will be created under each VM's debugfs directory.

This reuses the ptdump framework from the kernel page table dumper,
with gstage-specific attribute bits and level definitions.

Assisted-by: YuanSheng: deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Dylan.Wu <fredwudi0305@gmail.com>
---
 arch/riscv/kvm/Kconfig  |  12 +++
 arch/riscv/kvm/Makefile |   1 +
 arch/riscv/kvm/ptdump.c | 177 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 190 insertions(+)
 create mode 100644 arch/riscv/kvm/ptdump.c

diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
index ec2cee0a3..6d62b967f 100644
--- a/arch/riscv/kvm/Kconfig
+++ b/arch/riscv/kvm/Kconfig
@@ -37,4 +37,16 @@ config KVM
 
 	  If unsure, say N.
 
+config PTDUMP_GSTAGE_DEBUGFS
+	bool "Present the gstage pagetables to debugfs"
+	depends on KVM && DEBUG_KERNEL && DEBUG_FS && PTDUMP_DEBUGFS
+	default n
+	help
+	  Say Y here if you want to show the RISC-V KVM gstage guest
+	  page tables in debugfs under each VM's debugfs directory as
+	  a file named "gstage_page_tables". This allows inspection of
+	  the second-stage address translation setup for each guest.
+
+	  If unsure, say N.
+
 endif # VIRTUALIZATION
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index 296c2ba05..905593d6f 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -19,6 +19,7 @@ kvm-y += isa.o
 kvm-y += main.o
 kvm-y += mmu.o
 kvm-y += nacl.o
+kvm-$(CONFIG_PTDUMP_GSTAGE_DEBUGFS) += ptdump.o
 kvm-y += tlb.o
 kvm-y += vcpu.o
 kvm-y += vcpu_config.o
diff --git a/arch/riscv/kvm/ptdump.c b/arch/riscv/kvm/ptdump.c
new file mode 100644
index 000000000..f436ad48c
--- /dev/null
+++ b/arch/riscv/kvm/ptdump.c
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024 SiFive
+ */
+
+#include <linux/debugfs.h>
+#include <linux/ptdump.h>
+#include <linux/seq_file.h>
+
+#include <linux/kvm_host.h>
+#include <asm/kvm_gstage.h>
+#include <asm/pgtable.h>
+#include <asm/ptdump.h>
+
+enum gstage_address_markers_idx {
+	GSTAGE_GPA_START_NR,
+	GSTAGE_GPA_END_NR,
+	END_OF_GSTAGE_SPACE_NR
+};
+
+static const struct ptdump_prot_bits gstage_pte_bits[] = {
+	{
+		.mask = _PAGE_DIRTY,
+		.set = "D",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_ACCESSED,
+		.set = "A",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_GLOBAL,
+		.set = "G",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_USER,
+		.set = "U",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_EXEC,
+		.set = "X",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_WRITE,
+		.set = "W",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_READ,
+		.set = "R",
+		.clear = ".",
+	}, {
+		.mask = _PAGE_PRESENT,
+		.set = "V",
+		.clear = ".",
+	}
+};
+
+static struct ptdump_pg_level gstage_pg_levels[] = {
+	{ /* pgd */
+		.bits = gstage_pte_bits,
+		.num = ARRAY_SIZE(gstage_pte_bits),
+		.name = "PGD",
+	}, { /* p4d */
+		.bits = gstage_pte_bits,
+		.num = ARRAY_SIZE(gstage_pte_bits),
+		.name = "P4D",
+	}, { /* pud */
+		.bits = gstage_pte_bits,
+		.num = ARRAY_SIZE(gstage_pte_bits),
+		.name = "PUD",
+	}, { /* pmd */
+		.bits = gstage_pte_bits,
+		.num = ARRAY_SIZE(gstage_pte_bits),
+		.name = "PMD",
+	}, { /* pte */
+		.bits = gstage_pte_bits,
+		.num = ARRAY_SIZE(gstage_pte_bits),
+		.name = "PTE",
+	},
+};
+
+static void gstage_note_page(struct ptdump_state *pt_st, unsigned long addr,
+			     int level, u64 val)
+{
+	struct ptdump_pg_state *st = container_of(pt_st, struct ptdump_pg_state, ptdump);
+
+	note_page(pt_st, addr, level, val);
+
+	if (level >= 0)
+		st->current_prot = val & gstage_pg_levels[level].mask;
+}
+
+static void gstage_note_page_pte(struct ptdump_state *pt_st, unsigned long addr, pte_t pte)
+{
+	gstage_note_page(pt_st, addr, 4, pte_val(pte));
+}
+
+static void gstage_note_page_pmd(struct ptdump_state *pt_st, unsigned long addr, pmd_t pmd)
+{
+	gstage_note_page(pt_st, addr, 3, pmd_val(pmd));
+}
+
+static void gstage_note_page_pud(struct ptdump_state *pt_st, unsigned long addr, pud_t pud)
+{
+	gstage_note_page(pt_st, addr, 2, pud_val(pud));
+}
+
+static void gstage_note_page_p4d(struct ptdump_state *pt_st, unsigned long addr, p4d_t p4d)
+{
+	gstage_note_page(pt_st, addr, 1, p4d_val(p4d));
+}
+
+static void gstage_note_page_pgd(struct ptdump_state *pt_st, unsigned long addr, pgd_t pgd)
+{
+	gstage_note_page(pt_st, addr, 0, pgd_val(pgd));
+}
+
+static void gstage_note_page_flush(struct ptdump_state *pt_st)
+{
+	pte_t pte_zero = {0};
+
+	gstage_note_page(pt_st, 0, -1, pte_val(pte_zero));
+}
+
+static int gstage_ptdump_show(struct seq_file *m, void *v)
+{
+	struct kvm *kvm = m->private;
+	gpa_t gpa_size = kvm_riscv_gstage_gpa_size(kvm->arch.pgd_levels);
+	struct addr_marker gpa_markers[] = {
+		[GSTAGE_GPA_START_NR] = { 0, "Guest Physical Address Start" },
+		[GSTAGE_GPA_END_NR]   = { gpa_size - 1, "Guest Physical Address End" },
+		[END_OF_GSTAGE_SPACE_NR] = { -1, NULL },
+	};
+	struct ptdump_pg_state st = {
+		.seq = m,
+		.marker = gpa_markers,
+		.level = -1,
+		.pg_level = gstage_pg_levels,
+		.ptdump = {
+			.note_page_pte = gstage_note_page_pte,
+			.note_page_pmd = gstage_note_page_pmd,
+			.note_page_pud = gstage_note_page_pud,
+			.note_page_p4d = gstage_note_page_p4d,
+			.note_page_pgd = gstage_note_page_pgd,
+			.note_page_flush = gstage_note_page_flush,
+			.range = (struct ptdump_range[]) {
+				{0, gpa_size - 1},
+				{0, 0}
+			}
+		}
+	};
+	unsigned int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(gstage_pg_levels); i++) {
+		gstage_pg_levels[i].mask = 0;
+		for (j = 0; j < ARRAY_SIZE(gstage_pte_bits); j++)
+			gstage_pg_levels[i].mask |= gstage_pte_bits[j].mask;
+	}
+
+	if (kvm->arch.pgd_levels < 5)
+		gstage_pg_levels[1].name = "PGD";
+	if (kvm->arch.pgd_levels < 4)
+		gstage_pg_levels[2].name = "PGD";
+	if (kvm->arch.pgd_levels < 3)
+		gstage_pg_levels[3].name = "PGD";
+
+	ptdump_walk_pgd(&st.ptdump, kvm->mm, kvm->arch.pgd);
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(gstage_ptdump);
+
+void kvm_arch_create_vm_debugfs(struct kvm *kvm)
+{
+	debugfs_create_file("gstage_page_tables", 0400,
+			    kvm->debugfs_dentry, kvm, &gstage_ptdump_fops);
+}
-- 
2.34.1