[PATCH v2 3/3] KVM: riscv: Register ptdump with debugfs on guest creation
Dylan.Wu
fredwudi0305 at gmail.com
Mon Jul 27 05:30:13 PDT 2026
Add a new RISC-V KVM specific ptdump implementation that dumps the
guest stage-2 (gstage) pagetables via debugfs. The code reuses the
common ptdump data structures and helpers from asm/ptdump.h, and
exposes a "gstage_page_tables" file in each guest VM's debugfs
directory (kvm->debugfs_dentry).
The gstage uses its own set of pg_level and prot_bits arrays (a
simplified set of V/R/W/X/D/A/G/U bits), and plugs these into the
generic ptdump_walk_pgd() walker just like the host kernel ptdump.
The kvm_arch_create_vm_debugfs() hook (overriding the weak default)
is used to register the debugfs file automatically on each VM
creation.
Assisted-by: YuanSheng: deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan at iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan at iscas.ac.cn>
Signed-off-by: Dylan.Wu <fredwudi0305 at gmail.com>
---
arch/riscv/kvm/Kconfig | 15 +++
arch/riscv/kvm/Makefile | 1 +
arch/riscv/kvm/ptdump.c | 276 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 292 insertions(+)
create mode 100644 arch/riscv/kvm/ptdump.c
diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
index ec2cee0a3..9413110a4 100644
--- a/arch/riscv/kvm/Kconfig
+++ b/arch/riscv/kvm/Kconfig
@@ -37,4 +37,19 @@ config KVM
If unsure, say N.
+config PTDUMP_GSTAGE_DEBUGFS
+ bool "Present the gstage pagetables to debugfs"
+ depends on KVM
+ depends on DEBUG_KERNEL
+ depends on DEBUG_FS
+ depends on PTDUMP_DEBUGFS
+ default n
+ help
+ Say Y here if you want to show the RISC-V KVM gstage guest page tables
+ layout in a debugfs file. This information is primarily useful for
+ architecture-specific kernel developers and KVM maintainers to
+ investigate memory mapping and permission issues. It is probably
+ not a good idea to enable this feature in a production kernel.
+ If in doubt, 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..83a92969b
--- /dev/null
+++ b/arch/riscv/kvm/ptdump.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 SiFive
+ * Debug helper to dump the KVM gstage page tables.
+ */
+
+#include <linux/init.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/string.h>
+#include <linux/ptdump.h>
+#include <linux/kvm_host.h>
+
+#include <linux/pgtable.h>
+#include <asm/ptdump.h>
+#include <asm/kvm_gstage.h>
+#include <asm/kvm_mmu.h>
+
+#define pt_dump_seq_printf(m, fmt, args...) \
+({ \
+ if (m) \
+ seq_printf(m, fmt, ##args); \
+})
+
+#define pt_dump_seq_puts(m, fmt) \
+({ \
+ if (m) \
+ seq_puts(m, fmt); \
+})
+
+/* Guest physical address markers (simplified for gstage) */
+enum gstage_address_markers_idx {
+ GSTAGE_GPA_START_NR,
+ GSTAGE_GPA_END_NR,
+ END_OF_GSTAGE_SPACE_NR
+};
+
+/* G-stage PTE bits */
+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 = (CONFIG_PGTABLE_LEVELS > 4) ? "P4D" : "PGD",
+ }, { /* pud */
+ .bits = gstage_pte_bits,
+ .num = ARRAY_SIZE(gstage_pte_bits),
+ .name = (CONFIG_PGTABLE_LEVELS > 3) ? "PUD" : "PGD",
+ }, { /* pmd */
+ .bits = gstage_pte_bits,
+ .num = ARRAY_SIZE(gstage_pte_bits),
+ .name = (CONFIG_PGTABLE_LEVELS > 2) ? "PMD" : "PGD",
+ }, { /* pte */
+ .bits = gstage_pte_bits,
+ .num = ARRAY_SIZE(gstage_pte_bits),
+ .name = "PTE",
+ },
+};
+
+static void gstage_dump_prot(struct ptdump_pg_state *st)
+{
+ const struct ptdump_pg_level *lvl = &st->pg_level[st->level];
+ const struct ptdump_prot_bits *bits = lvl->bits;
+ unsigned int i;
+
+ for (i = 0; i < lvl->num; i++) {
+ char s[7];
+ unsigned long val;
+
+ val = st->current_prot & bits[i].mask;
+ if (val)
+ strscpy(s, bits[i].set);
+ else
+ strscpy(s, bits[i].clear);
+
+ pt_dump_seq_printf(st->seq, " %s", s);
+ }
+}
+
+#ifdef CONFIG_64BIT
+#define GSTAGE_ADDR_FORMAT "0x%016lx"
+#else
+#define GSTAGE_ADDR_FORMAT "0x%08lx"
+#endif
+static void gstage_dump_addr(struct ptdump_pg_state *st, unsigned long addr)
+{
+ static const char units[] = "KMGTPE";
+ const char *unit = units;
+ unsigned long delta;
+
+ pt_dump_seq_printf(st->seq, GSTAGE_ADDR_FORMAT "-" GSTAGE_ADDR_FORMAT " ",
+ st->start_address, addr);
+
+ pt_dump_seq_printf(st->seq, " " GSTAGE_ADDR_FORMAT " ", st->start_pa);
+ delta = (addr - st->start_address) >> 10;
+
+ while (!(delta & 1023) && unit[1]) {
+ delta >>= 10;
+ unit++;
+ }
+
+ pt_dump_seq_printf(st->seq, "%9lu%c %s", delta, *unit,
+ st->pg_level[st->level].name);
+}
+
+static void gstage_note_page_gpa_prot(struct ptdump_pg_state *st, unsigned long addr)
+{
+ if (st->current_prot) {
+ gstage_dump_addr(st, addr);
+ gstage_dump_prot(st);
+ pt_dump_seq_puts(st->seq, "\n");
+ }
+}
+
+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);
+ u64 pa = PFN_PHYS(pte_pfn(__pte(val)));
+ u64 prot = 0;
+
+ if (level >= 0)
+ prot = val & st->pg_level[level].mask;
+
+ if (st->level == -1) {
+ st->level = level;
+ st->current_prot = prot;
+ st->start_address = addr;
+ st->start_pa = pa;
+ st->last_pa = pa;
+ pt_dump_seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+ } else if (prot != st->current_prot ||
+ level != st->level || addr >= st->marker[1].start_address) {
+ gstage_note_page_gpa_prot(st, addr);
+
+ while (addr >= st->marker[1].start_address) {
+ st->marker++;
+ pt_dump_seq_printf(st->seq, "---[ %s ]---\n",
+ st->marker->name);
+ }
+
+ st->start_address = addr;
+ st->start_pa = pa;
+ st->last_pa = pa;
+ st->current_prot = prot;
+ st->level = level;
+ } else {
+ st->last_pa = pa;
+ }
+}
+
+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
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