[PATCH 2/2] KVM: riscv: Register ptdump with debugfs on guest creation
Dylan.Wu
fredwudi0305 at gmail.com
Wed Jul 1 01:50:30 PDT 2026
Introduce KVM ptdump to show the guest gstage pagetables. This registers
a 'gstage_page_tables' file under the guest debugfs directory.
Userspace can now inspect the gstage layout and permissions, which
is useful for architectural debugging and memory management audits.
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/include/asm/kvm_host.h | 6 +
arch/riscv/kvm/Kconfig | 15 +++
arch/riscv/kvm/Makefile | 1 +
arch/riscv/kvm/ptdump.c | 178 ++++++++++++++++++++++++++++++
arch/riscv/kvm/vm.c | 5 +
5 files changed, 205 insertions(+)
create mode 100644 arch/riscv/kvm/ptdump.c
diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
index 60017ceec..04129c5f8 100644
--- a/arch/riscv/include/asm/kvm_host.h
+++ b/arch/riscv/include/asm/kvm_host.h
@@ -322,4 +322,10 @@ void kvm_riscv_vcpu_record_steal_time(struct kvm_vcpu *vcpu);
/* Flags representing implementation specific details */
DECLARE_STATIC_KEY_FALSE(kvm_riscv_vsstage_tlb_no_gpa);
+#ifdef CONFIG_PTDUMP_GSTAGE_DEBUGFS
+void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
+#else
+static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
+#endif
+
#endif /* __RISCV_KVM_HOST_H__ */
diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
index ec2cee0a3..0ceb4a452 100644
--- a/arch/riscv/kvm/Kconfig
+++ b/arch/riscv/kvm/Kconfig
@@ -38,3 +38,18 @@ config KVM
If unsure, say N.
endif # VIRTUALIZATION
+
+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.
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index 296c2ba05..0170c8c3b 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -42,3 +42,4 @@ kvm-y += vcpu_timer.o
kvm-y += vcpu_vector.o
kvm-y += vm.o
kvm-y += vmid.o
+kvm-$(CONFIG_PTDUMP_GSTAGE_DEBUGFS) += ptdump.o
diff --git a/arch/riscv/kvm/ptdump.c b/arch/riscv/kvm/ptdump.c
new file mode 100644
index 000000000..972d45d69
--- /dev/null
+++ b/arch/riscv/kvm/ptdump.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Debug helper used to dump the gstage pagetables of the system.
+ */
+#include <linux/debugfs.h>
+#include <linux/kvm_host.h>
+#include <linux/seq_file.h>
+#include <linux/mm.h>
+#include <asm/ptdump.h>
+#include <asm/pgtable.h>
+
+static const struct ptdump_prot_bits gstage_pte_bits[] = {
+ {
+ .mask = _PAGE_SOFT,
+ .set = "RSW(%d)",
+ .clear = " .. ",
+ }, {
+ .mask = _PAGE_DIRTY,
+ .set = "D",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_ACCESSED,
+ .set = "A",
+ .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[] = {
+ { .name = "PGD" },
+ { .name = "P4D" },
+ { .name = "PUD" },
+ { .name = "PMD" },
+ { .name = "PTE" },
+};
+
+struct kvm_ptdump_state {
+ struct kvm *kvm;
+ struct ptdump_pg_state parser_state;
+ struct addr_marker marker[2];
+ struct ptdump_range range[2];
+};
+
+static void kvm_ptdump_walk_level(struct ptdump_state *pt_st,
+ unsigned long *tbl, int level,
+ unsigned long start_addr)
+{
+ unsigned long addr = start_addr;
+ unsigned long next, virt_addr;
+ int i;
+ unsigned long step = 1UL << (PAGE_SHIFT + (4 - level) * 9);
+
+ for (i = 0; i < PTRS_PER_PTE; i++, addr += step) {
+ unsigned long val = tbl[i];
+
+ next = addr + step;
+
+ if (level == 4 || (val & _PAGE_LEAF) || !(val & _PAGE_PRESENT)) {
+ note_page(pt_st, addr, level, val);
+ } else {
+ unsigned long pa = (val >> _PAGE_PFN_SHIFT) << PAGE_SHIFT;
+
+ virt_addr = (unsigned long)phys_to_virt(pa);
+
+ kvm_ptdump_walk_level(pt_st, (unsigned long *)virt_addr,
+ level + 1, addr);
+ }
+ }
+}
+
+static int kvm_ptdump_visitor(struct seq_file *m, void *v)
+{
+ struct kvm_ptdump_state *st = m->private;
+ struct kvm *kvm = st->kvm;
+ unsigned long *pgd = (unsigned long *)kvm->arch.pgd;
+ int start_level = 5 - kvm->arch.pgd_levels;
+ int i, j;
+
+ st->parser_state.level = -1;
+ st->parser_state.start_address = 0;
+ st->parser_state.seq = m;
+
+ for (i = 0; i < ARRAY_SIZE(gstage_pg_levels); i++) {
+ gstage_pg_levels[i].bits = gstage_pte_bits;
+ gstage_pg_levels[i].num = ARRAY_SIZE(gstage_pte_bits);
+ 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;
+ }
+
+ read_lock(&kvm->mmu_lock);
+ if (pgd) {
+ kvm_ptdump_walk_level(&st->parser_state.ptdump, pgd,
+ start_level, 0);
+ }
+ read_unlock(&kvm->mmu_lock);
+
+ note_page(&st->parser_state.ptdump, 0, -1, 0);
+ return 0;
+}
+
+static int kvm_ptdump_open(struct inode *inode, struct file *file)
+{
+ struct kvm *kvm = inode->i_private;
+ struct kvm_ptdump_state *st;
+ int ret;
+
+ if (!kvm_get_kvm_safe(kvm))
+ return -ENOENT;
+
+ st = kzalloc(sizeof(*st), GFP_KERNEL);
+ if (!st) {
+ kvm_put_kvm(kvm);
+ return -ENOMEM;
+ }
+
+ st->kvm = kvm;
+ st->marker[0].name = "Guest IPA";
+ st->marker[0].start_address = 0;
+ st->marker[1].start_address = -1UL;
+ st->range[0].start = 0;
+ st->range[0].end = -1UL;
+
+ st->parser_state.marker = st->marker;
+ st->parser_state.pg_level = gstage_pg_levels;
+ st->parser_state.ptdump.range = st->range;
+
+ ret = single_open(file, kvm_ptdump_visitor, st);
+ if (ret) {
+ kfree(st);
+ kvm_put_kvm(kvm);
+ }
+ return ret;
+}
+
+static int kvm_ptdump_release(struct inode *inode, struct file *file)
+{
+ struct seq_file *seq = file->private_data;
+ struct kvm_ptdump_state *st = seq->private;
+ struct kvm *kvm = st->kvm;
+
+ kfree(st);
+ kvm_put_kvm(kvm);
+ return single_release(inode, file);
+}
+
+static const struct file_operations kvm_gstage_fops = {
+ .owner = THIS_MODULE,
+ .open = kvm_ptdump_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = kvm_ptdump_release,
+};
+
+void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
+{
+ debugfs_create_file("gstage_page_tables", 0400, kvm->debugfs_dentry, kvm,
+ &kvm_gstage_fops);
+}
diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
index a9f083fee..464ad2eaf 100644
--- a/arch/riscv/kvm/vm.c
+++ b/arch/riscv/kvm/vm.c
@@ -269,3 +269,8 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
{
return -EINVAL;
}
+
+void kvm_arch_create_vm_debugfs(struct kvm *kvm)
+{
+ kvm_s2_ptdump_create_debugfs(kvm);
+}
--
2.34.1
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