[PATCH v6 4/6] KVM: arm64: Register ptdump with debugfs on guest creation
From: Sebastian Ene
Date: Tue Feb 20 2024 - 10:12:58 EST
While arch/*/mem/ptdump handles the kernel pagetable dumping code,
introduce KVM/ptdump which shows the guest stage-2 pagetables. The
separation is necessary because most of the definitions from the
stage-2 pagetable reside in the KVM path and we will be invoking
functionality **specific** to KVM.
When a guest is created, register a new file entry under the guest
debugfs dir which allows userspace to show the contents of the guest
stage-2 pagetables when accessed.
Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
---
arch/arm64/kvm/Kconfig | 13 ++++++
arch/arm64/kvm/Makefile | 1 +
arch/arm64/kvm/debug.c | 8 ++++
arch/arm64/kvm/kvm_ptdump.h | 20 +++++++++
arch/arm64/kvm/ptdump.c | 88 +++++++++++++++++++++++++++++++++++++
5 files changed, 130 insertions(+)
create mode 100644 arch/arm64/kvm/kvm_ptdump.h
create mode 100644 arch/arm64/kvm/ptdump.c
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 27ca89b628a0..83ca07d16cf4 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -67,4 +67,17 @@ config PROTECTED_NVHE_STACKTRACE
If unsure, or not using protected nVHE (pKVM), say N.
+config PTDUMP_STAGE2_DEBUGFS
+ bool "Present the stage-2 pagetables to debugfs"
+ depends on PTDUMP_DEBUGFS && KVM
+ default n
+ help
+ Say Y here if you want to show the stage-2 kernel pagetables
+ layout in a debugfs file. This information is only useful for kernel developers
+ who are working in architecture specific areas of the kernel.
+ 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/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index c0c050e53157..190eac17538c 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -23,6 +23,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
vgic/vgic-its.o vgic/vgic-debug.o
kvm-$(CONFIG_HW_PERF_EVENTS) += pmu-emul.o pmu.o
+kvm-$(CONFIG_PTDUMP_STAGE2_DEBUGFS) += ptdump.o
always-y := hyp_constants.h hyp-constants.s
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 8725291cb00a..ff97af2c0513 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -14,6 +14,8 @@
#include <asm/kvm_arm.h>
#include <asm/kvm_emulate.h>
+#include <kvm_ptdump.h>
+
#include "trace.h"
/* These are the bits of MDSCR_EL1 we may manipulate */
@@ -342,3 +344,9 @@ void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);
vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
}
+
+int kvm_arch_create_vm_debugfs(struct kvm *kvm)
+{
+ kvm_ptdump_guest_register(kvm);
+ return 0;
+}
diff --git a/arch/arm64/kvm/kvm_ptdump.h b/arch/arm64/kvm/kvm_ptdump.h
new file mode 100644
index 000000000000..5e8a655605f1
--- /dev/null
+++ b/arch/arm64/kvm/kvm_ptdump.h
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) Google, 2023
+ * Author: Sebastian Ene <sebastianene@xxxxxxxxxx>
+ */
+
+#ifndef __KVM_PTDUMP_H
+#define __KVM_PTDUMP_H
+
+#include <linux/kvm_host.h>
+#include <asm/ptdump.h>
+
+
+#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
+void kvm_ptdump_guest_register(struct kvm *kvm);
+#else
+static inline void kvm_ptdump_guest_register(struct kvm *kvm) {}
+#endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
+
+#endif /* __KVM_PTDUMP_H */
diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
new file mode 100644
index 000000000000..9b04c24bb9be
--- /dev/null
+++ b/arch/arm64/kvm/ptdump.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Debug helper used to dump the stage-2 pagetables of the system and their
+ * associated permissions.
+ *
+ * Copyright (C) Google, 2023
+ * Author: Sebastian Ene <sebastianene@xxxxxxxxxx>
+ */
+#include <linux/debugfs.h>
+#include <linux/kvm_host.h>
+#include <linux/seq_file.h>
+
+#include <asm/kvm_pgtable.h>
+#include <kvm_ptdump.h>
+
+
+static int kvm_ptdump_visitor(const struct kvm_pgtable_visit_ctx *ctx,
+ enum kvm_pgtable_walk_flags visit)
+{
+ struct pg_state *st = ctx->arg;
+ struct ptdump_state *pt_st = &st->ptdump;
+
+ note_page(pt_st, ctx->addr, ctx->level, ctx->old);
+ return 0;
+}
+
+static int kvm_ptdump_show_common(struct seq_file *m,
+ struct kvm_pgtable *pgtable,
+ struct pg_state *parser_state)
+{
+ struct kvm_pgtable_walker walker = (struct kvm_pgtable_walker) {
+ .cb = kvm_ptdump_visitor,
+ .arg = parser_state,
+ .flags = KVM_PGTABLE_WALK_LEAF,
+ };
+
+ return kvm_pgtable_walk(pgtable, 0, BIT(pgtable->ia_bits), &walker);
+}
+
+static int kvm_ptdump_guest_show(struct seq_file *m, void *)
+{
+ struct kvm *kvm = m->private;
+ struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
+ struct pg_state parser_state = {0};
+ int ret;
+
+ write_lock(&kvm->mmu_lock);
+ ret = kvm_ptdump_show_common(m, mmu->pgt, &parser_state);
+ write_unlock(&kvm->mmu_lock);
+
+ return ret;
+}
+
+static int kvm_ptdump_guest_open(struct inode *m, struct file *file)
+{
+ struct kvm *kvm = m->i_private;
+ int ret;
+
+ if (!kvm_get_kvm_safe(kvm))
+ return -ENOENT;
+
+ ret = single_open(file, kvm_ptdump_guest_show, m->i_private);
+ if (ret < 0)
+ kvm_put_kvm(kvm);
+
+ return ret;
+}
+
+static int kvm_ptdump_guest_close(struct inode *m, struct file *file)
+{
+ struct kvm *kvm = m->i_private;
+
+ kvm_put_kvm(kvm);
+ return single_release(m, file);
+}
+
+static const struct file_operations kvm_ptdump_guest_fops = {
+ .open = kvm_ptdump_guest_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = kvm_ptdump_guest_close,
+};
+
+void kvm_ptdump_guest_register(struct kvm *kvm)
+{
+ debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
+ kvm, &kvm_ptdump_guest_fops);
+}
--
2.44.0.rc0.258.g7320e95886-goog