[PATCH v5 3/4] KVM: arm64: Register ptdump with debugfs on guest creation

[Sebastian Ene <sebastianene@google.com>]

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@google.com>
---
 arch/arm64/kvm/Kconfig      | 13 ++++++
 arch/arm64/kvm/Makefile     |  1 +
 arch/arm64/kvm/debug.c      |  7 ++++
 arch/arm64/kvm/kvm_ptdump.h | 20 ++++++++++
 arch/arm64/kvm/ptdump.c     | 79 +++++++++++++++++++++++++++++++++++++
 5 files changed, 120 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 6c3c8ca73e7f..28097dd72174 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -68,4 +68,17 @@ 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..aef52836cd90 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 +344,8 @@ 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)
+{
+	return kvm_ptdump_guest_register(kvm);
+}
diff --git a/arch/arm64/kvm/kvm_ptdump.h b/arch/arm64/kvm/kvm_ptdump.h
new file mode 100644
index 000000000000..a7c00a28481b
--- /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@google.com>
+ */
+
+#ifndef __KVM_PTDUMP_H
+#define __KVM_PTDUMP_H
+
+#include <linux/kvm_host.h>
+#include <asm/ptdump.h>
+
+
+#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
+int kvm_ptdump_guest_register(struct kvm *kvm);
+#else
+static inline int kvm_ptdump_guest_register(struct kvm *kvm) { return 0; }
+#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..a4e984da8aa7
--- /dev/null
+++ b/arch/arm64/kvm/ptdump.c
@@ -0,0 +1,79 @@
+// 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@google.com>
+
+#include <linux/debugfs.h>
+#include <linux/kvm_host.h>
+#include <linux/seq_file.h>
+
+#include <asm/kvm_pkvm.h>
+#include <kvm_ptdump.h>
+
+
+static int kvm_ptdump_guest_open(struct inode *inode, struct file *file);
+static int kvm_ptdump_guest_show(struct seq_file *m, void *);
+
+static const struct file_operations kvm_ptdump_guest_fops = {
+	.open		= kvm_ptdump_guest_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int kvm_ptdump_guest_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, kvm_ptdump_guest_show, inode->i_private);
+}
+
+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 *guest_kvm = m->private;
+	struct kvm_s2_mmu *mmu = &guest_kvm->arch.mmu;
+	struct pg_state parser_state = {0};
+	int ret;
+
+	write_lock(&guest_kvm->mmu_lock);
+	ret = kvm_ptdump_show_common(m, mmu->pgt, &parser_state);
+	write_unlock(&guest_kvm->mmu_lock);
+
+	return ret;
+}
+
+int kvm_ptdump_guest_register(struct kvm *kvm)
+{
+	struct dentry *parent;
+
+	parent = debugfs_create_file("stage2_page_tables", 0400,
+				     kvm->debugfs_dentry, kvm,
+				     &kvm_ptdump_guest_fops);
+	if (IS_ERR(parent))
+		return PTR_ERR(parent);
+	return 0;
+}
-- 
2.43.0.594.gd9cf4e227d-goog