KVM: arm64: Register ptdump with debugfs on guest creation

While arch/*/mem/ptdump handles the kernel pagetable dumping code,
introduce KVM/ptdump to show 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. Introduce the PTDUMP_STAGE2_DEBUGFS config.

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.

[maz: moved function prototypes from kvm_host.h to kvm_mmu.h]

Signed-off-by: Sebastian Ene <sebastianene@google.com>
Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://lore.kernel.org/r/20240909124721.1672199-6-sebastianene@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_mmu.h

@@ -352,5 +352,11 @@ static inline bool kvm_is_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
 	return &kvm->arch.mmu != mmu;
 }
 
+#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
+void kvm_s2_ptdump_create_debugfs(struct kvm *kvm);
+#else
+static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {}
+#endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */
+
 #endif /* __ASSEMBLY__ */
 #endif /* __ARM64_KVM_MMU_H__ */

arch/arm64/kvm/Kconfig

@@ -65,4 +65,21 @@ 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 KVM
+	depends on DEBUG_KERNEL
+	depends on DEBUG_FS
+	depends on GENERIC_PTDUMP
+	select PTDUMP_CORE
+	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

arch/arm64/kvm/Makefile

@@ -24,6 +24,7 @@ kvm-y += arm.o mmu.o mmio.o psci.o hypercalls.o pvtime.o \
 
 kvm-$(CONFIG_HW_PERF_EVENTS)  += pmu-emul.o pmu.o
 kvm-$(CONFIG_ARM64_PTR_AUTH)  += pauth.o
+kvm-$(CONFIG_PTDUMP_STAGE2_DEBUGFS) += ptdump.o
 
 always-y := hyp_constants.h hyp-constants.s
 

arch/arm64/kvm/arm.c

@@ -227,6 +227,7 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 void kvm_arch_create_vm_debugfs(struct kvm *kvm)
 {
 	kvm_sys_regs_create_debugfs(kvm);
+	kvm_s2_ptdump_create_debugfs(kvm);
 }
 
 static void kvm_destroy_mpidr_data(struct kvm *kvm)

arch/arm64/kvm/ptdump.c

@@ -0,0 +1,268 @@
+// 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, 2024
+ * Author: Sebastian Ene <sebastianene@google.com>
+ */
+#include <linux/debugfs.h>
+#include <linux/kvm_host.h>
+#include <linux/seq_file.h>
+
+#include <asm/kvm_mmu.h>
+#include <asm/kvm_pgtable.h>
+#include <asm/ptdump.h>
+
+#define MARKERS_LEN		2
+#define KVM_PGTABLE_MAX_LEVELS	(KVM_PGTABLE_LAST_LEVEL + 1)
+
+struct kvm_ptdump_guest_state {
+	struct kvm		*kvm;
+	struct ptdump_pg_state	parser_state;
+	struct addr_marker	ipa_marker[MARKERS_LEN];
+	struct ptdump_pg_level	level[KVM_PGTABLE_MAX_LEVELS];
+	struct ptdump_range	range[MARKERS_LEN];
+};
+
+static const struct ptdump_prot_bits stage2_pte_bits[] = {
+	{
+		.mask	= PTE_VALID,
+		.val	= PTE_VALID,
+		.set	= " ",
+		.clear	= "F",
+	}, {
+		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | PTE_VALID,
+		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | PTE_VALID,
+		.set	= "R",
+		.clear	= " ",
+	}, {
+		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | PTE_VALID,
+		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | PTE_VALID,
+		.set	= "W",
+		.clear	= " ",
+	}, {
+		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN | PTE_VALID,
+		.val	= PTE_VALID,
+		.set	= " ",
+		.clear	= "X",
+	}, {
+		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_AF | PTE_VALID,
+		.val	= KVM_PTE_LEAF_ATTR_LO_S2_AF | PTE_VALID,
+		.set	= "AF",
+		.clear	= "  ",
+	}, {
+		.mask	= PTE_TABLE_BIT | PTE_VALID,
+		.val	= PTE_VALID,
+		.set	= "BLK",
+		.clear	= "   ",
+	},
+};
+
+static int kvm_ptdump_visitor(const struct kvm_pgtable_visit_ctx *ctx,
+			      enum kvm_pgtable_walk_flags visit)
+{
+	struct ptdump_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_build_levels(struct ptdump_pg_level *level, u32 start_lvl)
+{
+	u32 i;
+	u64 mask;
+
+	if (WARN_ON_ONCE(start_lvl >= KVM_PGTABLE_LAST_LEVEL))
+		return -EINVAL;
+
+	mask = 0;
+	for (i = 0; i < ARRAY_SIZE(stage2_pte_bits); i++)
+		mask |= stage2_pte_bits[i].mask;
+
+	for (i = start_lvl; i < KVM_PGTABLE_MAX_LEVELS; i++) {
+		snprintf(level[i].name, sizeof(level[i].name), "%u", i);
+
+		level[i].num	= ARRAY_SIZE(stage2_pte_bits);
+		level[i].bits	= stage2_pte_bits;
+		level[i].mask	= mask;
+	}
+
+	return 0;
+}
+
+static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm *kvm)
+{
+	struct kvm_ptdump_guest_state *st;
+	struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
+	struct kvm_pgtable *pgtable = mmu->pgt;
+	int ret;
+
+	st = kzalloc(sizeof(struct kvm_ptdump_guest_state), GFP_KERNEL_ACCOUNT);
+	if (!st)
+		return ERR_PTR(-ENOMEM);
+
+	ret = kvm_ptdump_build_levels(&st->level[0], pgtable->start_level);
+	if (ret) {
+		kfree(st);
+		return ERR_PTR(ret);
+	}
+
+	st->ipa_marker[0].name		= "Guest IPA";
+	st->ipa_marker[1].start_address = BIT(pgtable->ia_bits);
+	st->range[0].end		= BIT(pgtable->ia_bits);
+
+	st->kvm				= kvm;
+	st->parser_state = (struct ptdump_pg_state) {
+		.marker		= &st->ipa_marker[0],
+		.level		= -1,
+		.pg_level	= &st->level[0],
+		.ptdump.range	= &st->range[0],
+		.start_address	= 0,
+	};
+
+	return st;
+}
+
+static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
+{
+	int ret;
+	struct kvm_ptdump_guest_state *st = m->private;
+	struct kvm *kvm = st->kvm;
+	struct kvm_s2_mmu *mmu = &kvm->arch.mmu;
+	struct ptdump_pg_state *parser_state = &st->parser_state;
+	struct kvm_pgtable_walker walker = (struct kvm_pgtable_walker) {
+		.cb	= kvm_ptdump_visitor,
+		.arg	= parser_state,
+		.flags	= KVM_PGTABLE_WALK_LEAF,
+	};
+
+	parser_state->seq = m;
+
+	write_lock(&kvm->mmu_lock);
+	ret = kvm_pgtable_walk(mmu->pgt, 0, BIT(mmu->pgt->ia_bits), &walker);
+	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;
+	struct kvm_ptdump_guest_state *st;
+	int ret;
+
+	if (!kvm_get_kvm_safe(kvm))
+		return -ENOENT;
+
+	st = kvm_ptdump_parser_create(kvm);
+	if (IS_ERR(st)) {
+		ret = PTR_ERR(st);
+		goto err_with_kvm_ref;
+	}
+
+	ret = single_open(file, kvm_ptdump_guest_show, st);
+	if (!ret)
+		return 0;
+
+	kfree(st);
+err_with_kvm_ref:
+	kvm_put_kvm(kvm);
+	return ret;
+}
+
+static int kvm_ptdump_guest_close(struct inode *m, struct file *file)
+{
+	struct kvm *kvm = m->i_private;
+	void *st = ((struct seq_file *)file->private_data)->private;
+
+	kfree(st);
+	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,
+};
+
+static int kvm_pgtable_range_show(struct seq_file *m, void *unused)
+{
+	struct kvm_pgtable *pgtable = m->private;
+
+	seq_printf(m, "%2u\n", pgtable->ia_bits);
+	return 0;
+}
+
+static int kvm_pgtable_levels_show(struct seq_file *m, void *unused)
+{
+	struct kvm_pgtable *pgtable = m->private;
+
+	seq_printf(m, "%1d\n", KVM_PGTABLE_MAX_LEVELS - pgtable->start_level);
+	return 0;
+}
+
+static int kvm_pgtable_debugfs_open(struct inode *m, struct file *file,
+				    int (*show)(struct seq_file *, void *))
+{
+	struct kvm *kvm = m->i_private;
+	struct kvm_pgtable *pgtable;
+	int ret;
+
+	if (!kvm_get_kvm_safe(kvm))
+		return -ENOENT;
+
+	pgtable = kvm->arch.mmu.pgt;
+
+	ret = single_open(file, show, pgtable);
+	if (ret < 0)
+		kvm_put_kvm(kvm);
+	return ret;
+}
+
+static int kvm_pgtable_range_open(struct inode *m, struct file *file)
+{
+	return kvm_pgtable_debugfs_open(m, file, kvm_pgtable_range_show);
+}
+
+static int kvm_pgtable_levels_open(struct inode *m, struct file *file)
+{
+	return kvm_pgtable_debugfs_open(m, file, kvm_pgtable_levels_show);
+}
+
+static int kvm_pgtable_debugfs_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_pgtable_range_fops = {
+	.open		= kvm_pgtable_range_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= kvm_pgtable_debugfs_close,
+};
+
+static const struct file_operations kvm_pgtable_levels_fops = {
+	.open		= kvm_pgtable_levels_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= kvm_pgtable_debugfs_close,
+};
+
+void kvm_s2_ptdump_create_debugfs(struct kvm *kvm)
+{
+	debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry,
+			    kvm, &kvm_ptdump_guest_fops);
+	debugfs_create_file("ipa_range", 0400, kvm->debugfs_dentry, kvm,
+			    &kvm_pgtable_range_fops);
+	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
+			    kvm, &kvm_pgtable_levels_fops);
+}