Message-ID: <ZtGd9UEudn8Z0IlG@google.com>
Date: Fri, 30 Aug 2024 11:24:53 +0100
From: Vincent Donnefort <vdonnefort@...gle.com>
To: Sebastian Ene <sebastianene@...gle.com>
Cc: akpm@...ux-foundation.org, alexghiti@...osinc.com, ankita@...dia.com,
	ardb@...nel.org, catalin.marinas@....com,
	christophe.leroy@...roup.eu, james.morse@....com,
	mark.rutland@....com, maz@...nel.org, oliver.upton@...ux.dev,
	rananta@...gle.com, ryan.roberts@....com, shahuang@...hat.com,
	suzuki.poulose@....com, will@...nel.org, yuzenghui@...wei.com,
	kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v9 4/5] KVM: arm64: Register ptdump with debugfs on guest
 creation

Hi Seb,

Thanks for the respin.

On Tue, Aug 27, 2024 at 08:45:47AM +0000, Sebastian Ene wrote:
> 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.
> 
> 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@...gle.com>

I only have some nits, otherwise:

Reviewed-by: Vincent Donnefort <vdonnefort@...gle.com>

> ---
>  arch/arm64/include/asm/kvm_host.h |   6 +
>  arch/arm64/kvm/Makefile           |   1 +
>  arch/arm64/kvm/arm.c              |   1 +
>  arch/arm64/kvm/ptdump.c           | 247 ++++++++++++++++++++++++++++++
>  4 files changed, 255 insertions(+)
>  create mode 100644 arch/arm64/kvm/ptdump.c
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index a33f5996ca9f..4acd589f086b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1473,4 +1473,10 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
>  		(pa + pi + pa3) == 1;					\
>  	})
>  
> +#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 /* __ARM64_KVM_HOST_H__ */
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 86a629aaf0a1..e4233b323a73 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -27,6 +27,7 @@ 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
>  
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9bef7638342e..b9fd928d3477 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -228,6 +228,7 @@ 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)
> diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> new file mode 100644
> index 000000000000..e72a928d4445
> --- /dev/null
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -0,0 +1,247 @@
> +// 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@...gle.com>
> + */
> +#include <linux/debugfs.h>
> +#include <linux/kvm_host.h>
> +#include <linux/seq_file.h>
> +
> +#include <asm/kvm_pgtable.h>
> +#include <asm/kvm_host.h>

nit: I believe you wanted to follow the alphabetical order, if that is the case,
kvm_host.h then kvm_pgtable.h

> +#include <asm/ptdump.h>
> +
> +

nit: don't think double empty are a rule, I would remove it.

> +#define MARKERS_LEN		(2)

nit: The brackets are not necessary for MARKERS_LEN.

> +#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",

This is effectively never used because an invalid PTE is 0 and note_page() won't
print it. This probably can be removed?

> +	}, {
> +		.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), "%d", i);

%u, i being unsigned.

> +
> +		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 free_with_kvm_ref;
> +	}
> +
> +	ret = single_open(file, kvm_ptdump_guest_show, st);
> +	if (!ret)
> +		return 0;
> +
> +	kfree(st);
> +free_with_kvm_ref:

nit: I believe kfree understands IS_ERR() so you could have a simple "err:"
label covering all the error path.

> +	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_debugfs_show(struct seq_file *m, void *unused)
> +{
> +	const struct file *file = m->file;
> +	struct kvm_pgtable *pgtable = m->private;
> +
> +	if (!strcmp(file_dentry(file)->d_iname, "ipa_range"))
> +		seq_printf(m, "%2u\n", pgtable->ia_bits);
> +	else if (!strcmp(file_dentry(file)->d_iname, "stage2_levels"))
> +		seq_printf(m, "%1d\n", KVM_PGTABLE_LAST_LEVEL - pgtable->start_level + 1);

nit: KVM_PGTABLE_MAX_LEVELS - pgtable->start_level ?

> +	return 0;
> +}
> +
> +static int kvm_pgtable_debugfs_open(struct inode *m, struct file *file)
> +{
> +	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, kvm_pgtable_debugfs_show, pgtable);
> +	if (ret < 0)
> +		kvm_put_kvm(kvm);
> +	return ret;
> +}
> +
> +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_debugfs_fops = {
> +	.open		= kvm_pgtable_debugfs_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_debugfs_fops);
> +	debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry,
> +			    kvm, &kvm_pgtable_debugfs_fops);
> +}
> -- 
> 2.46.0.295.g3b9ea8a38a-goog
> 

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