Re: [PATCH v9 4/5] KVM: arm64: Register ptdump with debugfs on guest creation

[Sebastian Ene <sebastianene@google.com>]

On Fri, Aug 30, 2024 at 11:24:53AM +0100, Vincent Donnefort wrote:
> 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@google.com>
> 
> I only have some nits, otherwise:

Hello Vincent,

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

Thanks for giving me consistent feedback on the series. I will
incorporate your latest suggestions in my patch series and add the tag.

> > ---
> >  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@google.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.
> 

Ack.

> > +#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?
> 

Please see my previous reply to this. I would keep it around as it
should print out non-zero invalid PTEs.

> > +	}, {
> > +		.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.

Ack.

> 
> > +
> > +		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 ?

Yes, we can use this one.

> 
> > +	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
> >