Re: [PATCH v4 02/10] KVM: arm64: Add ptdump registration with debugfs for the stage-2 pagetables

[Sebastian Ene]

On Mon, Dec 18, 2023 at 01:58:52PM +0000, Sebastian Ene wrote:
> While arch/*/mem/ptdump handles the kernel pagetable dumping code,
> introduce KVM/ptdump which deals with the 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.
> 
> This registers a wrapper on top of debugfs_create_file which allows us
> to hook callbacks on the debugfs open/show/close. The callbacks are used
> to prepare the display portion of the pagetable dumping code.
> Guard this functionality under the newly introduced PTDUMP_STAGE2_DEBUGFS.
> 
> Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/Kconfig      | 13 +++++
>  arch/arm64/kvm/Makefile     |  1 +
>  arch/arm64/kvm/arm.c        |  2 +
>  arch/arm64/kvm/kvm_ptdump.h | 18 +++++++
>  arch/arm64/kvm/ptdump.c     | 96 +++++++++++++++++++++++++++++++++++++
>  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 83c1e09be..0014e55e2 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -71,4 +71,17 @@ 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 c0c050e53..190eac175 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/arm.c b/arch/arm64/kvm/arm.c
> index e5f75f1f1..ee8d7cb67 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -40,6 +40,7 @@
>  #include <asm/kvm_pkvm.h>
>  #include <asm/kvm_emulate.h>
>  #include <asm/sections.h>
> +#include <kvm_ptdump.h>
>  
>  #include <kvm/arm_hypercalls.h>
>  #include <kvm/arm_pmu.h>
> @@ -2592,6 +2593,7 @@ static __init int kvm_arm_init(void)
>  	if (err)
>  		goto out_subs;
>  
> +	kvm_ptdump_register_host();
>  	kvm_arm_initialised = true;
>  
>  	return 0;
> diff --git a/arch/arm64/kvm/kvm_ptdump.h b/arch/arm64/kvm/kvm_ptdump.h
> new file mode 100644
> index 000000000..98b595ce8
> --- /dev/null
> +++ b/arch/arm64/kvm/kvm_ptdump.h
> @@ -0,0 +1,18 @@
> +/* 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 <asm/ptdump.h>
> +
> +
> +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS
> +void kvm_ptdump_register_host(void);
> +#else
> +static inline void kvm_ptdump_register_host(void) { }
> +#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 000000000..5816fc632
> --- /dev/null
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -0,0 +1,96 @@
> +// 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_pkvm.h>
> +#include <kvm_ptdump.h>
> +
> +
> +struct kvm_ptdump_register {
> +	void *(*get_ptdump_info)(struct kvm_ptdump_register *reg);
> +	void (*put_ptdump_info)(void *priv);
> +	int (*show_ptdump_info)(struct seq_file *m, void *v);
> +	void *priv;
> +};
> +
> +static int kvm_ptdump_open(struct inode *inode, struct file *file);
> +static int kvm_ptdump_release(struct inode *inode, struct file *file);
> +static int kvm_ptdump_show(struct seq_file *m, void *);
> +
> +static const struct file_operations kvm_ptdump_fops = {
> +	.open		= kvm_ptdump_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= kvm_ptdump_release,
> +};
> +
> +static int kvm_ptdump_open(struct inode *inode, struct file *file)
> +{
> +	struct kvm_ptdump_register *reg = inode->i_private;
> +	void *info = NULL;
> +	int ret;
> +
> +	if (reg->get_ptdump_info) {
> +		info = reg->get_ptdump_info(reg);
> +		if (!info)
> +			return -ENOMEM;
> +	}
> +
> +	if (!reg->show_ptdump_info)
> +		reg->show_ptdump_info = kvm_ptdump_show;
> +
> +	ret = single_open(file, reg->show_ptdump_info, info);
> +	if (ret && reg->put_ptdump_info)
> +		reg->put_ptdump_info(info);
> +
> +	return ret;
> +}
> +
> +static int kvm_ptdump_release(struct inode *inode, struct file *file)
> +{
> +	struct kvm_ptdump_register *reg = inode->i_private;
> +	struct seq_file *seq_file = file->private_data;
> +
> +	if (reg->put_ptdump_info)
> +		reg->put_ptdump_info(seq_file->private);
> +

Call single_release here.

> +	return 0;
> +}
> +
> +static int kvm_ptdump_show(struct seq_file *m, void *)
> +{
> +	return -EINVAL;
> +}
> +
> +static void kvm_ptdump_debugfs_register(struct kvm_ptdump_register *reg,
> +					const char *name, struct dentry *parent)
> +{
> +	debugfs_create_file(name, 0400, parent, reg, &kvm_ptdump_fops);
> +}
> +
> +static struct kvm_ptdump_register host_reg;
> +
> +void kvm_ptdump_register_host(void)
> +{
> +	if (!is_protected_kvm_enabled())
> +		return;
> +
> +	kvm_ptdump_debugfs_register(&host_reg, "host_page_tables",
> +				    kvm_debugfs_dir);
> +}
> +
> +static int __init kvm_host_ptdump_init(void)
> +{
> +	host_reg.priv = (void *)host_s2_pgtable_pages();
> +	return 0;
> +}
> +
> +device_initcall(kvm_host_ptdump_init);
> -- 
> 2.43.0.472.g3155946c3a-goog
>