Re: [PATCH 03/17] vdso: Add generic time data storage

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 16/12/2024 à 15:09, Thomas Weißschuh a écrit :
> Historically each architecture defined their own way to store the vDSO
> data page. Add a generic mechanism to provide storage for that page.
> 
> Furthermore this generic storage will be extended to also provide
> uniform storage for *non*-time-related data, like the random state or
> architecture-specific data. These will have their own pages and data
> structures, so rename 'vdso_data' into 'vdso_time_data' to make that
> split clear from the name.
> 
> Also introduce a new consistent naming scheme for the symbols related to
> the vDSO, which makes it clear if the symbol is accessible from
> userspace or kernel space and the type of data behind the symbol.
> 
> The generic fault handler contains an optimization to prefault the vvar
> page when the timens page is accessed. This was lifted from s390 and x86.
> 
> Co-developed-by: Nam Cao <namcao@linutronix.de>
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> ---
>   MAINTAINERS                    |  1 +
>   include/linux/time_namespace.h |  1 +
>   include/linux/vdso_datastore.h | 10 +++++
>   include/vdso/datapage.h        | 69 +++++++++++++++++++++++++----
>   lib/Kconfig                    |  1 +
>   lib/Makefile                   |  2 +
>   lib/vdso_kernel/Kconfig        |  7 +++
>   lib/vdso_kernel/Makefile       |  3 ++
>   lib/vdso_kernel/datastore.c    | 99 ++++++++++++++++++++++++++++++++++++++++++

There is only one single file, namely datastore.c. You don't need a new 
directory for that, I should go in lib/vdso/


>   9 files changed, 185 insertions(+), 8 deletions(-)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1e930c7a58b13d8bbe6bf133ba7b36aa24c2b5e0..9d947e1e90ff3c6060e56f3b7eaa28cd60d6191c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9677,6 +9677,7 @@ F:	include/asm-generic/vdso/vsyscall.h
>   F:	include/vdso/
>   F:	kernel/time/vsyscall.c
>   F:	lib/vdso/
> +F:	lib/vdso_kernel/

New dir not needed

>   
>   GENWQE (IBM Generic Workqueue Card)
>   M:	Frank Haverkamp <haver@linux.ibm.com>
> diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
> index 876e31b4461d0ee01fe2bd3d136acdea2611789f..4b81db223f5450218dfaf553b24195be9ba97c08 100644
> --- a/include/linux/time_namespace.h
> +++ b/include/linux/time_namespace.h
> @@ -8,6 +8,7 @@
>   #include <linux/ns_common.h>
>   #include <linux/err.h>
>   #include <linux/time64.h>
> +#include <vdso/datapage.h>
>   
>   struct user_namespace;
>   extern struct user_namespace init_user_ns;
> diff --git a/include/linux/vdso_datastore.h b/include/linux/vdso_datastore.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..a91fa24b06e09321fdff8c2c7bdfbc1b206db574
> --- /dev/null
> +++ b/include/linux/vdso_datastore.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_VDSO_DATASTORE_H
> +#define _LINUX_VDSO_DATASTORE_H
> +
> +#include <linux/mm_types.h>
> +
> +extern const struct vm_special_mapping vdso_vvar_mapping;
> +struct vm_area_struct *vdso_install_vvar_mapping(struct mm_struct *mm, unsigned long addr);
> +
> +#endif /* _LINUX_VDSO_DATASTORE_H */
> diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
> index d967baa0cd0c65784e38dc4fcd7b9e8273923947..69af424413db1f265607d0f1bdbf88550548c5ba 100644
> --- a/include/vdso/datapage.h
> +++ b/include/vdso/datapage.h
> @@ -45,11 +45,11 @@ struct arch_vdso_time_data {};
>    *
>    * There is one vdso_timestamp object in vvar for each vDSO-accelerated
>    * clock_id. For high-resolution clocks, this encodes the time
> - * corresponding to vdso_data.cycle_last. For coarse clocks this encodes
> + * corresponding to vdso_time_data.cycle_last. For coarse clocks this encodes
>    * the actual time.
>    *
>    * To be noticed that for highres clocks nsec is left-shifted by
> - * vdso_data.cs[x].shift.
> + * vdso_time_data[x].shift.
>    */
>   struct vdso_timestamp {
>   	u64	sec;
> @@ -57,7 +57,7 @@ struct vdso_timestamp {
>   };
>   
>   /**
> - * struct vdso_data - vdso datapage representation
> + * struct vdso_time_data - vdso datapage representation
>    * @seq:		timebase sequence counter
>    * @clock_mode:		clock mode
>    * @cycle_last:		timebase at clocksource init
> @@ -74,7 +74,7 @@ struct vdso_timestamp {
>    * @arch_data:		architecture specific data (optional, defaults
>    *			to an empty struct)
>    *
> - * vdso_data will be accessed by 64 bit and compat code at the same time
> + * vdso_time_data will be accessed by 64 bit and compat code at the same time
>    * so we should be careful before modifying this structure.
>    *
>    * The ordering of the struct members is optimized to have fast access to the
> @@ -92,7 +92,7 @@ struct vdso_timestamp {
>    * For clocks which are not affected by time namespace adjustment the
>    * offset must be zero.
>    */
> -struct vdso_data {
> +struct vdso_time_data {
>   	u32			seq;
>   
>   	s32			clock_mode;
> @@ -117,6 +117,8 @@ struct vdso_data {
>   	struct arch_vdso_time_data arch_data;
>   };
>   
> +#define vdso_data vdso_time_data
> +
>   /**
>    * struct vdso_rng_data - vdso RNG state information
>    * @generation:	counter representing the number of RNG reseeds
> @@ -136,18 +138,55 @@ struct vdso_rng_data {
>    * With the hidden visibility, the compiler simply generates a PC-relative
>    * relocation, and this is what we need.
>    */
> -extern struct vdso_data _vdso_data[CS_BASES] __attribute__((visibility("hidden")));
> -extern struct vdso_data _timens_data[CS_BASES] __attribute__((visibility("hidden")));
> +#ifndef CONFIG_GENERIC_VDSO_DATA_STORE
> +extern struct vdso_time_data _vdso_data[CS_BASES] __attribute__((visibility("hidden")));
> +extern struct vdso_time_data _timens_data[CS_BASES] __attribute__((visibility("hidden")));
>   extern struct vdso_rng_data _vdso_rng_data __attribute__((visibility("hidden")));
> +#else
> +extern const struct vdso_time_data vdso_u_time_data[CS_BASES] __attribute__((visibility("hidden")));
> +extern const struct vdso_time_data vdso_u_timens_data[CS_BASES] __attribute__((visibility("hidden")));
> +
> +extern struct vdso_time_data *vdso_k_time_data;
> +#endif
>   
>   /**
>    * union vdso_data_store - Generic vDSO data page
>    */
>   union vdso_data_store {
> -	struct vdso_data	data[CS_BASES];
> +	struct vdso_time_data	data[CS_BASES];
>   	u8			page[1U << CONFIG_PAGE_SHIFT];
>   };
>   
> +#ifdef CONFIG_GENERIC_VDSO_DATA_STORE
> +
> +enum vdso_pages {
> +	VDSO_TIME_PAGE_OFFSET,
> +	VDSO_TIMENS_PAGE_OFFSET,
> +	VDSO_NR_PAGES
> +};

Naming that VDSO_ is confusing. Most macros called VDSO_ are related to 
the VDSO Code. VDSO data related macros should be prefixed with VVAR_

> +
> +static __always_inline struct vdso_time_data *__arch_get_vdso_k_time_data(void)
> +{
> +	return vdso_k_time_data;
> +}
> +#define __arch_get_k_vdso_data __arch_get_vdso_k_time_data
> +
> +static __always_inline const struct vdso_time_data *__arch_get_vdso_u_time_data(void)
> +{
> +	return vdso_u_time_data;
> +}
> +#define __arch_get_vdso_data __arch_get_vdso_u_time_data
> +
> +#ifdef CONFIG_TIME_NS
> +static __always_inline const struct vdso_time_data *__arch_get_vdso_u_timens_data(void)
> +{
> +	return vdso_u_timens_data;
> +}
> +#define __arch_get_timens_vdso_data(vd) __arch_get_vdso_u_timens_data()
> +#endif /* CONFIG_TIME_NS */
> +
> +#endif /* CONFIG_GENERIC_VDSO_DATA_STORE */
> +
>   /*
>    * The generic vDSO implementation requires that gettimeofday.h
>    * provides:
> @@ -164,6 +203,20 @@ union vdso_data_store {
>   #include <asm/vdso/gettimeofday.h>
>   #endif /* ENABLE_COMPAT_VDSO */
>   
> +#else /* !__ASSEMBLY__ */
> +
> +#ifdef CONFIG_TIME_NS
> +#define __vdso_u_timens_data	PROVIDE(vdso_u_timens_data = vdso_u_data + PAGE_SIZE);
> +#else
> +#define __vdso_u_timens_data
> +#endif
> +
> +#define VDSO_VVAR_SYMS						\
> +	PROVIDE(vdso_u_data = . - __VDSO_PAGES * PAGE_SIZE);	\
> +	PROVIDE(vdso_u_time_data = vdso_u_data);		\
> +	__vdso_u_timens_data					\
> +
> +
>   #endif /* !__ASSEMBLY__ */
>   
>   #endif /* __VDSO_DATAPAGE_H */
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 5a318f753b2f44cb0a7905cc0092e81c133bc112..7d59b2c10ce5ffab03378ead254d9f9017a4482f 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -659,6 +659,7 @@ config UCS2_STRING
>   # generic vdso
>   #
>   source "lib/vdso/Kconfig"
> +source "lib/vdso_kernel/Kconfig"
>   
>   source "lib/fonts/Kconfig"
>   
> diff --git a/lib/Makefile b/lib/Makefile
> index a8155c972f02856fcc61ee949ddda436cfe211ff..aeedeea86b26cee50d7ced18f9b77b3c51201930 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -401,3 +401,5 @@ obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
>   obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o
>   
>   subdir-$(CONFIG_FORTIFY_SOURCE) += test_fortify
> +
> +obj-y += vdso_kernel/

No need for a new directory

> diff --git a/lib/vdso_kernel/Kconfig b/lib/vdso_kernel/Kconfig
> new file mode 100644
> index 0000000000000000000000000000000000000000..0c7ade9b3ece67c0c0ca892544b9e29e53c860c4
> --- /dev/null
> +++ b/lib/vdso_kernel/Kconfig
> @@ -0,0 +1,7 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +config GENERIC_VDSO_DATA_STORE
> +	bool
> +	depends on HAVE_GENERIC_VDSO
> +	help
> +	  Selected by architectures that use the generic vDSO data store.
> diff --git a/lib/vdso_kernel/Makefile b/lib/vdso_kernel/Makefile
> new file mode 100644
> index 0000000000000000000000000000000000000000..4826e49f9edbdb48506b50957584ed89bde5f37f
> --- /dev/null
> +++ b/lib/vdso_kernel/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_GENERIC_VDSO_DATA_STORE) += datastore.o
> diff --git a/lib/vdso_kernel/datastore.c b/lib/vdso_kernel/datastore.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..c9cd269b1ed1b6cdd5fdf9fe929d0b778314b962
> --- /dev/null
> +++ b/lib/vdso_kernel/datastore.c
> @@ -0,0 +1,99 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/linkage.h>
> +#include <linux/mmap_lock.h>
> +#include <linux/mm.h>
> +#include <linux/time_namespace.h>
> +#include <linux/types.h>
> +#include <linux/vdso_datastore.h>
> +#include <vdso/datapage.h>
> +
> +/*
> + * The vDSO data page.
> + */
> +static union vdso_data_store vdso_time_data_store __page_aligned_data;
> +struct vdso_time_data *vdso_k_time_data = vdso_time_data_store.data;
> +static_assert(sizeof(vdso_time_data_store) == PAGE_SIZE);
> +
> +static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
> +			     struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> +	struct page *timens_page = find_timens_vvar_page(vma);
> +	unsigned long addr, pfn;
> +	vm_fault_t err;
> +
> +	switch (vmf->pgoff) {
> +	case VDSO_TIME_PAGE_OFFSET:
> +		pfn = __phys_to_pfn(__pa_symbol(vdso_k_time_data));
> +		if (timens_page) {
> +			/*
> +			 * Fault in VVAR page too, since it will be accessed
> +			 * to get clock data anyway.
> +			 */
> +			addr = vmf->address + VDSO_TIMENS_PAGE_OFFSET * PAGE_SIZE;
> +			err = vmf_insert_pfn(vma, addr, pfn);
> +			if (unlikely(err & VM_FAULT_ERROR))
> +				return err;
> +			pfn = page_to_pfn(timens_page);
> +		}
> +		break;
> +	case VDSO_TIMENS_PAGE_OFFSET:
> +		/*
> +		 * If a task belongs to a time namespace then a namespace
> +		 * specific VVAR is mapped with the VVAR_DATA_PAGE_OFFSET and
> +		 * the real VVAR page is mapped with the VVAR_TIMENS_PAGE_OFFSET
> +		 * offset.
> +		 * See also the comment near timens_setup_vdso_data().
> +		 */
> +		if (!IS_ENABLED(CONFIG_TIME_NS) || !timens_page)
> +			return VM_FAULT_SIGBUS;
> +		pfn = __phys_to_pfn(__pa_symbol(vdso_k_time_data));
> +		break;
> +	default:
> +		return VM_FAULT_SIGBUS;
> +	}
> +
> +	return vmf_insert_pfn(vma, vmf->address, pfn);
> +}
> +
> +const struct vm_special_mapping vdso_vvar_mapping = {
> +	.name	= "[vvar]",
> +	.fault	= vvar_fault,
> +};
> +
> +struct vm_area_struct *vdso_install_vvar_mapping(struct mm_struct *mm, unsigned long addr)
> +{
> +	return _install_special_mapping(mm, addr, VDSO_NR_PAGES * PAGE_SIZE,
> +					VM_READ | VM_MAYREAD | VM_IO | VM_DONTDUMP | VM_PFNMAP,
> +					&vdso_vvar_mapping);
> +}
> +
> +#ifdef CONFIG_TIME_NS
> +/*
> + * The vvar page layout depends on whether a task belongs to the root or
> + * non-root time namespace. Whenever a task changes its namespace, the VVAR
> + * page tables are cleared and then they will be re-faulted with a
> + * corresponding layout.
> + * See also the comment near timens_setup_vdso_data() for details.
> + */
> +int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
> +{
> +	struct mm_struct *mm = task->mm;
> +	struct vm_area_struct *vma;
> +	VMA_ITERATOR(vmi, mm, 0);
> +
> +	mmap_read_lock(mm);
> +	for_each_vma(vmi, vma) {
> +		if (vma_is_special_mapping(vma, &vdso_vvar_mapping))
> +			zap_vma_pages(vma);
> +	}
> +	mmap_read_unlock(mm);
> +
> +	return 0;
> +}
> +#endif
> +
> +struct vdso_time_data *arch_get_vdso_data(void *vvar_page)
> +{
> +	return (struct vdso_time_data *)vvar_page;
> +}
>