diff mbox series

[3/6] arm64/vdso: Add time napespace page

Message ID 20200416052618.804515-4-avagin@gmail.com (mailing list archive)
State New, archived
Headers show
Series arm64: add the time namespace support | expand

Commit Message

Andrei Vagin April 16, 2020, 5:26 a.m. UTC 
Allocate the time namespace page among VVAR pages.  Provide
__arch_get_timens_vdso_data() helper for VDSO code to get the
code-relative position of VVARs on that special page.

If a task belongs to a time namespace then the VVAR page which contains
the system wide VDSO data is replaced with a namespace specific page
which has the same layout as the VVAR page. That page has vdso_data->seq
set to 1 to enforce the slow path and vdso_data->clock_mode set to
VCLOCK_TIMENS to enforce the time namespace handling path.

The extra check in the case that vdso_data->seq is odd, e.g. a concurrent
update of the VDSO data is in progress, is not really affecting regular
tasks which are not part of a time namespace as the task is spin waiting
for the update to finish and vdso_data->seq to become even again.

If a time namespace task hits that code path, it invokes the corresponding
time getter function which retrieves the real VVAR page, reads host time
and then adds the offset for the requested clock which is stored in the
special VVAR page.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
---
 arch/arm64/include/asm/vdso.h                 |  6 ++++++
 .../include/asm/vdso/compat_gettimeofday.h    | 14 +++++++++++++
 arch/arm64/include/asm/vdso/gettimeofday.h    |  8 ++++++++
 arch/arm64/kernel/vdso.c                      | 20 ++++++++++++++++---
 arch/arm64/kernel/vdso/vdso.lds.S             |  5 ++++-
 arch/arm64/kernel/vdso32/vdso.lds.S           |  5 ++++-
 include/vdso/datapage.h                       |  1 +
 7 files changed, 54 insertions(+), 5 deletions(-)

Comments

Mark Rutland April 16, 2020, 10:45 a.m. UTC | #1 
Hi Andrei,

On Wed, Apr 15, 2020 at 10:26:15PM -0700, Andrei Vagin wrote:
> diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
> index 07468428fd29..351c145d3808 100644
> --- a/arch/arm64/include/asm/vdso.h
> +++ b/arch/arm64/include/asm/vdso.h
> @@ -12,6 +12,12 @@
>   */
>  #define VDSO_LBASE	0x0
>  
> +#ifdef CONFIG_TIME_NS
> +#define __VVAR_PAGES    2
> +#else
> +#define __VVAR_PAGES    1
> +#endif
> +
>  #ifndef __ASSEMBLY__
  
> +#ifdef CONFIG_TIME_NS
> +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void)
> +{
> +	const struct vdso_data *ret;
> +
> +	ret = _timens_data;
> +	OPTIMIZER_HIDE_VAR(ret);
> +
> +	return ret;
> +}
> +#endif

Sorry for the confusion here, but please either:

* Add a preparatory patch making __arch_get_vdso_data() use
  OPTIMIZER_HIDE_VAR(), and use OPTIMIZER_HIDE_VAR() here.

* Use the same assembly as __arch_get_vdso_data() currently does.

... and either way add a comment here:

	/* See __arch_get_vdso_data() */

... so taht the rationale is obvious.

[...]

> +enum vvar_pages {
> +	VVAR_DATA_PAGE_OFFSET = 0,
> +#ifdef CONFIG_TIME_NS
> +	VVAR_TIMENS_PAGE_OFFSET = 1,
> +#endif /* CONFIG_TIME_NS */
> +	VVAR_NR_PAGES = __VVAR_PAGES,
> +};

Pet peeve, but we don't need the initializers here, as enums start from
zero. The last element shouldn't have a trailing comma as we don't
expect to add elements after it in future.

Rather than assigning to VVAR_NR_PAGES, it'd be better to use a
BUILD_BUG_ON() to verify that it is the number we expect:

enum vvar_pages {
	VVAR_DATA_PAGE,
#ifdef CONFIG_TIME_NS
	VVAR_TIMENS_PAGE,
#endif
	VVAR_NR_PAGES
};

BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);

Thanks,
Mark.
Andrei Vagin April 23, 2020, 5:23 a.m. UTC | #2 
On Thu, Apr 16, 2020 at 11:45:27AM +0100, Mark Rutland wrote:
> Hi Andrei,
> 
> On Wed, Apr 15, 2020 at 10:26:15PM -0700, Andrei Vagin wrote:
> > diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
> > index 07468428fd29..351c145d3808 100644
> > --- a/arch/arm64/include/asm/vdso.h
> > +++ b/arch/arm64/include/asm/vdso.h
...
> > +#ifdef CONFIG_TIME_NS
> > +static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void)
> > +{
> > +	const struct vdso_data *ret;
> > +
> > +	ret = _timens_data;
> > +	OPTIMIZER_HIDE_VAR(ret);
> > +
> > +	return ret;
> > +}
> > +#endif
> 
> Sorry for the confusion here, but please either:
> 
> * Add a preparatory patch making __arch_get_vdso_data() use
>   OPTIMIZER_HIDE_VAR(), and use OPTIMIZER_HIDE_VAR() here.
> 
> * Use the same assembly as __arch_get_vdso_data() currently does.
> 
> ... and either way add a comment here:
> 
> 	/* See __arch_get_vdso_data() */
> 
> ... so taht the rationale is obvious.
> 
> [...]
> 
> > +enum vvar_pages {
> > +	VVAR_DATA_PAGE_OFFSET = 0,
> > +#ifdef CONFIG_TIME_NS
> > +	VVAR_TIMENS_PAGE_OFFSET = 1,
> > +#endif /* CONFIG_TIME_NS */
> > +	VVAR_NR_PAGES = __VVAR_PAGES,
> > +};
> 
> Pet peeve, but we don't need the initializers here, as enums start from
> zero. The last element shouldn't have a trailing comma as we don't
> expect to add elements after it in future.
> 
> Rather than assigning to VVAR_NR_PAGES, it'd be better to use a
> BUILD_BUG_ON() to verify that it is the number we expect:
> 
> enum vvar_pages {
> 	VVAR_DATA_PAGE,
> #ifdef CONFIG_TIME_NS
> 	VVAR_TIMENS_PAGE,
> #endif
> 	VVAR_NR_PAGES
> };
> 
> BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);

Hi Mark,

Thank you for the review. I have sent a fixed version of this patch in
replay to the origin patch.

Thanks,
Andrei
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/vdso.h b/arch/arm64/include/asm/vdso.h
index 07468428fd29..351c145d3808 100644
--- a/arch/arm64/include/asm/vdso.h
+++ b/arch/arm64/include/asm/vdso.h
@@ -12,6 +12,12 @@ 
  */
 #define VDSO_LBASE	0x0
 
+#ifdef CONFIG_TIME_NS
+#define __VVAR_PAGES    2
+#else
+#define __VVAR_PAGES    1
+#endif
+
 #ifndef __ASSEMBLY__
 
 #include <generated/vdso-offsets.h>
diff --git a/arch/arm64/include/asm/vdso/compat_gettimeofday.h b/arch/arm64/include/asm/vdso/compat_gettimeofday.h
index b6907ae78e53..6ce9cdf5e08b 100644
--- a/arch/arm64/include/asm/vdso/compat_gettimeofday.h
+++ b/arch/arm64/include/asm/vdso/compat_gettimeofday.h
@@ -7,6 +7,8 @@ 
 
 #ifndef __ASSEMBLY__
 
+#include <linux/compiler.h>
+
 #include <asm/unistd.h>
 #include <asm/errno.h>
 
@@ -152,6 +154,18 @@  static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
 	return ret;
 }
 
+#ifdef CONFIG_TIME_NS
+static __always_inline const struct vdso_data *__arch_get_timens_vdso_data(void)
+{
+	const struct vdso_data *ret;
+
+	ret = _timens_data;
+	OPTIMIZER_HIDE_VAR(ret);
+
+	return ret;
+}
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_VDSO_GETTIMEOFDAY_H */
diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h
index afba6ba332f8..cf39eae5eaaf 100644
--- a/arch/arm64/include/asm/vdso/gettimeofday.h
+++ b/arch/arm64/include/asm/vdso/gettimeofday.h
@@ -96,6 +96,14 @@  const struct vdso_data *__arch_get_vdso_data(void)
 	return _vdso_data;
 }
 
+#ifdef CONFIG_TIME_NS
+static __always_inline
+const struct vdso_data *__arch_get_timens_vdso_data(void)
+{
+	return _timens_data;
+}
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_VDSO_GETTIMEOFDAY_H */
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 6ac9cdeac5be..b3e7ce24e59b 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -46,6 +46,14 @@  enum arch_vdso_type {
 #define VDSO_TYPES		(ARM64_VDSO + 1)
 #endif /* CONFIG_COMPAT_VDSO */
 
+enum vvar_pages {
+	VVAR_DATA_PAGE_OFFSET = 0,
+#ifdef CONFIG_TIME_NS
+	VVAR_TIMENS_PAGE_OFFSET = 1,
+#endif /* CONFIG_TIME_NS */
+	VVAR_NR_PAGES = __VVAR_PAGES,
+};
+
 struct __vdso_abi {
 	const char *name;
 	const char *vdso_code_start;
@@ -81,6 +89,12 @@  static union {
 } vdso_data_store __page_aligned_data;
 struct vdso_data *vdso_data = vdso_data_store.data;
 
+
+struct vdso_data *arch_get_vdso_data(void *vvar_page)
+{
+	return (struct vdso_data *)(vvar_page);
+}
+
 static int __vdso_remap(enum arch_vdso_type arch_index,
 			const struct vm_special_mapping *sm,
 			struct vm_area_struct *new_vma)
@@ -182,7 +196,7 @@  static int __setup_additional_pages(enum arch_vdso_type arch_index,
 
 	vdso_text_len = vdso_lookup[arch_index].vdso_pages << PAGE_SHIFT;
 	/* Be sure to map the data page */
-	vdso_mapping_len = vdso_text_len + PAGE_SIZE;
+	vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE;
 
 	vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
 	if (IS_ERR_VALUE(vdso_base)) {
@@ -190,13 +204,13 @@  static int __setup_additional_pages(enum arch_vdso_type arch_index,
 		goto up_fail;
 	}
 
-	ret = _install_special_mapping(mm, vdso_base, PAGE_SIZE,
+	ret = _install_special_mapping(mm, vdso_base, VVAR_NR_PAGES * PAGE_SIZE,
 				       VM_READ|VM_MAYREAD|VM_PFNMAP,
 				       vdso_lookup[arch_index].dm);
 	if (IS_ERR(ret))
 		goto up_fail;
 
-	vdso_base += PAGE_SIZE;
+	vdso_base += VVAR_NR_PAGES * PAGE_SIZE;
 	mm->context.vdso = (void *)vdso_base;
 	ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
 				       VM_READ|VM_EXEC|
diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
index 7ad2d3a0cd48..d808ad31e01f 100644
--- a/arch/arm64/kernel/vdso/vdso.lds.S
+++ b/arch/arm64/kernel/vdso/vdso.lds.S
@@ -17,7 +17,10 @@  OUTPUT_ARCH(aarch64)
 
 SECTIONS
 {
-	PROVIDE(_vdso_data = . - PAGE_SIZE);
+	PROVIDE(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE);
+#ifdef CONFIG_TIME_NS
+	PROVIDE(_timens_data = _vdso_data + PAGE_SIZE);
+#endif
 	. = VDSO_LBASE + SIZEOF_HEADERS;
 
 	.hash		: { *(.hash) }			:text
diff --git a/arch/arm64/kernel/vdso32/vdso.lds.S b/arch/arm64/kernel/vdso32/vdso.lds.S
index a3944927eaeb..06cc60a9630f 100644
--- a/arch/arm64/kernel/vdso32/vdso.lds.S
+++ b/arch/arm64/kernel/vdso32/vdso.lds.S
@@ -17,7 +17,10 @@  OUTPUT_ARCH(arm)
 
 SECTIONS
 {
-	PROVIDE_HIDDEN(_vdso_data = . - PAGE_SIZE);
+	PROVIDE_HIDDEN(_vdso_data = . - __VVAR_PAGES * PAGE_SIZE);
+#ifdef CONFIG_TIME_NS
+	PROVIDE_HIDDEN(_timens_data = _vdso_data + PAGE_SIZE);
+#endif
 	. = VDSO_LBASE + SIZEOF_HEADERS;
 
 	.hash		: { *(.hash) }			:text
diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index 5cbc9fcbfd45..2022e8c653c1 100644
--- a/include/vdso/datapage.h
+++ b/include/vdso/datapage.h
@@ -109,6 +109,7 @@  struct vdso_data {
  * 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")));
 
 /*
  * The generic vDSO implementation requires that gettimeofday.h