vdso: Add generic time data storage

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250204-vdso-store-rng-v3-5-13a4669dfc8c@linutronix.de

1 files changed, 33 insertions, 8 deletions

diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index d967baa0cd0c..b3d8087488ff 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 +138,34 @@ 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 struct vdso_time_data vdso_u_time_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
+};
+
+#endif /* CONFIG_GENERIC_VDSO_DATA_STORE */
+
 /*
  * The generic vDSO implementation requires that gettimeofday.h
  * provides:
@@ -164,6 +182,13 @@ union vdso_data_store {
 #include <asm/vdso/gettimeofday.h>
 #endif /* ENABLE_COMPAT_VDSO */
 
+#else /* !__ASSEMBLY__ */
+
+#define VDSO_VVAR_SYMS						\
+	PROVIDE(vdso_u_data = . - __VDSO_PAGES * PAGE_SIZE);	\
+	PROVIDE(vdso_u_time_data = vdso_u_data);		\
+
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __VDSO_DATAPAGE_H */