vdso: Define standardized vdso_datapage

Define a common formet for the vdso datapage as a preparation for sharing
the VDSO implementation as a generic library.

The datastructures are based on the current x86 layout.

[ tglx: Massaged changelog ]

Signed-off-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Shijith Thotton <[email protected]>
Tested-by: Andre Przywara <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Russell King <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Paul Burton <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: Mark Salyzyn <[email protected]>
Cc: Peter Collingbourne <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Huw Davies <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

include/vdso/datapage.h

@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_DATAPAGE_H
+#define __VDSO_DATAPAGE_H
+
+#ifdef __KERNEL__
+
+#ifndef __ASSEMBLY__
+
+#include <linux/bits.h>
+#include <linux/time.h>
+#include <linux/types.h>
+
+#define VDSO_BASES	(CLOCK_TAI + 1)
+#define VDSO_HRES	(BIT(CLOCK_REALTIME)		| \
+			 BIT(CLOCK_MONOTONIC)		| \
+			 BIT(CLOCK_BOOTTIME)		| \
+			 BIT(CLOCK_TAI))
+#define VDSO_COARSE	(BIT(CLOCK_REALTIME_COARSE)	| \
+			 BIT(CLOCK_MONOTONIC_COARSE))
+#define VDSO_RAW	(BIT(CLOCK_MONOTONIC_RAW))
+
+#define CS_HRES_COARSE	0
+#define CS_RAW		1
+#define CS_BASES	(CS_RAW + 1)
+
+/**
+ * struct vdso_timestamp - basetime per clock_id
+ * @sec:	seconds
+ * @nsec:	nanoseconds
+ *
+ * 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
+ * the actual time.
+ *
+ * To be noticed that for highres clocks nsec is left-shifted by
+ * vdso_data.cs[x].shift.
+ */
+struct vdso_timestamp {
+	u64	sec;
+	u64	nsec;
+};
+
+/**
+ * struct vdso_data - vdso datapage representation
+ * @seq:		timebase sequence counter
+ * @clock_mode:		clock mode
+ * @cycle_last:		timebase at clocksource init
+ * @mask:		clocksource mask
+ * @mult:		clocksource multiplier
+ * @shift:		clocksource shift
+ * @basetime[clock_id]:	basetime per clock_id
+ * @tz_minuteswest:	minutes west of Greenwich
+ * @tz_dsttime:		type of DST correction
+ * @hrtimer_res:	hrtimer resolution
+ * @__unused:		unused
+ *
+ * vdso_data will be accessed by 64 bit and compat code at the same time
+ * so we should be careful before modifying this structure.
+ */
+struct vdso_data {
+	u32			seq;
+
+	s32			clock_mode;
+	u64			cycle_last;
+	u64			mask;
+	u32			mult;
+	u32			shift;
+
+	struct vdso_timestamp	basetime[VDSO_BASES];
+
+	s32			tz_minuteswest;
+	s32			tz_dsttime;
+	u32			hrtimer_res;
+	u32			__unused;
+};
+
+/*
+ * We use the hidden visibility to prevent the compiler from generating a GOT
+ * relocation. Not only is going through a GOT useless (the entry couldn't and
+ * must not be overridden by another library), it does not even work: the linker
+ * cannot generate an absolute address to the data page.
+ *
+ * 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")));
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __KERNEL__ */
+
+#endif /* __VDSO_DATAPAGE_H */