ARM: 8930/1: Add support for generic vDSO

The arm vDSO library requires some adaptations to take advantage of
the newly introduced generic vDSO library.

Introduce the following changes:
- Modification vdso.c to be compliant with the common vdso datapage
- Use of lib/vdso for gettimeofday
- Implementation of elf note

Signed-off-by: Vincenzo Frascino <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/vdso/gettimeofday.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2018 ARM Limited
+ */
+#ifndef __ASM_VDSO_GETTIMEOFDAY_H
+#define __ASM_VDSO_GETTIMEOFDAY_H
+
+#ifndef __ASSEMBLY__
+
+#include <asm/barrier.h>
+#include <asm/cp15.h>
+#include <asm/unistd.h>
+#include <uapi/linux/time.h>
+
+extern struct vdso_data *__get_datapage(void);
+
+static __always_inline int gettimeofday_fallback(
+				struct __kernel_old_timeval *_tv,
+				struct timezone *_tz)
+{
+	register struct timezone *tz asm("r1") = _tz;
+	register struct __kernel_old_timeval *tv asm("r0") = _tv;
+	register long ret asm ("r0");
+	register long nr asm("r7") = __NR_gettimeofday;
+
+	asm volatile(
+	"	swi #0\n"
+	: "=r" (ret)
+	: "r" (tv), "r" (tz), "r" (nr)
+	: "memory");
+
+	return ret;
+}
+
+static __always_inline long clock_gettime_fallback(
+					clockid_t _clkid,
+					struct __kernel_timespec *_ts)
+{
+	register struct __kernel_timespec *ts asm("r1") = _ts;
+	register clockid_t clkid asm("r0") = _clkid;
+	register long ret asm ("r0");
+	register long nr asm("r7") = __NR_clock_gettime64;
+
+	asm volatile(
+	"	swi #0\n"
+	: "=r" (ret)
+	: "r" (clkid), "r" (ts), "r" (nr)
+	: "memory");
+
+	return ret;
+}
+
+static __always_inline u64 __arch_get_hw_counter(int clock_mode)
+{
+#ifdef CONFIG_ARM_ARCH_TIMER
+	u64 cycle_now;
+
+	isb();
+	cycle_now = read_sysreg(CNTVCT);
+
+	return cycle_now;
+#else
+	return -EINVAL; /* use fallback */
+#endif
+}
+
+static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
+{
+	return __get_datapage();
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_GETTIMEOFDAY_H */

arch/arm/include/asm/vdso/vsyscall.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_VDSO_VSYSCALL_H
+#define __ASM_VDSO_VSYSCALL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/timekeeper_internal.h>
+#include <vdso/datapage.h>
+#include <asm/cacheflush.h>
+
+extern struct vdso_data *vdso_data;
+extern bool cntvct_ok;
+
+static __always_inline
+bool tk_is_cntvct(const struct timekeeper *tk)
+{
+	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
+		return false;
+
+	if (!tk->tkr_mono.clock->archdata.vdso_direct)
+		return false;
+
+	return true;
+}
+
+/*
+ * Update the vDSO data page to keep in sync with kernel timekeeping.
+ */
+static __always_inline
+struct vdso_data *__arm_get_k_vdso_data(void)
+{
+	return vdso_data;
+}
+#define __arch_get_k_vdso_data __arm_get_k_vdso_data
+
+static __always_inline
+int __arm_update_vdso_data(void)
+{
+	return !cntvct_ok;
+}
+#define __arch_update_vdso_data __arm_update_vdso_data
+
+static __always_inline
+int __arm_get_clock_mode(struct timekeeper *tk)
+{
+	u32 __tk_is_cntvct = tk_is_cntvct(tk);
+
+	return __tk_is_cntvct;
+}
+#define __arch_get_clock_mode __arm_get_clock_mode
+
+static __always_inline
+int __arm_use_vsyscall(struct vdso_data *vdata)
+{
+	return vdata[CS_HRES_COARSE].clock_mode;
+}
+#define __arch_use_vsyscall __arm_use_vsyscall
+
+static __always_inline
+void __arm_sync_vdso_data(struct vdso_data *vdata)
+{
+	flush_dcache_page(virt_to_page(vdata));
+}
+#define __arch_sync_vdso_data __arm_sync_vdso_data
+
+/* The asm-generic header needs to be included after the definitions above */
+#include <asm-generic/vdso/vsyscall.h>
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_VSYSCALL_H */

arch/arm/include/asm/vdso_datapage.h

···
 
 #ifndef __ASSEMBLY__
 
+#include <vdso/datapage.h>
 #include <asm/page.h>
 
-/* Try to be cache-friendly on systems that don't implement the
- * generic timer: fit the unconditionally updated fields in the first
- * 32 bytes.
- */
-struct vdso_data {
-	u32 seq_count;		/* sequence count - odd during updates */
-	u16 tk_is_cntvct;	/* fall back to syscall if false */
-	u16 cs_shift;		/* clocksource shift */
-	u32 xtime_coarse_sec;	/* coarse time */
-	u32 xtime_coarse_nsec;
-
-	u32 wtm_clock_sec;	/* wall to monotonic offset */
-	u32 wtm_clock_nsec;
-	u32 xtime_clock_sec;	/* CLOCK_REALTIME - seconds */
-	u32 cs_mult;		/* clocksource multiplier */
-
-	u64 cs_cycle_last;	/* last cycle value */
-	u64 cs_mask;		/* clocksource mask */
-
-	u64 xtime_clock_snsec;	/* CLOCK_REALTIME sub-ns base */
-	u32 tz_minuteswest;	/* timezone info for gettimeofday(2) */
-	u32 tz_dsttime;
-};
-
 union vdso_data_store {
-	struct vdso_data data;
-	u8 page[PAGE_SIZE];
+	struct vdso_data	data[CS_BASES];
+	u8			page[PAGE_SIZE];
 };
 
 #endif /* !__ASSEMBLY__ */

arch/arm/kernel/vdso.c

···
 #include <asm/vdso.h>
 #include <asm/vdso_datapage.h>
 #include <clocksource/arm_arch_timer.h>
+#include <vdso/helpers.h>
+#include <vdso/vsyscall.h>
 
 #define MAX_SYMNAME	64
 
···
  * The VDSO data page.
  */
 static union vdso_data_store vdso_data_store __page_aligned_data;
-static struct vdso_data *vdso_data = &vdso_data_store.data;
+struct vdso_data *vdso_data = vdso_data_store.data;
 
 static struct page *vdso_data_page __ro_after_init;
 static const struct vm_special_mapping vdso_data_mapping = {
···
 /* Cached result of boot-time check for whether the arch timer exists,
  * and if so, whether the virtual counter is useable.
  */
-static bool cntvct_ok __ro_after_init;
+bool cntvct_ok __ro_after_init;
 
 static bool __init cntvct_functional(void)
 {
···
 		mm->context.vdso = addr;
 }
 
-static void vdso_write_begin(struct vdso_data *vdata)
-{
-	++vdso_data->seq_count;
-	smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
-}
-
-static void vdso_write_end(struct vdso_data *vdata)
-{
-	smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
-	++vdso_data->seq_count;
-}
-
-static bool tk_is_cntvct(const struct timekeeper *tk)
-{
-	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
-		return false;
-
-	if (!tk->tkr_mono.clock->archdata.vdso_direct)
-		return false;
-
-	return true;
-}
-
-/**
- * update_vsyscall - update the vdso data page
- *
- * Increment the sequence counter, making it odd, indicating to
- * userspace that an update is in progress.  Update the fields used
- * for coarse clocks and, if the architected system timer is in use,
- * the fields used for high precision clocks.  Increment the sequence
- * counter again, making it even, indicating to userspace that the
- * update is finished.
- *
- * Userspace is expected to sample seq_count before reading any other
- * fields from the data page.  If seq_count is odd, userspace is
- * expected to wait until it becomes even.  After copying data from
- * the page, userspace must sample seq_count again; if it has changed
- * from its previous value, userspace must retry the whole sequence.
- *
- * Calls to update_vsyscall are serialized by the timekeeping core.
- */
-void update_vsyscall(struct timekeeper *tk)
-{
-	struct timespec64 *wtm = &tk->wall_to_monotonic;
-
-	if (!cntvct_ok) {
-		/* The entry points have been zeroed, so there is no
-		 * point in updating the data page.
-		 */
-		return;
-	}
-
-	vdso_write_begin(vdso_data);
-
-	vdso_data->tk_is_cntvct			= tk_is_cntvct(tk);
-	vdso_data->xtime_coarse_sec		= tk->xtime_sec;
-	vdso_data->xtime_coarse_nsec		= (u32)(tk->tkr_mono.xtime_nsec >>
-							tk->tkr_mono.shift);
-	vdso_data->wtm_clock_sec		= wtm->tv_sec;
-	vdso_data->wtm_clock_nsec		= wtm->tv_nsec;
-
-	if (vdso_data->tk_is_cntvct) {
-		vdso_data->cs_cycle_last	= tk->tkr_mono.cycle_last;
-		vdso_data->xtime_clock_sec	= tk->xtime_sec;
-		vdso_data->xtime_clock_snsec	= tk->tkr_mono.xtime_nsec;
-		vdso_data->cs_mult		= tk->tkr_mono.mult;
-		vdso_data->cs_shift		= tk->tkr_mono.shift;
-		vdso_data->cs_mask		= tk->tkr_mono.mask;
-	}
-
-	vdso_write_end(vdso_data);
-
-	flush_dcache_page(virt_to_page(vdso_data));
-}
-
-void update_vsyscall_tz(void)
-{
-	vdso_data->tz_minuteswest	= sys_tz.tz_minuteswest;
-	vdso_data->tz_dsttime		= sys_tz.tz_dsttime;
-	flush_dcache_page(virt_to_page(vdso_data));
-}

arch/arm/mm/Kconfig

···
 	bool "Enable VDSO for acceleration of some system calls"
 	depends on AEABI && MMU && CPU_V7
 	default y if ARM_ARCH_TIMER
+	select HAVE_GENERIC_VDSO
 	select GENERIC_TIME_VSYSCALL
+	select GENERIC_VDSO_32
+	select GENERIC_GETTIMEOFDAY
 	help
 	  Place in the process address space an ELF shared object
 	  providing fast implementations of gettimeofday and

arch/arm/vdso/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
+
+# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
+# the inclusion of generic Makefile.
+ARCH_REL_TYPE_ABS := R_ARM_JUMP_SLOT|R_ARM_GLOB_DAT|R_ARM_ABS32
+include $(srctree)/lib/vdso/Makefile
+
 hostprogs-y := vdsomunge
 
-obj-vdso := vgettimeofday.o datapage.o
+obj-vdso := vgettimeofday.o datapage.o note.o
 
 # Build rules
 targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.so.raw vdso.lds
···
 
 # Force -O2 to avoid libgcc dependencies
 CFLAGS_REMOVE_vgettimeofday.o = -pg -Os
+ifeq ($(c-gettimeofday-y),)
 CFLAGS_vgettimeofday.o = -O2
+else
+CFLAGS_vgettimeofday.o = -O2 -include $(c-gettimeofday-y)
+endif
 
 # Disable gcov profiling for VDSO code
 GCOV_PROFILE := n
···
 
 # Link rule for the .so file
 $(obj)/vdso.so.raw: $(obj)/vdso.lds $(obj-vdso) FORCE
-	$(call if_changed,ld)
+	$(call if_changed,vdsold_and_vdso_check)
 
 $(obj)/vdso.so.dbg: $(obj)/vdso.so.raw $(obj)/vdsomunge FORCE
 	$(call if_changed,vdsomunge)
···
 $(obj)/%.so: OBJCOPYFLAGS := -S
 $(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
+
+# Actual build commands
+quiet_cmd_vdsold_and_vdso_check = LD      $@
+      cmd_vdsold_and_vdso_check = $(cmd_ld); $(cmd_vdso_check)
 
 quiet_cmd_vdsomunge = MUNGE   $@
       cmd_vdsomunge = $(objtree)/$(obj)/vdsomunge $< $@

arch/arm/vdso/note.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2012-2018 ARM Limited
+ *
+ * This supplies .note.* sections to go into the PT_NOTE inside the vDSO text.
+ * Here we can supply some information useful to userland.
+ */
+
+#include <linux/uts.h>
+#include <linux/version.h>
+#include <linux/elfnote.h>
+#include <linux/build-salt.h>
+
+ELFNOTE32("Linux", 0, LINUX_VERSION_CODE);
+BUILD_SALT;

arch/arm/vdso/vgettimeofday.c

···
 // SPDX-License-Identifier: GPL-2.0-only
 /*
+ * ARM userspace implementations of gettimeofday() and similar.
+ *
  * Copyright 2015 Mentor Graphics Corporation.
  */
-
-#include <linux/compiler.h>
-#include <linux/hrtimer.h>
 #include <linux/time.h>
-#include <asm/barrier.h>
-#include <asm/bug.h>
-#include <asm/cp15.h>
-#include <asm/page.h>
-#include <asm/unistd.h>
-#include <asm/vdso_datapage.h>
+#include <linux/types.h>
 
-#ifndef CONFIG_AEABI
-#error This code depends on AEABI system call conventions
-#endif
-
-extern struct vdso_data *__get_datapage(void);
-
-static notrace u32 __vdso_read_begin(const struct vdso_data *vdata)
+int __vdso_clock_gettime(clockid_t clock,
+			 struct old_timespec32 *ts)
 {
-	u32 seq;
-repeat:
-	seq = READ_ONCE(vdata->seq_count);
-	if (seq & 1) {
-		cpu_relax();
-		goto repeat;
-	}
-	return seq;
+	return __cvdso_clock_gettime32(clock, ts);
 }
 
-static notrace u32 vdso_read_begin(const struct vdso_data *vdata)
+int __vdso_gettimeofday(struct __kernel_old_timeval *tv,
+			struct timezone *tz)
 {
-	u32 seq;
-
-	seq = __vdso_read_begin(vdata);
-
-	smp_rmb(); /* Pairs with smp_wmb in vdso_write_end */
-	return seq;
-}
-
-static notrace int vdso_read_retry(const struct vdso_data *vdata, u32 start)
-{
-	smp_rmb(); /* Pairs with smp_wmb in vdso_write_begin */
-	return vdata->seq_count != start;
-}
-
-static notrace long clock_gettime_fallback(clockid_t _clkid,
-					   struct timespec *_ts)
-{
-	register struct timespec *ts asm("r1") = _ts;
-	register clockid_t clkid asm("r0") = _clkid;
-	register long ret asm ("r0");
-	register long nr asm("r7") = __NR_clock_gettime;
-
-	asm volatile(
-	"	swi #0\n"
-	: "=r" (ret)
-	: "r" (clkid), "r" (ts), "r" (nr)
-	: "memory");
-
-	return ret;
-}
-
-static notrace int do_realtime_coarse(struct timespec *ts,
-				      struct vdso_data *vdata)
-{
-	u32 seq;
-
-	do {
-		seq = vdso_read_begin(vdata);
-
-		ts->tv_sec = vdata->xtime_coarse_sec;
-		ts->tv_nsec = vdata->xtime_coarse_nsec;
-
-	} while (vdso_read_retry(vdata, seq));
-
-	return 0;
-}
-
-static notrace int do_monotonic_coarse(struct timespec *ts,
-				       struct vdso_data *vdata)
-{
-	struct timespec tomono;
-	u32 seq;
-
-	do {
-		seq = vdso_read_begin(vdata);
-
-		ts->tv_sec = vdata->xtime_coarse_sec;
-		ts->tv_nsec = vdata->xtime_coarse_nsec;
-
-		tomono.tv_sec = vdata->wtm_clock_sec;
-		tomono.tv_nsec = vdata->wtm_clock_nsec;
-
-	} while (vdso_read_retry(vdata, seq));
-
-	ts->tv_sec += tomono.tv_sec;
-	timespec_add_ns(ts, tomono.tv_nsec);
-
-	return 0;
-}
-
-#ifdef CONFIG_ARM_ARCH_TIMER
-
-static notrace u64 get_ns(struct vdso_data *vdata)
-{
-	u64 cycle_delta;
-	u64 cycle_now;
-	u64 nsec;
-
-	isb();
-	cycle_now = read_sysreg(CNTVCT);
-
-	cycle_delta = (cycle_now - vdata->cs_cycle_last) & vdata->cs_mask;
-
-	nsec = (cycle_delta * vdata->cs_mult) + vdata->xtime_clock_snsec;
-	nsec >>= vdata->cs_shift;
-
-	return nsec;
-}
-
-static notrace int do_realtime(struct timespec *ts, struct vdso_data *vdata)
-{
-	u64 nsecs;
-	u32 seq;
-
-	do {
-		seq = vdso_read_begin(vdata);
-
-		if (!vdata->tk_is_cntvct)
-			return -1;
-
-		ts->tv_sec = vdata->xtime_clock_sec;
-		nsecs = get_ns(vdata);
-
-	} while (vdso_read_retry(vdata, seq));
-
-	ts->tv_nsec = 0;
-	timespec_add_ns(ts, nsecs);
-
-	return 0;
-}
-
-static notrace int do_monotonic(struct timespec *ts, struct vdso_data *vdata)
-{
-	struct timespec tomono;
-	u64 nsecs;
-	u32 seq;
-
-	do {
-		seq = vdso_read_begin(vdata);
-
-		if (!vdata->tk_is_cntvct)
-			return -1;
-
-		ts->tv_sec = vdata->xtime_clock_sec;
-		nsecs = get_ns(vdata);
-
-		tomono.tv_sec = vdata->wtm_clock_sec;
-		tomono.tv_nsec = vdata->wtm_clock_nsec;
-
-	} while (vdso_read_retry(vdata, seq));
-
-	ts->tv_sec += tomono.tv_sec;
-	ts->tv_nsec = 0;
-	timespec_add_ns(ts, nsecs + tomono.tv_nsec);
-
-	return 0;
-}
-
-#else /* CONFIG_ARM_ARCH_TIMER */
-
-static notrace int do_realtime(struct timespec *ts, struct vdso_data *vdata)
-{
-	return -1;
-}
-
-static notrace int do_monotonic(struct timespec *ts, struct vdso_data *vdata)
-{
-	return -1;
-}
-
-#endif /* CONFIG_ARM_ARCH_TIMER */
-
-notrace int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
-{
-	struct vdso_data *vdata;
-	int ret = -1;
-
-	vdata = __get_datapage();
-
-	switch (clkid) {
-	case CLOCK_REALTIME_COARSE:
-		ret = do_realtime_coarse(ts, vdata);
-		break;
-	case CLOCK_MONOTONIC_COARSE:
-		ret = do_monotonic_coarse(ts, vdata);
-		break;
-	case CLOCK_REALTIME:
-		ret = do_realtime(ts, vdata);
-		break;
-	case CLOCK_MONOTONIC:
-		ret = do_monotonic(ts, vdata);
-		break;
-	default:
-		break;
-	}
-
-	if (ret)
-		ret = clock_gettime_fallback(clkid, ts);
-
-	return ret;
-}
-
-static notrace long gettimeofday_fallback(struct timeval *_tv,
-					  struct timezone *_tz)
-{
-	register struct timezone *tz asm("r1") = _tz;
-	register struct timeval *tv asm("r0") = _tv;
-	register long ret asm ("r0");
-	register long nr asm("r7") = __NR_gettimeofday;
-
-	asm volatile(
-	"	swi #0\n"
-	: "=r" (ret)
-	: "r" (tv), "r" (tz), "r" (nr)
-	: "memory");
-
-	return ret;
-}
-
-notrace int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
-{
-	struct timespec ts;
-	struct vdso_data *vdata;
-	int ret;
-
-	vdata = __get_datapage();
-
-	ret = do_realtime(&ts, vdata);
-	if (ret)
-		return gettimeofday_fallback(tv, tz);
-
-	if (tv) {
-		tv->tv_sec = ts.tv_sec;
-		tv->tv_usec = ts.tv_nsec / 1000;
-	}
-	if (tz) {
-		tz->tz_minuteswest = vdata->tz_minuteswest;
-		tz->tz_dsttime = vdata->tz_dsttime;
-	}
-
-	return ret;
+	return __cvdso_gettimeofday(tv, tz);
 }
 
 /* Avoid unresolved references emitted by GCC */