[PATCH v5 01/12] arm: vdso: rename vdso_datapage variables

* [PATCH v5 01/12] arm: vdso: rename vdso_datapage variables
@ 2017-11-06 21:00 ` Mark Salyzyn
  0 siblings, 0 replies; 2+ messages in thread
From: Mark Salyzyn @ 2017-11-06 21:00 UTC (permalink / raw)
  To: linux-kernel
  Cc: Mark Salyzyn, James Morse, Russell King, Catalin Marinas,
	Will Deacon, Andy Lutomirski, Dmitry Safonov, John Stultz,
	Mark Rutland, Laura Abbott, Kees Cook, Ard Biesheuvel,
	Andy Gross, Kevin Brodsky, Andrew Pinski, Thomas Gleixner,
	linux-arm-kernel

Take an effort to recode the arm64 vdso code from assembler to C
previously submitted by Andrew Pinski <apinski@cavium.com>, rework
it for use in both arm and arm64, overlapping any optimizations
for each architecture. But instead of landing it in arm64, land the
result into lib/vdso and unify both implementations to simplify
future maintenance.

Rename seq_count to tb_seq_count. Rename tk_is_cntvct to use_syscall.
Rename cs_mult to cs_mono_mult. All to align with the variables in the
arm64 vdso datapage. Rework vdso_read_begin() and vdso_read_retry()
functions to reflect modern access patterns for tb_seq_count field.

Update copyright message to reflect the start of the contributions in
this series.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Andy Gross <andy.gross@linaro.org>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Andrew Pinski <apinski@cavium.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org

v2:
- split first CL into 1 of 7 pieces

v4:
- update commit message to reflect reasoning

v5:
- rebase

---
 arch/arm/include/asm/vdso_datapage.h |  6 ++--
 arch/arm/kernel/vdso.c               | 17 +++++-----
 arch/arm/vdso/vgettimeofday.c        | 61 +++++++++++++++++++-----------------
 3 files changed, 45 insertions(+), 39 deletions(-)

diff --git a/arch/arm/include/asm/vdso_datapage.h b/arch/arm/include/asm/vdso_datapage.h
index 9be259442fca..fa3e1856244d 100644
--- a/arch/arm/include/asm/vdso_datapage.h
+++ b/arch/arm/include/asm/vdso_datapage.h
@@ -29,8 +29,8 @@
  * 32 bytes.
  */
 struct vdso_data {
-	u32 seq_count;		/* sequence count - odd during updates */
-	u16 tk_is_cntvct;	/* fall back to syscall if false */
+	u32 tb_seq_count;	/* sequence count - odd during updates */
+	u16 use_syscall;	/* fall back to syscall if true */
 	u16 cs_shift;		/* clocksource shift */
 	u32 xtime_coarse_sec;	/* coarse time */
 	u32 xtime_coarse_nsec;
@@ -38,7 +38,7 @@ struct vdso_data {
 	u32 wtm_clock_sec;	/* wall to monotonic offset */
 	u32 wtm_clock_nsec;
 	u32 xtime_clock_sec;	/* CLOCK_REALTIME - seconds */
-	u32 cs_mult;		/* clocksource multiplier */
+	u32 cs_mono_mult;	/* clocksource multiplier */
 
 	u64 cs_cycle_last;	/* last cycle value */
 	u64 cs_mask;		/* clocksource mask */
diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c
index a4d6dc0f2427..aed84b659cc5 100644
--- a/arch/arm/kernel/vdso.c
+++ b/arch/arm/kernel/vdso.c
@@ -274,14 +274,14 @@ void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 
 static void vdso_write_begin(struct vdso_data *vdata)
 {
-	++vdso_data->seq_count;
+	++vdso_data->tb_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;
+	++vdso_data->tb_seq_count;
 }
 
 static bool tk_is_cntvct(const struct timekeeper *tk)
@@ -305,10 +305,10 @@ static bool tk_is_cntvct(const struct timekeeper *tk)
  * 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
+ * Userspace is expected to sample tb_seq_count before reading any other
+ * fields from the data page.  If tb_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
+ * the page, userspace must sample tb_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.
@@ -326,18 +326,19 @@ void update_vsyscall(struct timekeeper *tk)
 
 	vdso_write_begin(vdso_data);
 
-	vdso_data->tk_is_cntvct			= tk_is_cntvct(tk);
+	vdso_data->use_syscall			= !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) {
+	if (!vdso_data->use_syscall) {
 		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_mono_mult		= tk->tkr_mono.mult;
+		/* tkr_mono.shift == tkr_raw.shift */
 		vdso_data->cs_shift		= tk->tkr_mono.shift;
 		vdso_data->cs_mask		= tk->tkr_mono.mask;
 	}
diff --git a/arch/arm/vdso/vgettimeofday.c b/arch/arm/vdso/vgettimeofday.c
index 79214d5ff097..8cf13af1323c 100644
--- a/arch/arm/vdso/vgettimeofday.c
+++ b/arch/arm/vdso/vgettimeofday.c
@@ -1,18 +1,25 @@
 /*
- * Copyright 2015 Mentor Graphics Corporation.
+ * Userspace implementations of gettimeofday() and friends.
  *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; version 2 of the
- * License.
+ * Copyright (C) 2017 Cavium, Inc.
+ * Copyright (C) 2015 Mentor Graphics Corporation
+ * Copyright (C) 2012 ARM Limited
  *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Will Deacon <will.deacon@arm.com>
+ * Rewriten from arch64 version into C by: Andrew Pinski <apinski@cavium.com>
+ * Reworked and rebased over arm version by: Mark Salyzyn <salyzyn@android.com>
  */
 
 #include <linux/compiler.h>
@@ -31,32 +38,30 @@
 
 extern struct vdso_data *__get_datapage(void);
 
-static notrace u32 __vdso_read_begin(const struct vdso_data *vdata)
-{
-	u32 seq;
-repeat:
-	seq = ACCESS_ONCE(vdata->seq_count);
-	if (seq & 1) {
-		cpu_relax();
-		goto repeat;
-	}
-	return seq;
-}
-
 static notrace u32 vdso_read_begin(const struct vdso_data *vdata)
 {
 	u32 seq;
 
-	seq = __vdso_read_begin(vdata);
+	do {
+		seq = READ_ONCE(vdata->tb_seq_count);
+
+		if ((seq & 1) == 0)
+			break;
 
-	smp_rmb(); /* Pairs with smp_wmb in vdso_write_end */
+		cpu_relax();
+	} while (true);
+
+	smp_rmb(); /* Pairs with second smp_wmb in update_vsyscall */
 	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;
+	u32 seq;
+
+	smp_rmb(); /* Pairs with first smp_wmb in update_vsyscall */
+	seq = READ_ONCE(vdata->tb_seq_count);
+	return seq != start;
 }
 
 static notrace long clock_gettime_fallback(clockid_t _clkid,
@@ -127,7 +132,7 @@ static notrace u64 get_ns(struct vdso_data *vdata)
 
 	cycle_delta = (cycle_now - vdata->cs_cycle_last) & vdata->cs_mask;
 
-	nsec = (cycle_delta * vdata->cs_mult) + vdata->xtime_clock_snsec;
+	nsec = (cycle_delta * vdata->cs_mono_mult) + vdata->xtime_clock_snsec;
 	nsec >>= vdata->cs_shift;
 
 	return nsec;
@@ -141,7 +146,7 @@ static notrace int do_realtime(struct timespec *ts, struct vdso_data *vdata)
 	do {
 		seq = vdso_read_begin(vdata);
 
-		if (!vdata->tk_is_cntvct)
+		if (vdata->use_syscall)
 			return -1;
 
 		ts->tv_sec = vdata->xtime_clock_sec;
@@ -164,7 +169,7 @@ static notrace int do_monotonic(struct timespec *ts, struct vdso_data *vdata)
 	do {
 		seq = vdso_read_begin(vdata);
 
-		if (!vdata->tk_is_cntvct)
+		if (vdata->use_syscall)
 			return -1;
 
 		ts->tv_sec = vdata->xtime_clock_sec;
-- 
2.15.0.403.gc27cc4dac6-goog

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