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authorVincenzo Frascino <vincenzo.frascino@arm.com>2019-06-21 10:52:29 +0100
committerThomas Gleixner <tglx@linutronix.de>2019-06-22 21:21:05 +0200
commit00b26474c2f1613d7ab894c525f775c67c8a9e8f (patch)
treeec821728fc16277806e520618650cbbdb5159575 /include/vdso
parent361f8aee9b093526297d567a9dc2f6cbf746e5f9 (diff)
lib/vdso: Provide generic VDSO implementation
In the last few years the kernel gained quite some architecture specific vdso implementations which contain very similar code. Introduce a generic VDSO implementation of gettimeofday() which will be shareable between architectures once they are converted over. The implementation is based on the current x86 VDSO code. [ tglx: Massaged changelog and made the kernel doc tabular ] Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Shijith Thotton <sthotton@marvell.com> Tested-by: Andre Przywara <andre.przywara@arm.com> Cc: linux-arch@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-mips@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Russell King <linux@armlinux.org.uk> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: Paul Burton <paul.burton@mips.com> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Mark Salyzyn <salyzyn@android.com> Cc: Peter Collingbourne <pcc@google.com> Cc: Shuah Khan <shuah@kernel.org> Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Huw Davies <huw@codeweavers.com> Link: https://lkml.kernel.org/r/20190621095252.32307-3-vincenzo.frascino@arm.com
Diffstat (limited to 'include/vdso')
-rw-r--r--include/vdso/helpers.h56
1 files changed, 56 insertions, 0 deletions
diff --git a/include/vdso/helpers.h b/include/vdso/helpers.h
new file mode 100644
index 000000000000..01641dbb68ef
--- /dev/null
+++ b/include/vdso/helpers.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_HELPERS_H
+#define __VDSO_HELPERS_H
+
+#ifndef __ASSEMBLY__
+
+#include <vdso/datapage.h>
+
+static __always_inline u32 vdso_read_begin(const struct vdso_data *vd)
+{
+ u32 seq;
+
+ while ((seq = READ_ONCE(vd->seq)) & 1)
+ cpu_relax();
+
+ smp_rmb();
+ return seq;
+}
+
+static __always_inline u32 vdso_read_retry(const struct vdso_data *vd,
+ u32 start)
+{
+ u32 seq;
+
+ smp_rmb();
+ seq = READ_ONCE(vd->seq);
+ return seq != start;
+}
+
+static __always_inline void vdso_write_begin(struct vdso_data *vd)
+{
+ /*
+ * WRITE_ONCE it is required otherwise the compiler can validly tear
+ * updates to vd[x].seq and it is possible that the value seen by the
+ * reader it is inconsistent.
+ */
+ WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
+ WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
+ smp_wmb();
+}
+
+static __always_inline void vdso_write_end(struct vdso_data *vd)
+{
+ smp_wmb();
+ /*
+ * WRITE_ONCE it is required otherwise the compiler can validly tear
+ * updates to vd[x].seq and it is possible that the value seen by the
+ * reader it is inconsistent.
+ */
+ WRITE_ONCE(vd[CS_HRES_COARSE].seq, vd[CS_HRES_COARSE].seq + 1);
+ WRITE_ONCE(vd[CS_RAW].seq, vd[CS_RAW].seq + 1);
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __VDSO_HELPERS_H */

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