lkml.org 
[lkml]   [2019]   [Jun]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:timers/vdso] arm64: compat: Fix __arch_get_hw_counter() implementation
Commit-ID:  6241c4dc6ec56a7627b972959da8b492b765b209
Gitweb: https://git.kernel.org/tip/6241c4dc6ec56a7627b972959da8b492b765b209
Author: Vincenzo Frascino <vincenzo.frascino@arm.com>
AuthorDate: Tue, 25 Jun 2019 17:18:04 +0100
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 26 Jun 2019 14:26:54 +0200

arm64: compat: Fix __arch_get_hw_counter() implementation

Provide the following fixes for the __arch_get_hw_counter()
implementation on arm64:
- Fallback on syscall when an unstable counter is detected.
- Introduce isb()s before and after the counter read to avoid
speculation of the counter value and of the seq lock
respectively.
The second isb() is a temporary solution that will be revisited
in 5.3-rc1.

These fixes restore the semantics that __arch_counter_get_cntvct()
had on arm64.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@arm.com
Cc: will.deacon@arm.com
Cc: arnd@arndb.de
Cc: linux@armlinux.org.uk
Cc: ralf@linux-mips.org
Cc: paul.burton@mips.com
Cc: daniel.lezcano@linaro.org
Cc: salyzyn@android.com
Cc: pcc@google.com
Cc: shuah@kernel.org
Cc: 0x7f454c46@gmail.com
Cc: linux@rasmusvillemoes.dk
Cc: huw@codeweavers.com
Cc: sthotton@marvell.com
Cc: andre.przywara@arm.com
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190625161804.38713-3-vincenzo.frascino@arm.com

---
arch/arm64/include/asm/vdso/compat_gettimeofday.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/arch/arm64/include/asm/vdso/compat_gettimeofday.h b/arch/arm64/include/asm/vdso/compat_gettimeofday.h
index 93dbd935b66d..f4812777f5c5 100644
--- a/arch/arm64/include/asm/vdso/compat_gettimeofday.h
+++ b/arch/arm64/include/asm/vdso/compat_gettimeofday.h
@@ -12,6 +12,8 @@

#include <asm/vdso/compat_barrier.h>

+#define __VDSO_USE_SYSCALL ULLONG_MAX
+
#define VDSO_HAS_CLOCK_GETRES 1

static __always_inline
@@ -74,8 +76,24 @@ static __always_inline u64 __arch_get_hw_counter(s32 clock_mode)
{
u64 res;

+ /*
+ * clock_mode == 0 implies that vDSO are enabled otherwise
+ * fallback on syscall.
+ */
+ if (clock_mode)
+ return __VDSO_USE_SYSCALL;
+
+ /*
+ * This isb() is required to prevent that the counter value
+ * is speculated.
+ */
isb();
asm volatile("mrrc p15, 1, %Q0, %R0, c14" : "=r" (res));
+ /*
+ * This isb() is required to prevent that the seq lock is
+ * speculated.
+ */
+ isb();

return res;
}
\
 
 \ /
  Last update: 2019-06-26 14:40    [W:0.124 / U:52.544 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site