linux-kernel - [tip:timers/vdso] arm64: Fix __arch_get_hw

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Date:   Wed, 26 Jun 2019 05:38:14 -0700
From:   tip-bot for Vincenzo Frascino <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     will.deacon@....com, vincenzo.frascino@....com,
        catalin.marinas@....com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, hpa@...or.com, tglx@...utronix.de
Subject: [tip:timers/vdso] arm64: Fix __arch_get_hw_counter() implementation

Commit-ID:  27e11a9fe2e2e7e0d13f854e89a71e488678fb17
Gitweb:     https://git.kernel.org/tip/27e11a9fe2e2e7e0d13f854e89a71e488678fb17
Author:     Vincenzo Frascino <vincenzo.frascino@....com>
AuthorDate: Tue, 25 Jun 2019 17:18:03 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 26 Jun 2019 14:26:54 +0200

arm64: 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@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-arch@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-mips@...r.kernel.org
Cc: linux-kselftest@...r.kernel.org
Cc: catalin.marinas@....com
Cc: will.deacon@....com
Cc: arnd@...db.de
Cc: linux@...linux.org.uk
Cc: ralf@...ux-mips.org
Cc: paul.burton@...s.com
Cc: daniel.lezcano@...aro.org
Cc: salyzyn@...roid.com
Cc: pcc@...gle.com
Cc: shuah@...nel.org
Cc: 0x7f454c46@...il.com
Cc: linux@...musvillemoes.dk
Cc: huw@...eweavers.com
Cc: sthotton@...vell.com
Cc: andre.przywara@....com
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Link: https://lkml.kernel.org/r/20190625161804.38713-2-vincenzo.frascino@arm.com

---
 arch/arm64/include/asm/vdso/gettimeofday.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h
index 447ef417de45..b08f476b72b4 100644
--- a/arch/arm64/include/asm/vdso/gettimeofday.h
+++ b/arch/arm64/include/asm/vdso/gettimeofday.h
@@ -10,6 +10,8 @@
 #include <asm/unistd.h>
 #include <uapi/linux/time.h>
 
+#define __VDSO_USE_SYSCALL		ULLONG_MAX
+
 #define VDSO_HAS_CLOCK_GETRES		1
 
 static __always_inline
@@ -68,7 +70,24 @@ 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("mrs %0, cntvct_el0" : "=r" (res) :: "memory");
+	/*
+	 * This isb() is required to prevent that the seq lock is
+	 * speculated.#
+	 */
+	isb();
 
 	return res;
 }