From: Fenghua Yu <fenghua.yu@intel.com>
To: "Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@elte.hu>,
"H. Peter Anvin" <hpa@linux.intel.com>,
"Ashok Raj" <ashok.raj@intel.com>,
"Ravi V Shankar" <ravi.v.shankar@intel.com>,
"Tony Luck" <tony.luck@intel.com>,
"Dave Hansen" <dave.hansen@intel.com>,
"Rafael Wysocki" <rafael.j.wysocki@intel.com>,
"Arjan van de Ven" <arjan@infradead.org>,
"Alan Cox" <alan@linux.intel.com>
Cc: "x86" <x86@kernel.org>,
"linux-kernel" <linux-kernel@vger.kernel.org>,
Fenghua Yu <fenghua.yu@intel.com>
Subject: [PATCH 05/15] x86/split_lock: Use non atomic set and clear bit instructions to clear cpufeature
Date: Mon, 14 May 2018 11:52:15 -0700 [thread overview]
Message-ID: <1526323945-211107-6-git-send-email-fenghua.yu@intel.com> (raw)
In-Reply-To: <1526323945-211107-1-git-send-email-fenghua.yu@intel.com>
When #AC exception is enabled for split locked accesses,
clear_cpufeature() generates #AC exception because of atomic setting
or clearing bits in non cache line aligned x86_capability depending
on compiler.
But kernel clears cpufeatures only when a CPU boots up. Therefore, there
is no racing condition when clear_cpufeature() is called and no need to
atomically clear or set x86_capability.
To avoid #AC exception caused by split lock and get better performance,
call non atomic __set_bit() and __clear_bit().
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
arch/x86/kernel/cpu/cpuid-deps.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 2c0bd38a44ab..0c02c6e44ea7 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -65,15 +65,15 @@ static const struct cpuid_dep cpuid_deps[] = {
static inline void clear_feature(struct cpuinfo_x86 *c, unsigned int feature)
{
/*
- * Note: This could use the non atomic __*_bit() variants, but the
- * rest of the cpufeature code uses atomics as well, so keep it for
- * consistency. Cleanup all of it separately.
+ * Because this code is only called during boot time and there
+ * is no need to be atomic, use non atomic __*_bit() to avoid
+ * #AC exception for split locked access.
*/
if (!c) {
clear_cpu_cap(&boot_cpu_data, feature);
- set_bit(feature, (unsigned long *)cpu_caps_cleared);
+ __set_bit(feature, (unsigned long *)cpu_caps_cleared);
} else {
- clear_bit(feature, (unsigned long *)c->x86_capability);
+ __clear_bit(feature, (unsigned long *)c->x86_capability);
}
}
--
2.5.0
next prev parent reply other threads:[~2018-05-14 18:54 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-14 18:52 [PATCH 0/15] x86/split_lock: Enable #AC exception for split locked accesses Fenghua Yu
2018-05-14 18:52 ` [PATCH 01/15] x86/split_lock: Add CONFIG and enumerate #AC exception for split locked access feature Fenghua Yu
2018-05-15 15:36 ` Dave Hansen
2018-05-15 15:41 ` Fenghua Yu
2018-05-15 15:54 ` Dave Hansen
2018-05-14 18:52 ` [PATCH 02/15] x86/split_lock: Set up #AC exception for split locked accesses Fenghua Yu
2018-05-14 18:52 ` [PATCH 03/15] x86/split_lock: Handle #AC exception for split lock in kernel mode Fenghua Yu
2018-05-15 15:51 ` Dave Hansen
2018-05-15 16:35 ` Luck, Tony
2018-05-15 17:21 ` Fenghua Yu
2018-05-16 16:44 ` Dave Hansen
2018-05-16 21:35 ` Fenghua Yu
2018-05-14 18:52 ` [PATCH 04/15] x86/split_lock: Use non locked bit set instruction in set_cpu_cap Fenghua Yu
2018-05-14 18:52 ` Fenghua Yu [this message]
2018-05-14 18:52 ` [PATCH 06/15] x86/split_lock: Save #AC setting for split lock in BIOS in boot time and restore the setting in reboot Fenghua Yu
2018-05-14 18:52 ` [PATCH 07/15] x86/split_lock: Handle suspend/hibernate and resume Fenghua Yu
2018-05-14 21:42 ` Rafael J. Wysocki
2018-05-14 18:52 ` [PATCH 08/15] x86/split_lock: Set split lock during EFI runtime service Fenghua Yu
2018-05-14 18:52 ` [PATCH 09/15] x86/split_lock: Explicitly enable or disable #AC for split locked accesses Fenghua Yu
2018-05-15 16:15 ` Dave Hansen
2018-05-15 17:29 ` Fenghua Yu
2018-05-16 16:37 ` Dave Hansen
2018-05-14 18:52 ` [PATCH 10/15] x86/split_lock: Add a sysfs interface to allow user to enable or disable split lock during run time Fenghua Yu
2018-05-14 18:52 ` [PATCH 11/15] x86/split_lock: Add sysfs interface to control user mode behavior Fenghua Yu
2018-05-14 18:52 ` [PATCH 12/15] x86/split_lock: Add sysfs interface to show and control BIOS split lock setting Fenghua Yu
2018-05-14 18:52 ` [PATCH 13/15] x86/split_lock: Trace #AC exception for split lock Fenghua Yu
2018-05-14 18:52 ` [PATCH 14/15] x86/split_lock: Add CONFIG and testing sysfs interface Fenghua Yu
2018-05-14 18:52 ` [PATCH 15/15] x86/split_lock: Add split lock user space test in selftest Fenghua Yu
2018-05-15 15:10 ` [PATCH 0/15] x86/split_lock: Enable #AC exception for split locked accesses Dave Hansen
2018-05-15 16:26 ` Alan Cox
2018-05-15 16:30 ` Dave Hansen
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