From: Fenghua Yu <fenghua.yu@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
H Peter Anvin <hpa@zytor.com>,
Dave Hansen <dave.hansen@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Ashok Raj <ashok.raj@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Kalle Valo <kvalo@codeaurora.org>,
Xiaoyao Li <xiaoyao.li@intel.com>,
Michael Chan <michael.chan@broadcom.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>,
linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
kvm@vger.kernel.org
Subject: Re: [PATCH v6 13/20] x86/split_lock: Enable split lock detection by default
Date: Thu, 4 Apr 2019 12:23:07 -0700 [thread overview]
Message-ID: <20190404192306.GA178488@romley-ivt3.sc.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1904041932500.1802@nanos.tec.linutronix.de>
On Thu, Apr 04, 2019 at 08:07:57PM +0200, Thomas Gleixner wrote:
> On Wed, 3 Apr 2019, Fenghua Yu wrote:
>
> > A split locked access locks bus and degrades overall memory access
> > performance. When split lock detection feature is enumerated, enable
> > the feature by default to find any split lock issue and then fix
> > the issue.
>
> Enabling the feature allows to find the issues, but does not automagically
> fix them. Come on.
Ok. I will remove the "and then fix the issue".
>
> > +#define DISABLE_SPLIT_LOCK_DETECT 0
> > +#define ENABLE_SPLIT_LOCK_DETECT 1
>
> If those defines have a value at all, please start with the facility not
> with functionality, i.e. AC_SPLIT_LOCK_ENABLE....
OK.
>
> > +
> > +static DEFINE_MUTEX(split_lock_detect_mutex);
> > +static int split_lock_detect_val;
>
> detect_val? What value is that?
According to previous discussions, I was told to call this split lock feature
as "split lock detection" instead of "#AC for split lock". So I use
"split_lock_detect..." in variable names or function names, call feature flag
as "split_lock_detect", and call the feature as "split lock detection" in
descriptions.
If you don't agree to name feature as "split lock detection", I can change
variable names/function names/feature flag/descriptions etc back to previous
names "ac_split_lock...", "#AC for split lock", etc.
The variable split_lock_detect_val is either 0 or 1. It stores current
enable/disable status of split lock detection feature. By default it's
one after the feature is enumerated. Then sysadmin can change it to 0 or 1
to enable or disable the feature during run time.
> Its supposed to hold those magic defines
> above. So something like
>
> static unsigned int ac_split_lock_enable;
If you agree to name the split lock feature as "split lock detection" feature,
can I change this variable to static unsigned int split_lock_detect_enable?
> > /*
> > * Just in case our CPU detection goes bad, or you have a weird system,
> > * allow a way to override the automatic disabling of MPX.
> > @@ -161,10 +167,45 @@ static bool bad_spectre_microcode(struct cpuinfo_x86 *c)
> > return false;
> > }
> >
> > +static u32 new_sp_test_ctl_val(u32 test_ctl_val)
> > +{
> > + /* Change the split lock setting. */
> > + if (READ_ONCE(split_lock_detect_val) == DISABLE_SPLIT_LOCK_DETECT)
>
> That READ_ONCE() is required because?
Ok. Will remove READ_ONCE().
>
> > + test_ctl_val &= ~TEST_CTL_ENABLE_SPLIT_LOCK_DETECT;
> > + else
> > + test_ctl_val |= TEST_CTL_ENABLE_SPLIT_LOCK_DETECT;
> > +
> > + return test_ctl_val;
> > +}
>
> Aside of that do we really need a misnomed function which replaces the
> simple inline code at the call site:
>
> rdmsr(l, h)
> l &= ~TEST_CTL_ENABLE_SPLIT_LOCK_DETECT;
> l |= ac_split_lock_enable << TEST_CTL_ENABLE_SPLIT_LOCK_DETECT_SHIFT;
> wrmrs(...)
>
> or the even more simple
>
> if (ac_split_lock_enable)
> msr_set_bit(...)
> else
> msr_clear_nit(...)
>
> Hmm?
The function new_sp_test_ctrl_val() will be called twice: here when
initializing split lock detection and in split_lock_detect_store()
when enabling/disabling the feature through the sysfs interface in
patch 0014.
So can I still keep this function and name it as get_new_test_ctrl_val()?
>
> > +
> > +static inline void show_split_lock_detection_info(void)
> > +{
> > + if (READ_ONCE(split_lock_detect_val))
>
> That READ_ONCE() is required because?
Ok. Will remove READ_ONCE().
>
> > + pr_info_once("x86/split_lock: split lock detection enabled\n");
> > + else
> > + pr_info_once("x86/split_lock: split lock detection disabled\n");
>
> pr_fmt exists for a reason and having 'split lock' repeated several times
> in the same line is not making it more readable.
Ok. I will change the string to "x86/split_lock_detection: enabled\n",
is it ok?
>
>
> > +
> > /* Unmask CPUID levels if masked: */
> > if (c->x86 > 6 || (c->x86 == 6 && c->x86_model >= 0xd)) {
> > if (msr_clear_bit(MSR_IA32_MISC_ENABLE,
> > @@ -1032,6 +1073,7 @@ cpu_dev_register(intel_cpu_dev);
> > static void __init set_split_lock_detect(void)
> > {
> > setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
> > + split_lock_detect_val = 1;
>
> Oh well. You add defines on top of the file and then you don't use them.
Will fix this.
Thanks.
-Fenghua
next prev parent reply other threads:[~2019-04-04 19:30 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-03 21:21 [PATCH v6 00/20] x86/split_lock: Enable split locked accesses detection Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 01/20] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long Fenghua Yu
2019-04-04 14:39 ` Borislav Petkov
2019-04-04 15:54 ` Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 02/20] drivers/net/b44: Align pwol_mask to unsigned long for better performance Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 03/20] wlcore: simplify/fix/optimize reg_ch_conf_pending operations Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 04/20] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access Fenghua Yu
2019-04-04 14:44 ` David Laight
2019-04-04 16:24 ` David Laight
2019-04-04 16:35 ` Sean Christopherson
2019-04-04 16:52 ` Thomas Gleixner
2019-04-04 17:29 ` Paolo Bonzini
2019-04-04 18:11 ` Thomas Gleixner
2019-04-05 9:23 ` David Laight
2019-04-03 21:21 ` [PATCH v6 05/20] x86/msr-index: Define MSR_IA32_CORE_CAPABILITY and split lock detection bit Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 06/20] x86/cpufeatures: Enumerate MSR_IA32_CORE_CAPABILITY Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 07/20] x86/split_lock: Enumerate split lock detection by MSR_IA32_CORE_CAPABILITY Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 08/20] x86/split_lock: Enumerate split lock detection on Icelake mobile processor Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 09/20] x86/split_lock: Define MSR_TEST_CTL register Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 10/20] x86/split_lock: Handle #AC exception for split lock Fenghua Yu
2019-04-04 17:31 ` Thomas Gleixner
2019-04-04 22:49 ` Fenghua Yu
2019-04-03 21:21 ` [PATCH v6 11/20] kvm/x86: Emulate MSR IA32_CORE_CAPABILITY Fenghua Yu
2019-04-05 12:00 ` Thomas Gleixner
2019-04-09 6:03 ` Xiaoyao Li
2019-04-03 21:21 ` [PATCH v6 12/20] kvm/vmx: Emulate MSR TEST_CTL Fenghua Yu
2019-04-04 14:44 ` Sean Christopherson
2019-04-08 8:54 ` Xiaoyao Li
2019-04-05 12:30 ` Thomas Gleixner
2019-04-08 9:54 ` Xiaoyao Li
2019-04-08 17:48 ` Sean Christopherson
2019-04-10 5:03 ` Xiaoyao Li
2019-04-03 21:21 ` [PATCH v6 13/20] x86/split_lock: Enable split lock detection by default Fenghua Yu
2019-04-04 18:07 ` Thomas Gleixner
2019-04-04 18:14 ` Thomas Gleixner
2019-04-04 19:23 ` Fenghua Yu [this message]
2019-04-04 19:44 ` Thomas Gleixner
2019-04-10 0:02 ` Fenghua Yu
2019-04-10 6:31 ` Thomas Gleixner
2019-04-10 12:35 ` Fenghua Yu
2019-04-10 8:50 ` David Laight
2019-04-03 21:22 ` [PATCH v6 14/20] x86/split_lock: Add a sysfs interface to enable/disable split lock detection during run time Fenghua Yu
2019-04-04 19:11 ` Thomas Gleixner
2019-04-03 21:22 ` [PATCH v6 15/20] x86/split_lock: Document the new sysfs file for split lock detection Fenghua Yu
2019-04-03 21:22 ` [PATCH v6 16/20] x86/clearcpuid: Support multiple clearcpuid options Fenghua Yu
2019-04-03 21:22 ` [PATCH v6 17/20] x86/clearcpuid: Support feature flag string in kernel option clearcpuid Fenghua Yu
2019-04-03 21:22 ` [PATCH v6 18/20] x86/clearcpuid: Apply cleared feature bits that are forced set before Fenghua Yu
2019-04-03 21:22 ` [PATCH v6 19/20] x86/clearcpuid: Clear CPUID bit in CPUID faulting Fenghua Yu
2019-04-03 21:22 ` [PATCH v6 20/20] x86/clearcpuid: Change document for kernel option clearcpuid Fenghua Yu
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