Messages in this thread Patch in this message | | | Date | Wed, 22 Jan 2020 17:23:17 -0800 | From | "Luck, Tony" <> | Subject | Re: [PATCH v12] x86/split_lock: Enable split lock detection by kernel |
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On Wed, Jan 22, 2020 at 07:45:08PM -0500, Arvind Sankar wrote: > On Wed, Jan 22, 2020 at 11:24:34PM +0000, Luck, Tony wrote: > > >> +static enum split_lock_detect_state sld_state = sld_warn; > > >> + > > > > > > This sets sld_state to sld_warn even on CPUs that don't support > > > split-lock detection. split_lock_init will then try to read/write the > > > MSR to turn it on. Would it be better to initialize it to sld_off and > > > set it to sld_warn in split_lock_setup instead, which is only called if > > > the CPU supports the feature? > > > > I've lost some bits of this patch series somewhere along the way :-( There > > was once code to decide whether the feature was supported (either with > > x86_match_cpu() for a couple of models, or using the architectural test > > based on some MSR bits. I need to dig that out and put it back in. Then > > stuff can check X86_FEATURE_SPLIT_LOCK before wandering into code > > that messes with MSRs > > That code is still there (cpu_set_core_cap_bits). The issue is that with > the initialization here, nothing ever sets sld_state to sld_off if the > feature isn't supported. > > v10 had a corresponding split_lock_detect_enabled that was > 0-initialized, but Peter's patch as he sent out had the flag initialized > to sld_warn.
Ah yes. Maybe the problem is that split_lock_init() is only called on systems that support split loc detect, while we call split_lock_init() unconditionally.
What if we start with sld_state = sld_off, and then have split_lock_setup set it to either sld_warn, or whatever the user chose on the command line. Patch below (on top of patch so you can see what I'm saying, but will just merge it in for next version.
-Tony
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 7478bebcd735..b6046ccfa372 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -39,7 +39,13 @@ enum split_lock_detect_state { sld_fatal, }; -static enum split_lock_detect_state sld_state = sld_warn; +/* + * Default to sld_off because most systems do not support + * split lock detection. split_lock_setup() will switch this + * to sld_warn, and then check to see if there is a command + * line override. + */ +static enum split_lock_detect_state sld_state = sld_off; /* * Just in case our CPU detection goes bad, or you have a weird system, @@ -1017,10 +1023,11 @@ static inline bool match_option(const char *arg, int arglen, const char *opt) static void __init split_lock_setup(void) { - enum split_lock_detect_state sld = sld_state; + enum split_lock_detect_state sld; char arg[20]; int i, ret; + sld_state = sld = sld_warn; setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT); ret = cmdline_find_option(boot_command_line, "split_lock_ac",
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