Messages in this thread | | | Subject | Re: [PATCH v5 1/9] x86/split_lock: Rework the initialization flow of split lock detection | From | Xiaoyao Li <> | Date | Tue, 24 Mar 2020 09:10:55 +0800 |
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On 3/24/2020 4:24 AM, Thomas Gleixner wrote: > Thomas Gleixner <tglx@linutronix.de> writes: >> Xiaoyao Li <xiaoyao.li@intel.com> writes: >> >>> Current initialization flow of split lock detection has following issues: >>> 1. It assumes the initial value of MSR_TEST_CTRL.SPLIT_LOCK_DETECT to be >>> zero. However, it's possible that BIOS/firmware has set it. >> >> Ok. >> >>> 2. X86_FEATURE_SPLIT_LOCK_DETECT flag is unconditionally set even if >>> there is a virtualization flaw that FMS indicates the existence while >>> it's actually not supported. >>> >>> 3. Because of #2, KVM cannot rely on X86_FEATURE_SPLIT_LOCK_DETECT flag >>> to check verify if feature does exist, so cannot expose it to >>> guest. >> >> Sorry this does not make anny sense. KVM is the hypervisor, so it better >> can rely on the detect flag. Unless you talk about nested virt and a >> broken L1 hypervisor. >> >>> To solve these issues, introducing a new sld_state, "sld_not_exist", >>> as >> >> The usual naming convention is sld_not_supported. > > But this extra state is not needed at all, it already exists: > > X86_FEATURE_SPLIT_LOCK_DETECT > > You just need to make split_lock_setup() a bit smarter. Soemthing like > the below. It just wants to be split into separate patches. > > Thanks, > > tglx > --- > --- a/arch/x86/kernel/cpu/intel.c > +++ b/arch/x86/kernel/cpu/intel.c > @@ -45,6 +45,7 @@ enum split_lock_detect_state { > * split lock detect, unless there is a command line override. > */ > static enum split_lock_detect_state sld_state = sld_off; > +static DEFINE_PER_CPU(u64, msr_test_ctrl_cache);
I used percpu cache in v3, but people prefer Tony's cache for reserved bits[1].
If you prefer percpu cache, I'll use it in next version.
[1]: https://lore.kernel.org/lkml/20200303192242.GU1439@linux.intel.com/
> /* > * Processors which have self-snooping capability can handle conflicting > @@ -984,11 +985,32 @@ static inline bool match_option(const ch > return len == arglen && !strncmp(arg, opt, len); > } > > +static bool __init split_lock_verify_msr(bool on) > +{ > + u64 ctrl, tmp; > + > + if (rdmsrl_safe(MSR_TEST_CTRL, &ctrl)) > + return false; > + if (on) > + ctrl |= MSR_TEST_CTRL_SPLIT_LOCK_DETECT; > + else > + ctrl &= ~MSR_TEST_CTRL_SPLIT_LOCK_DETECT; > + if (wrmsrl_safe(MSR_TEST_CTRL, ctrl)) > + return false; > + rdmsrl(MSR_TEST_CTRL, tmp); > + return ctrl == tmp; > +} > + > static void __init split_lock_setup(void) > { > char arg[20]; > int i, ret; > > + if (!split_lock_verify_msr(true) || !split_lock_verify_msr(false)) { > + pr_info("MSR access failed: Disabled\n"); > + return; > + } > +
I did similar thing like this in my v3, however Sean raised concern that toggling MSR bit before parsing kernel param is bad behavior. [2]
[2]: https://lore.kernel.org/kvm/20200305162311.GG11500@linux.intel.com/
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