On Fri, May 8, 2020 at 8:04 PM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
>
> When running as guest, enumerating feature split lock detection through
> CPU model is not easy since CPU model is configurable by host VMM.
>
> If running upon KVM, it can be enumerated through
> KVM_FEATURE_SPLIT_LOCK_DETECT,
This needs crystal clear documentation. What, exactly, is the host
telling the guest if it sets this flag?
> and if KVM_HINTS_SLD_FATAL is set, it
> needs to be set to sld_fatal mode.
This needs much better docs. Do you mean:
"If KVM_HINTS_SLD_FATAL is set, then the guest will get #AC if it does
a split-lock regardless of what is written to MSR_TEST_CTRL?"
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> ---
> arch/x86/include/asm/cpu.h | 2 ++
> arch/x86/kernel/cpu/intel.c | 12 ++++++++++--
> arch/x86/kernel/kvm.c | 3 +++
> 3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
> index a57f00f1d5b5..5d5b488b4b45 100644
> --- a/arch/x86/include/asm/cpu.h
> +++ b/arch/x86/include/asm/cpu.h
> @@ -42,12 +42,14 @@ unsigned int x86_model(unsigned int sig);
> unsigned int x86_stepping(unsigned int sig);
> #ifdef CONFIG_CPU_SUP_INTEL
> extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
> +extern void __init split_lock_setup(bool fatal);
> extern void switch_to_sld(unsigned long tifn);
> extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
> extern bool handle_guest_split_lock(unsigned long ip);
> extern bool split_lock_virt_switch(bool on);
> #else
> static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
> +static inline void __init split_lock_setup(bool fatal) {}
> static inline void switch_to_sld(unsigned long tifn) {}
> static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
> {
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 1e2a74e8c592..02e24134b9b5 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -996,12 +996,18 @@ static bool split_lock_verify_msr(bool on)
> return ctrl == tmp;
> }
>
> -static void __init split_lock_setup(void)
> +void __init split_lock_setup(bool fatal)
> {
> enum split_lock_detect_state state = sld_warn;
> char arg[20];
> int i, ret;
>
> + if (fatal) {
> + state = sld_fatal;
> + pr_info("forced on, sending SIGBUS on user-space split_locks\n");
> + goto set_cap;
> + }
> +
> if (!split_lock_verify_msr(false)) {
> pr_info("MSR access failed: Disabled\n");
> return;
> @@ -1037,6 +1043,7 @@ static void __init split_lock_setup(void)
> return;
> }
>
> +set_cap:
> setup_force_cpu_cap(X86_FEATURE_SPLIT_LOCK_DETECT);
> if (state == sld_fatal)
> setup_force_cpu_cap(X86_FEATURE_SLD_FATAL);
> @@ -1161,6 +1168,7 @@ void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c)
> const struct x86_cpu_id *m;
> u64 ia32_core_caps;
>
> + /* Note, paravirt support can enable SLD, e.g., see kvm_guest_init(). */
> if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
> return;
>
> @@ -1182,5 +1190,5 @@ void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c)
> return;
> }
>
> - split_lock_setup();
> + split_lock_setup(false);
> }
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 6efe0410fb72..489ea89e2e8e 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -670,6 +670,9 @@ static void __init kvm_guest_init(void)
> * overcommitted.
> */
> hardlockup_detector_disable();
> +
> + if (kvm_para_has_feature(KVM_FEATURE_SPLIT_LOCK_DETECT))
> + split_lock_setup(kvm_para_has_hint(KVM_HINTS_SLD_FATAL));
> }
>
> static noinline uint32_t __kvm_cpuid_base(void)
> --
> 2.18.2
>
