| Message ID | 20231101183032.1498211-1-paul@xen.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v4] KVM x86/xen: add an override for PVCLOCK_TSC_STABLE_BIT | expand |
Hi Paul, kernel test robot noticed the following build warnings: [auto build test WARNING on 35dcbd9e47035f98f3910ae420bf10892c9bdc99] url: https://github.com/intel-lab-lkp/linux/commits/Paul-Durrant/KVM-x86-xen-add-an-override-for-PVCLOCK_TSC_STABLE_BIT/20231102-034122 base: 35dcbd9e47035f98f3910ae420bf10892c9bdc99 patch link: https://lore.kernel.org/r/20231101183032.1498211-1-paul%40xen.org patch subject: [PATCH v4] KVM x86/xen: add an override for PVCLOCK_TSC_STABLE_BIT config: i386-randconfig-013-20231102 (https://download.01.org/0day-ci/archive/20231102/202311021159.ppYESBYx-lkp@intel.com/config) compiler: gcc-12 (Debian 12.2.0-14) 12.2.0 reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231102/202311021159.ppYESBYx-lkp@intel.com/reproduce) If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags | Reported-by: kernel test robot <lkp@intel.com> | Closes: https://lore.kernel.org/oe-kbuild-all/202311021159.ppYESBYx-lkp@intel.com/ All warnings (new ones prefixed by >>): arch/x86/kvm/x86.c: In function 'kvm_guest_time_update': >> arch/x86/kvm/x86.c:3176:14: warning: unused variable 'xen_pvclock_tsc_unstable' [-Wunused-variable] 3176 | bool xen_pvclock_tsc_unstable = | ^~~~~~~~~~~~~~~~~~~~~~~~ vim +/xen_pvclock_tsc_unstable +3176 arch/x86/kvm/x86.c 3158 3159 static int kvm_guest_time_update(struct kvm_vcpu *v) 3160 { 3161 unsigned long flags, tgt_tsc_khz; 3162 unsigned seq; 3163 struct kvm_vcpu_arch *vcpu = &v->arch; 3164 struct kvm_arch *ka = &v->kvm->arch; 3165 s64 kernel_ns; 3166 u64 tsc_timestamp, host_tsc; 3167 u8 pvclock_flags; 3168 bool use_master_clock; 3169 3170 /* 3171 * For Xen guests we may need to override PVCLOCK_TSC_STABLE_BIT as unless 3172 * explicitly told to use TSC as its clocksource Xen will not set this bit. 3173 * This default behaviour led to bugs in some guest kernels which cause 3174 * problems if they observe PVCLOCK_TSC_STABLE_BIT in the pvclock flags. 3175 */ > 3176 bool xen_pvclock_tsc_unstable = 3177 ka->xen_hvm_config.flags & KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE; 3178 3179 kernel_ns = 0; 3180 host_tsc = 0; 3181 3182 /* 3183 * If the host uses TSC clock, then passthrough TSC as stable 3184 * to the guest. 3185 */ 3186 do { 3187 seq = read_seqcount_begin(&ka->pvclock_sc); 3188 use_master_clock = ka->use_master_clock; 3189 if (use_master_clock) { 3190 host_tsc = ka->master_cycle_now; 3191 kernel_ns = ka->master_kernel_ns; 3192 } 3193 } while (read_seqcount_retry(&ka->pvclock_sc, seq)); 3194 3195 /* Keep irq disabled to prevent changes to the clock */ 3196 local_irq_save(flags); 3197 tgt_tsc_khz = get_cpu_tsc_khz(); 3198 if (unlikely(tgt_tsc_khz == 0)) { 3199 local_irq_restore(flags); 3200 kvm_make_request(KVM_REQ_CLOCK_UPDATE, v); 3201 return 1; 3202 } 3203 if (!use_master_clock) { 3204 host_tsc = rdtsc(); 3205 kernel_ns = get_kvmclock_base_ns(); 3206 } 3207 3208 tsc_timestamp = kvm_read_l1_tsc(v, host_tsc); 3209 3210 /* 3211 * We may have to catch up the TSC to match elapsed wall clock 3212 * time for two reasons, even if kvmclock is used. 3213 * 1) CPU could have been running below the maximum TSC rate 3214 * 2) Broken TSC compensation resets the base at each VCPU 3215 * entry to avoid unknown leaps of TSC even when running 3216 * again on the same CPU. This may cause apparent elapsed 3217 * time to disappear, and the guest to stand still or run 3218 * very slowly. 3219 */ 3220 if (vcpu->tsc_catchup) { 3221 u64 tsc = compute_guest_tsc(v, kernel_ns); 3222 if (tsc > tsc_timestamp) { 3223 adjust_tsc_offset_guest(v, tsc - tsc_timestamp); 3224 tsc_timestamp = tsc; 3225 } 3226 } 3227 3228 local_irq_restore(flags); 3229 3230 /* With all the info we got, fill in the values */ 3231 3232 if (kvm_caps.has_tsc_control) 3233 tgt_tsc_khz = kvm_scale_tsc(tgt_tsc_khz, 3234 v->arch.l1_tsc_scaling_ratio); 3235 3236 if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) { 3237 kvm_get_time_scale(NSEC_PER_SEC, tgt_tsc_khz * 1000LL, 3238 &vcpu->hv_clock.tsc_shift, 3239 &vcpu->hv_clock.tsc_to_system_mul); 3240 vcpu->hw_tsc_khz = tgt_tsc_khz; 3241 kvm_xen_update_tsc_info(v); 3242 } 3243 3244 vcpu->hv_clock.tsc_timestamp = tsc_timestamp; 3245 vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; 3246 vcpu->last_guest_tsc = tsc_timestamp; 3247 3248 /* If the host uses TSC clocksource, then it is stable */ 3249 pvclock_flags = 0; 3250 if (use_master_clock) 3251 pvclock_flags |= PVCLOCK_TSC_STABLE_BIT; 3252 3253 vcpu->hv_clock.flags = pvclock_flags; 3254 3255 if (vcpu->pv_time.active) 3256 kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0, false); 3257 #ifdef CONFIG_KVM_XEN 3258 if (vcpu->xen.vcpu_info_cache.active) 3259 kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache, 3260 offsetof(struct compat_vcpu_info, time), 3261 xen_pvclock_tsc_unstable); 3262 if (vcpu->xen.vcpu_time_info_cache.active) 3263 kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0, 3264 xen_pvclock_tsc_unstable); 3265 #endif 3266 kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); 3267 return 0; 3268 } 3269
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 67347d827242..880b929a5cb1 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8270,6 +8270,7 @@ PVHVM guests. Valid flags are:: #define KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL (1 << 4) #define KVM_XEN_HVM_CONFIG_EVTCHN_SEND (1 << 5) #define KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG (1 << 6) + #define KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE (1 << 7) The KVM_XEN_HVM_CONFIG_HYPERCALL_MSR flag indicates that the KVM_XEN_HVM_CONFIG ioctl is available, for the guest to set its hypercall page. @@ -8313,6 +8314,11 @@ behave more correctly, not using the XEN_RUNSTATE_UPDATE flag until/unless specifically enabled (by the guest making the hypercall, causing the VMM to enable the KVM_XEN_ATTR_TYPE_RUNSTATE_UPDATE_FLAG attribute). +The KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE flag indicates that KVM supports +clearing the PVCLOCK_TSC_STABLE_BIT flag in Xen pvclock sources. This will be +done when the KVM_CAP_XEN_HVM ioctl sets the +KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE flag. + 8.31 KVM_CAP_PPC_MULTITCE ------------------------- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2c924075f6f1..e43449382cba 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3104,7 +3104,8 @@ u64 get_kvmclock_ns(struct kvm *kvm) static void kvm_setup_guest_pvclock(struct kvm_vcpu *v, struct gfn_to_pfn_cache *gpc, - unsigned int offset) + unsigned int offset, + bool force_tsc_unstable) { struct kvm_vcpu_arch *vcpu = &v->arch; struct pvclock_vcpu_time_info *guest_hv_clock; @@ -3141,6 +3142,10 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v, } memcpy(guest_hv_clock, &vcpu->hv_clock, sizeof(*guest_hv_clock)); + + if (force_tsc_unstable) + guest_hv_clock->flags &= ~PVCLOCK_TSC_STABLE_BIT; + smp_wmb(); guest_hv_clock->version = ++vcpu->hv_clock.version; @@ -3162,6 +3167,15 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) u8 pvclock_flags; bool use_master_clock; + /* + * For Xen guests we may need to override PVCLOCK_TSC_STABLE_BIT as unless + * explicitly told to use TSC as its clocksource Xen will not set this bit. + * This default behaviour led to bugs in some guest kernels which cause + * problems if they observe PVCLOCK_TSC_STABLE_BIT in the pvclock flags. + */ + bool xen_pvclock_tsc_unstable = + ka->xen_hvm_config.flags & KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE; + kernel_ns = 0; host_tsc = 0; @@ -3239,13 +3253,15 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) vcpu->hv_clock.flags = pvclock_flags; if (vcpu->pv_time.active) - kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0); + kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0, false); #ifdef CONFIG_KVM_XEN if (vcpu->xen.vcpu_info_cache.active) kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache, - offsetof(struct compat_vcpu_info, time)); + offsetof(struct compat_vcpu_info, time), + xen_pvclock_tsc_unstable); if (vcpu->xen.vcpu_time_info_cache.active) - kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0); + kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0, + xen_pvclock_tsc_unstable); #endif kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); return 0; @@ -4638,7 +4654,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL | KVM_XEN_HVM_CONFIG_SHARED_INFO | KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL | - KVM_XEN_HVM_CONFIG_EVTCHN_SEND; + KVM_XEN_HVM_CONFIG_EVTCHN_SEND | + KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE; if (sched_info_on()) r |= KVM_XEN_HVM_CONFIG_RUNSTATE | KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG; diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index e53fad915a62..e43948b87f94 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1162,7 +1162,9 @@ int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc) { /* Only some feature flags need to be *enabled* by userspace */ u32 permitted_flags = KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL | - KVM_XEN_HVM_CONFIG_EVTCHN_SEND; + KVM_XEN_HVM_CONFIG_EVTCHN_SEND | + KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE; + u32 old_flags; if (xhc->flags & ~permitted_flags) return -EINVAL; @@ -1183,9 +1185,14 @@ int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc) else if (!xhc->msr && kvm->arch.xen_hvm_config.msr) static_branch_slow_dec_deferred(&kvm_xen_enabled); + old_flags = kvm->arch.xen_hvm_config.flags; memcpy(&kvm->arch.xen_hvm_config, xhc, sizeof(*xhc)); mutex_unlock(&kvm->arch.xen.xen_lock); + + if ((old_flags ^ xhc->flags) & KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE) + kvm_make_all_cpus_request(kvm, KVM_REQ_CLOCK_UPDATE); + return 0; } diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 13065dd96132..e21b53e8358d 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1282,6 +1282,7 @@ struct kvm_x86_mce { #define KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL (1 << 4) #define KVM_XEN_HVM_CONFIG_EVTCHN_SEND (1 << 5) #define KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG (1 << 6) +#define KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE (1 << 7) struct kvm_xen_hvm_config { __u32 flags;