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@xxxxxxxxx/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@xxxxxxxxx/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@xxxxxxxxx> | Closes: https://lore.kernel.org/oe-kbuild-all/202311021159.ppYESBYx-lkp@xxxxxxxxx/ 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 -- 0-DAY CI Kernel Test Service https://github.com/intel/lkp-tests/wiki
