* [sean-jc:x86/host_kvmclock_mess 14/15] arch/x86/kvm/x86.c:1875:26: warning: variable 'master_ns' is uninitialized when used here
@ 2026-07-30 5:10 kernel test robot
0 siblings, 0 replies; only message in thread
From: kernel test robot @ 2026-07-30 5:10 UTC (permalink / raw)
To: David Woodhouse; +Cc: llvm, oe-kbuild-all, Sean Christopherson
tree: https://github.com/sean-jc/linux x86/host_kvmclock_mess
head: 1874dce49fd558c97bf46e9d2a7e635c5158f74a
commit: a7428fb09dd20b70ce3619c430eb42e6f298a503 [14/15] KVM: x86: Upscalte TSC to "now", not master clock when updating PV clocks
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20260730/202607300751.31hStxN9-lkp@intel.com/config)
compiler: clang version 22.1.8 (https://github.com/llvm/llvm-project ca7933e47d3a3451d81e72ac174dcb5aa28b59d1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260730/202607300751.31hStxN9-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/202607300751.31hStxN9-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> arch/x86/kvm/x86.c:1875:26: warning: variable 'master_ns' is uninitialized when used here [-Wuninitialized]
1875 | hv_clock.system_time = master_ns + v->kvm->arch.kvmclock_offset;
| ^~~~~~~~~
arch/x86/kvm/x86.c:1782:64: note: initialize the variable 'master_ns' to silence this warning
1782 | u64 tgt_tsc_hz, tsc_timestamp, host_tsc, master_tsc, master_ns;
| ^
| = 0
1 warning generated.
vim +/master_ns +1875 arch/x86/kvm/x86.c
1779
1780 int kvm_guest_time_update(struct kvm_vcpu *v)
1781 {
1782 u64 tgt_tsc_hz, tsc_timestamp, host_tsc, master_tsc, master_ns;
1783 struct pvclock_vcpu_time_info hv_clock = {};
1784 struct kvm_vcpu_arch *vcpu = &v->arch;
1785 s64 kernel_ns;
1786
1787 /*
1788 * If the host uses TSC clock, then passthrough TSC as stable
1789 * to the guest.
1790 */
1791 #ifdef CONFIG_X86_64
1792 struct kvm_arch *ka = &v->kvm->arch;
1793 bool use_master_clock;
1794 unsigned seq;
1795
1796 do {
1797 seq = read_seqcount_begin(&ka->pvclock_sc);
1798 use_master_clock = ka->use_master_clock;
1799 if (!use_master_clock)
1800 continue;
1801
1802 if (!kvm_get_time_and_clockread(&kernel_ns, &host_tsc)) {
1803 use_master_clock = false;
1804 continue;
1805 }
1806
1807 master_tsc = ka->master_cycle_now;
1808 kernel_ns = ka->master_kernel_ns;
1809 } while (read_seqcount_retry(&ka->pvclock_sc, seq));
1810 #else
1811 const bool use_master_clock = false;
1812 #endif
1813 /*
1814 * Ensure reading the TSC+frequency pair is done on the same CPU. When
1815 * NOT using the master clock, the TSC frequency may vary between CPUs.
1816 */
1817 preempt_disable();
1818 tgt_tsc_hz = (u64)get_cpu_tsc_khz() * HZ_PER_KHZ;
1819 if (unlikely(tgt_tsc_hz == 0)) {
1820 preempt_enable();
1821 kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
1822 return 1;
1823 }
1824 if (!use_master_clock) {
1825 host_tsc = rdtsc();
1826 kernel_ns = get_kvmclock_base_ns();
1827 }
1828
1829 tsc_timestamp = kvm_read_l1_tsc(v, host_tsc);
1830
1831 /*
1832 * We may have to catch up the TSC to match elapsed wall clock
1833 * time for two reasons, even if kvmclock is used.
1834 * 1) CPU could have been running below the maximum TSC rate
1835 * 2) Broken TSC compensation resets the base at each VCPU
1836 * entry to avoid unknown leaps of TSC even when running
1837 * again on the same CPU. This may cause apparent elapsed
1838 * time to disappear, and the guest to stand still or run
1839 * very slowly.
1840 */
1841 if (vcpu->tsc_catchup) {
1842 u64 tsc = compute_guest_tsc(v, kernel_ns);
1843 if (tsc > tsc_timestamp) {
1844 adjust_tsc_offset_guest(v, tsc - tsc_timestamp);
1845 tsc_timestamp = tsc;
1846 }
1847 }
1848
1849 preempt_enable();
1850
1851 /* With all the info we got, fill in the values */
1852
1853 if (kvm_caps.has_tsc_control) {
1854 tgt_tsc_hz = kvm_scale_tsc(tgt_tsc_hz,
1855 v->arch.l1_tsc_scaling_ratio);
1856 tgt_tsc_hz = tgt_tsc_hz ? : 1;
1857 }
1858
1859 if (unlikely(vcpu->hw_tsc_hz != tgt_tsc_hz)) {
1860 kvm_get_time_scale(NSEC_PER_SEC, tgt_tsc_hz,
1861 &vcpu->pvclock_tsc_shift,
1862 &vcpu->pvclock_tsc_mul);
1863 vcpu->hw_tsc_hz = tgt_tsc_hz;
1864 }
1865
1866 hv_clock.tsc_shift = vcpu->pvclock_tsc_shift;
1867 hv_clock.tsc_to_system_mul = vcpu->pvclock_tsc_mul;
1868 /*
1869 * If the master clock is NOT in use, the reference time placed in the
1870 * hv_clock is "now". If master clock is in use, the reference time is
1871 * the master clock's snapshot from some time in the past, not "now".
1872 */
1873 if (use_master_clock) {
1874 hv_clock.tsc_timestamp = kvm_read_l1_tsc(v, master_tsc);
> 1875 hv_clock.system_time = master_ns + v->kvm->arch.kvmclock_offset;
1876 } else {
1877 hv_clock.tsc_timestamp = tsc_timestamp;
1878 hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset;
1879 }
1880 vcpu->last_guest_tsc = tsc_timestamp;
1881
1882 /* If the host uses TSC clocksource, then it is stable */
1883 hv_clock.flags = 0;
1884 if (use_master_clock)
1885 hv_clock.flags |= PVCLOCK_TSC_STABLE_BIT;
1886
1887 if (vcpu->pv_time.active) {
1888 /*
1889 * GUEST_STOPPED is only supported by kvmclock, and KVM's
1890 * historic behavior is to only process the request if kvmclock
1891 * is active/enabled.
1892 */
1893 if (vcpu->pvclock_set_guest_stopped_request) {
1894 hv_clock.flags |= PVCLOCK_GUEST_STOPPED;
1895 vcpu->pvclock_set_guest_stopped_request = false;
1896 }
1897 kvm_setup_guest_pvclock(&hv_clock, v, &vcpu->pv_time, 0);
1898
1899 hv_clock.flags &= ~PVCLOCK_GUEST_STOPPED;
1900 }
1901
1902 kvm_hv_setup_tsc_page(v->kvm, &hv_clock);
1903
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2026-07-30 5:11 UTC | newest]
Thread overview: (only message) (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-07-30 5:10 [sean-jc:x86/host_kvmclock_mess 14/15] arch/x86/kvm/x86.c:1875:26: warning: variable 'master_ns' is uninitialized when used here kernel test robot
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.