On Thu, Mar 24, 2022 at 06:31:36PM +0100, Paolo Bonzini wrote: > Some versions of Windows hang on reboot if their TSC value is greater > than 2^54. The calibration of the Hyper-V reference time overflows > and fails; as a result the processors' clock sources are out of sync. > > The issue is that the TSC _should_ be reset to 0 on CPU reset and > QEMU tries to do that. However, KVM special cases writing 0 to the > TSC and thinks that QEMU is trying to hot-plug a CPU, which is > correct the first time through but not later. Thwart this valiant > effort and reset the TSC to 1 instead, but only if the CPU has been > run once. > > For this to work, env->tsc has to be moved to the part of CPUArchState > that is not zeroed at the beginning of x86_cpu_reset. > > Reported-by: Vadim Rozenfeld <vroze...@redhat.com> > Supersedes: <20220324082346.72180-1-pbonz...@redhat.com> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
Paolo, Won't this disable the logic to sync TSCs, making it possible for TSC of SMP guests to go out of sync? (And remember the logic to sync TSCs from within a guest is fragile, in case of VCPU overload for example). > --- > target/i386/cpu.c | 13 +++++++++++++ > target/i386/cpu.h | 2 +- > 2 files changed, 14 insertions(+), 1 deletion(-) > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index ec3b50bf6e..cb6b5467d0 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -5931,6 +5931,19 @@ static void x86_cpu_reset(DeviceState *dev) > env->xstate_bv = 0; > > env->pat = 0x0007040600070406ULL; > + > + if (kvm_enabled()) { > + /* > + * KVM handles TSC = 0 specially and thinks we are hot-plugging > + * a new CPU, use 1 instead to force a reset. > + */ > + if (env->tsc != 0) { > + env->tsc = 1; > + } > + } else { > + env->tsc = 0; > + } > + > env->msr_ia32_misc_enable = MSR_IA32_MISC_ENABLE_DEFAULT; > if (env->features[FEAT_1_ECX] & CPUID_EXT_MONITOR) { > env->msr_ia32_misc_enable |= MSR_IA32_MISC_ENABLE_MWAIT; > diff --git a/target/i386/cpu.h b/target/i386/cpu.h > index e31e6bd8b8..982c532353 100644 > --- a/target/i386/cpu.h > +++ b/target/i386/cpu.h > @@ -1554,7 +1554,6 @@ typedef struct CPUArchState { > target_ulong kernelgsbase; > #endif > > - uint64_t tsc; > uint64_t tsc_adjust; > uint64_t tsc_deadline; > uint64_t tsc_aux; > @@ -1708,6 +1707,7 @@ typedef struct CPUArchState { > int64_t tsc_khz; > int64_t user_tsc_khz; /* for sanity check only */ > uint64_t apic_bus_freq; > + uint64_t tsc; > #if defined(CONFIG_KVM) || defined(CONFIG_HVF) > void *xsave_buf; > uint32_t xsave_buf_len; > -- > 2.35.1 > > >