[PULL 6/7] target/i386: properly reset TSC on reset

[Paolo Bonzini]

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 <vrozenfe@redhat.com>
Supersedes: <20220324082346.72180-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 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