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target-i386: clear guest TSC on reset 

VCPU TSC is not cleared by a warm reset (*), which leaves some types of Linux
 guests (non-pvops guests and those with the kernel parameter no-kvmclock set)
vulnerable to the overflow in cyc2ns_offset fixed by upstream commit
9993bc635d01a6ee7f6b833b4ee65ce7c06350b1 ("sched/x86: Fix overflow in
cyc2ns_offset").

To put it in a nutshell, if such a Linux guest without the patch above applied
has been up more than 208 days and attempts a warm reset chances are that
the newly booted kernel will panic or hang.

(*) Intel Xeon E5 processors show the same broken behavior due to
    the errata "TSC is Not Affected by Warm Reset" (Intel® Xeon®
    Processor E5 Family Specification Update - August 2013): "The
    TSC (Time Stamp Counter MSR 10H) should be cleared on
    reset. Due to this erratum the TSC is not affected by warm
    reset."

Cc: Will Auld <will.auld@intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Fernando Luis Vázquez Cao <fernando_b1@lab.ntt.co.jp>
This commit is contained in:
Fernando Luis Vázquez Cao 2013-12-06 17:33:01 +09:00 committed by Paolo Bonzini
parent f86746c263
commit 0522604b09
2 changed files with 4 additions and 3 deletions
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3
target-i386/cpu.c
View File

@ -2450,6 +2450,9 @@ static void x86_cpu_reset(CPUState *s)
cpu_breakpoint_remove_all(env, BP_CPU);
cpu_watchpoint_remove_all(env, BP_CPU);
env->tsc_adjust = 0;
env->tsc = 0;
#if !defined(CONFIG_USER_ONLY)
/* We hard-wire the BSP to the first CPU. */
if (s->cpu_index == 0) {

4
target-i386/kvm.c
View File

@ -1150,14 +1150,12 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
kvm_msr_entry_set(&msrs[n++], MSR_LSTAR, env->lstar);
}
#endif
if (level == KVM_PUT_FULL_STATE) {
kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc);
}
/*
* The following MSRs have side effects on the guest or are too heavy
* for normal writeback. Limit them to reset or full state updates.
*/
if (level >= KVM_PUT_RESET_STATE) {
kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc);
kvm_msr_entry_set(&msrs[n++], MSR_KVM_SYSTEM_TIME,
env->system_time_msr);
kvm_msr_entry_set(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);