From 0522604b09b8cff54ba2450a7478da2a4d084817 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Fernando=20Luis=20V=C3=A1zquez=20Cao?= Date: Fri, 6 Dec 2013 17:33:01 +0900 Subject: target-i386: clear guest TSC on reset MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Cc: Marcelo Tosatti Signed-off-by: Fernando Luis Vazquez Cao Signed-off-by: Paolo Bonzini Signed-off-by: Fernando Luis Vázquez Cao --- target-i386/kvm.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'target-i386/kvm.c') diff --git a/target-i386/kvm.c b/target-i386/kvm.c index 312a46bcb9..285e1a3dc8 100644 --- a/target-i386/kvm.c +++ b/target-i386/kvm.c @@ -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); -- cgit v1.2.1