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Following the rework, cpuid_level has a > placeholder 1 until it is caluclated propely. > > setup_apic_nmi_watchdog() happens to be called on the BSP after SMP bringup, > meaning that the first call is on CPU1. It is also positioned in the window > where cpu_data[] is garbage. > > As a result, setup_p6_watchdog()'s one-time calculation of the performance > counter width falls back into Pentium compatibility mode assuming 32bit > counters. This causes a watchdog NMI which is delayed a little (e.g. from an > SMI), to appear as if it hadn't overflowed, and therefore be (mis)classifed as > not a watchdog NMI. On systems where unknown NMIs are treated as fatal, this > results in a spurious crash. > > Switch setup_p6_watchdog() to use boot_cpu_data.cpuid_level, which is how this > is checked almost everywhere else. > > core2_vpmu_init() used the same pattern to look at leaf 0xa. Despite being > init code and only running on the BSP, {boot,current}_cpu_data are different > objects, so switch it over to checking boot_cpu_data.cpuid_level too. > > Fixes: 7126b7f806d5 ("x86/CPU: re-work populating of cpu_data[]") > Signed-off-by: Andrew Cooper > --- > CC: Jan Beulich > CC: Roger Pau Monné > CC: Teddy Astie > > Found on a system where: > > [root@box ~]# time xen-ucode ./blob > > real 0m9.166s > user 0m0.001s > sys 0m9.165s > > is changing several expectations, and spurious crashes from mis-classified > watchdog NMIs is just one part of the problem. > > I hate this fix, but it's the only thing which I consider remotely safe to > backport. Recent attempts to alter CPUID ordering have 0 success at being > bug-free. > > I have not investigated what else was broken by the cpu_data[] change, owing > to a lack of time on my part. I would be amazed if this is the only thing. > --- > xen/arch/x86/cpu/vpmu_intel.c | 2 +- > xen/arch/x86/nmi.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/xen/arch/x86/cpu/vpmu_intel.c b/xen/arch/x86/cpu/vpmu_intel.c > index ed9f62b9366d..af6cb0a85cdd 100644 > --- a/xen/arch/x86/cpu/vpmu_intel.c > +++ b/xen/arch/x86/cpu/vpmu_intel.c > @@ -896,7 +896,7 @@ const struct arch_vpmu_ops *__init core2_vpmu_init(void) > unsigned int version = 0; > unsigned int i; > > - if ( current_cpu_data.cpuid_level >= 0xa ) > + if ( bsp_cpu_data.cpuid_level >= 0xa ) > version = MASK_EXTR(cpuid_eax(0xa), PMU_VERSION_MASK); Hmm, this is a stale copy of the patch.  Fixed locally. ~Andrew > > switch ( version ) > diff --git a/xen/arch/x86/nmi.c b/xen/arch/x86/nmi.c > index 91f95fe6d080..ec85516609b0 100644 > --- a/xen/arch/x86/nmi.c > +++ b/xen/arch/x86/nmi.c > @@ -321,7 +321,7 @@ static void setup_p6_watchdog(unsigned counter) > { > unsigned int evntsel; > > - if ( !nmi_p6_event_width && current_cpu_data.cpuid_level >= 0xa ) > + if ( !nmi_p6_event_width && boot_cpu_data.cpuid_level >= 0xa ) > nmi_p6_event_width = MASK_EXTR(cpuid_eax(0xa), P6_EVENT_WIDTH_MASK); > if ( !nmi_p6_event_width ) > nmi_p6_event_width = P6_EVENT_WIDTH_MIN;