Sent from my iPhone
> On Aug 7, 2021, at 12:51 AM, Michael Kelley <mikelley@xxxxxxxxxxxxx> wrote:
>
> From: תומר אבוטבול <tomer432100@xxxxxxxxx> Sent: Friday, August 6, 2021 11:03 AM
>
>> Attaching the patches Michael asked for debugging
>> 1) Print the cpumask when < num_possible_cpus():
>> diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
>> index e666f7eaf32d..620f656d6195 100644
>> --- a/arch/x86/hyperv/mmu.c
>> +++ b/arch/x86/hyperv/mmu.c
>> @@ -60,6 +60,7 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,
>> struct hv_tlb_flush *flush;
>> u64 status = U64_MAX;
>> unsigned long flags;
>> + unsigned int cpu_last;
>>
>> trace_hyperv_mmu_flush_tlb_others(cpus, info);
>>
>> @@ -68,6 +69,11 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,
>>
>> local_irq_save(flags);
>>
>> + cpu_last = cpumask_last(cpus);
>> + if (cpu_last > num_possible_cpus()) {
>
> I think this should be ">=" since cpus are numbered starting at zero.
> In your VM with 64 CPUs, having CPU #64 in the list would be error.
>
>> + pr_emerg("ERROR_HYPERV: cpu_last=%*pbl", cpumask_pr_args(cpus));
>> + }
>> +
>> /*
>> * Only check the mask _after_ interrupt has been disabled to avoid the
>> * mask changing under our feet.
>>
>> 2) disable the Hyper-V specific flush routines:
>> diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
>> index e666f7eaf32d..8e77cc84775a 100644
>> --- a/arch/x86/hyperv/mmu.c
>> +++ b/arch/x86/hyperv/mmu.c
>> @@ -235,6 +235,7 @@ static u64 hyperv_flush_tlb_others_ex(const struct cpumask *cpus,
>>
>> void hyperv_setup_mmu_ops(void)
>> {
>> + return;
>> if (!(ms_hyperv.hints & HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED))
>> return;
>
> Otherwise, this code looks good to me and matches what I had in mind.
>
> Note that the function native_flush_tlb_others() is used when the Hyper-V specific
> flush function is disabled per patch #2 above, or when hv_cpu_to_vp_index() returns
> VP_INVALID. In a quick glance through the code, it appears that native_flush_tlb_others()
> will work even if there's a non-existent CPU in the cpumask that is passed as an argument.
> So perhaps an immediate workaround is Patch #2 above.
The current code of hv_cpu_to_vp_index (where I generated the warning ) is returning VP_INVALID in this case (see previous mail) and look like it is not completely workaround the issue.
the cpu is hanging even not panic Will continue watching .
>
>
> Perhaps hyperv_flush_tlb_others() should be made equally tolerant of a non-existent
> CPU being in the list. But if you are willing, I'm still interested in the results of an
> experiment with just Patch #1. I'm curious about what the CPU list looks like when
> it has a non-existent CPU. Is it complete garbage, or is there just one non-existent
> CPU?
>
We will do my be not next week since vacation but the week after
> The other curiosity is that I haven't seen this Linux panic reported by other users,
> and I think it would have come to our attention if it were happening with any frequency.
> You see the problem fairly regularly. So I'm wondering what the difference is.
>
> Michael
