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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: kvm <kvm@vger.kernel.org>,
        "the arch\/x86 maintainers" <x86@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Roman Kagan <rkagan@virtuozzo.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "Michael Kelley \(EOSG\)" <Michael.H.Kelley@microsoft.com>,
        Mohammed Gamal <mmorsy@redhat.com>, Cathy Avery <cavery@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 0/8] KVM: x86: hyperv: PV TLB flush for Windows guests
References: <20180516152131.30689-1-vkuznets@redhat.com>
        <CANRm+Czbc61d+bHw1oTwUT3-MBNCU42NWD8=+GyrXATDyDzYEQ@mail.gmail.com>
        <87bmddgrex.fsf@vitty.brq.redhat.com>
Date: Fri, 18 May 2018 13:19:37 +0200
In-Reply-To: <87bmddgrex.fsf@vitty.brq.redhat.com> (Vitaly Kuznetsov's message
        of "Fri, 18 May 2018 13:00:06 +0200")
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Vitaly Kuznetsov <vkuznets@redhat.com> writes:

> Wanpeng Li <kernellwp@gmail.com> writes:
>
>> Hi Vitaly,
>> 2018-05-16 23:21 GMT+08:00 Vitaly Kuznetsov <vkuznets@redhat.com>:
>>> Changes since v3 [Radim Krcmar]:
>>> - PATCH2 fixing 'HV_GENERIC_SET_SPARCE_4K' typo added.
>>> - PATCH5 introducing kvm_make_vcpus_request_mask() API added.
>>> - Fix undefined behavior for hv->vp_index >= 64.
>>> - Merge kvm_hv_flush_tlb() and kvm_hv_flush_tlb_ex()
>>> - For -ex case preload all banks with a single kvm_read_guest().
>>>
>>> Description:
>>>
>>> This is both a new feature and a bugfix.
>>>
>>> Bugfix description:
>>>
>>> It was found that Windows 2016 guests on KVM crash when they have > 64
>>> vCPUs, non-flat topology (>1 core/thread per socket; in case it has >64
>>> sockets Windows just ignores vCPUs above 64) and Hyper-V enlightenments
>>
>> We try the below command line, the Windows 2016 guest successfully to
>> login and there are 80 vCPUs can be observed in the guest w/o the
>> patchset, why you mentioned the crash and ignore?
>>
>> /usr/local/bin/qemu-system-x86_64 -machine  pc-i440fx-rhel7.3.0  -m
>> 8192 -smp 80,sockets=2,cores=40,threads=1  -device
>> ide-drive,bus=ide.0,drive=test -drive
>> id=test,if=none,file=/instanceimage/359b18ab-05bb-460d-9b53-89505bca68ed/359b18ab-05bb-460d-9b53-89505bca68ed_vda_1.qcow2
>>  -net nic,model=virtio -net user -monitor stdio -usb -usbdevice tablet
>> --enable-kvm --cpu host -vnc 0.0.0.0:2
>
> Crash happens when you manifest yourself as Hyper-V, you can do this by
> adding any 'hv-*' feature (e.g. try '-cpu host,hv_vpindex'). 

Oh, and the 'ignore' happens when you pass more than 64 sockets
(somthing like "-smp 128,sockets=128,cores=1,threads=1") -- and this
happens regardless of Hyper-V enlightenments. But I guess it's just
because Windows doesn't support more than 64 sockets.

-- 
  Vitaly