Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v9 21/22] KVM: s390: CPU model support for AP
 virtualization
To:     Halil Pasic <pasic@linux.ibm.com>,
        Tony Krowiak <akrowiak@linux.ibm.com>,
        Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     freude@de.ibm.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, borntraeger@de.ibm.com,
        cohuck@redhat.com, kwankhede@nvidia.com,
        bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com,
        alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com,
        alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com,
        jjherne@linux.vnet.ibm.com, thuth@redhat.com,
        pasic@linux.vnet.ibm.com, berrange@redhat.com,
        fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com,
        frankja@linux.ibm.com
References: <1534196899-16987-1-git-send-email-akrowiak@linux.vnet.ibm.com>
 <1534196899-16987-22-git-send-email-akrowiak@linux.vnet.ibm.com>
 <2c2c4859-ed3e-a492-dd59-78529c7768b2@redhat.com>
 <95e6ee74-69aa-9805-3233-b9ec81fce516@redhat.com>
 <7e7a35f5-d1eb-7719-c5e8-57d6f19db675@linux.ibm.com>
 <f5ec13ae-75b4-918e-aaf1-ed97944ff16e@redhat.com>
 <fec90446-7f94-da28-d958-427a0446854e@linux.ibm.com>
From:   David Hildenbrand <david@redhat.com>
Openpgp: preference=signencrypt
Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata=
 xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ
 dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL
 QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp
 XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK
 Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9
 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt
 WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc
 UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv
 jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb
 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk
 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI
 BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG
 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj
 xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3
 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob
 s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM
 m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez
 MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK
 z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh
 dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E
 UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq
 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga
 uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid
 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X
 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+
 xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC
 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb
 hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC
 u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS
 gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg
 rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl
 BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl
 KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ
 NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo
 YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5
 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy
 qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl
 C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV
 W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV
 TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx
 +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl
 SE+xAvmumFBY
Organization: Red Hat GmbH
Message-ID: <ef6082b7-da96-3a0b-77a0-f41d113d058a@redhat.com>
Date:   Thu, 23 Aug 2018 12:28:09 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <fec90446-7f94-da28-d958-427a0446854e@linux.ibm.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 23.08.2018 12:00, Halil Pasic wrote:
> 
> 
> On 08/23/2018 09:44 AM, David Hildenbrand wrote:
>> On 22.08.2018 22:16, Tony Krowiak wrote:
>>> On 08/22/2018 07:24 AM, David Hildenbrand wrote:
>>>> On 22.08.2018 13:19, David Hildenbrand wrote:
>>>>> On 13.08.2018 23:48, Tony Krowiak wrote:
>>>>>> From: Tony Krowiak <akrowiak@linux.ibm.com>
>>>>>>
>>>>>> Introduces a new CPU model feature and two CPU model
>>>>>> facilities to support AP virtualization for KVM guests.
>>>>>>
>>>>>> CPU model feature:
>>>>>>
>>>>>> The KVM_S390_VM_CPU_FEAT_AP feature indicates that
>>>>>> AP instructions are available on the guest. This
>>>>>> feature will be enabled by the kernel only if the AP
>>>>>> instructions are installed on the linux host. This feature
>>>>>> must be specifically turned on for the KVM guest from
>>>>>> userspace to use the VFIO AP device driver for guest
>>>>>> access to AP devices.
>>>>>>
>>>>>> CPU model facilities:
>>>>>>
>>>>>> 1. AP Query Configuration Information (QCI) facility is installed.
>>>>>>
>>>>>>      This is indicated by setting facilities bit 12 for
>>>>>>      the guest. The kernel will not enable this facility
>>>>>>      for the guest if it is not set on the host.
>>>>>>
>>>>>>      If this facility is not set for the KVM guest, then only
>>>>>>      APQNs with an APQI less than 16 will be used by a Linux
>>>>>>      guest regardless of the matrix configuration for the virtual
>>>>>>      machine. This is a limitation of the Linux AP bus.
>>>>>>
>>>>>> 2. AP Facilities Test facility (APFT) is installed.
>>>>>>
>>>>>>      This is indicated by setting facilities bit 15 for
>>>>>>      the guest. The kernel will not enable this facility for
>>>>>>      the guest if it is not set on the host.
>>>>>>
>>>>>>      If this facility is not set for the KVM guest, then no
>>>>>>      AP devices will be available to the guest regardless of
>>>>>>      the guest's matrix configuration for the virtual
>>>>>>      machine. This is a limitation of the Linux AP bus.
>>>>>>
>>>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>>>>>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>>>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
>>>>>> Tested-by: Michael Mueller <mimu@linux.ibm.com>
>>>>>> Tested-by: Farhan Ali <alifm@linux.ibm.com>
>>>>>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>>>> ---
>>>>>>    arch/s390/kvm/kvm-s390.c         |    5 +++++
>>>>>>    arch/s390/tools/gen_facilities.c |    2 ++
>>>>>>    2 files changed, 7 insertions(+), 0 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>>>> index 1e8cb67..d5e04d2 100644
>>>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>>>> @@ -367,6 +367,11 @@ static void kvm_s390_cpu_feat_init(void)
>>>>>>    
>>>>>>    	if (MACHINE_HAS_ESOP)
>>>>>>    		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP);
>>>>>> +
>>>>>> +	/* Check if AP instructions installed on host */
>>>>>> +	if (ap_instructions_available())
>>>>>> +		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP);
>>>>>> +
>>>>>>    	/*
>>>>>>    	 * We need SIE support, ESOP (PROT_READ protection for gmap_shadow),
>>>>>>    	 * 64bit SCAO (SCA passthrough) and IDTE (for gmap_shadow unshadowing).
>>>>>> diff --git a/arch/s390/tools/gen_facilities.c b/arch/s390/tools/gen_facilities.c
>>>>>> index 90a8c9e..a52290b 100644
>>>>>> --- a/arch/s390/tools/gen_facilities.c
>>>>>> +++ b/arch/s390/tools/gen_facilities.c
>>>>>> @@ -106,6 +106,8 @@ struct facility_def {
>>>>>>    
>>>>>>    		.name = "FACILITIES_KVM_CPUMODEL",
>>>>>>    		.bits = (int[]){
>>>>>> +			12, /* AP Query Configuration Information */
>>>>>> +			15, /* AP Facilities Test */
>>>>>>    			-1  /* END */
>>>>>>    		}
>>>>>>    	},
>>>>>>
>>>>> I really wonder if we should also export the APXA facility.
>>>>>
>>>>> We can probe and allow that CPU feature. However, we cannot disable it
>>>>> (as of now).
>>>>>
>>>>> We have other CPU features where it is the same case (basically all
>>>>> subfunctions). See kvm_s390_get_processor_subfunc(). We probe them and
>>>>> export them, but support to disable them has never been implemented.
>>>>>
>>>>> On a high level, we could then e.g. deny to start a QEMU guest if APXA
>>>>> is available but has been disabled. (until we know that disabling it
>>>>> actually works - if ever).
>>>>>
>>>>> This helps to catch nasty migration bugs (e.g. APXA suddenly
>>>>> disappearing). Although unlikely, definitely possible.
>>>>>
>>>>>
>>>>> Are there any other AP related facilities that the guest can from now on
>>>>> probe that should also become part of the CPU model?
>>>>>
>>>> To be more precise, shouldn't PQAP(QCI) be handled just like other
>>>> subfunctions? (I remember it should)
>>>
>>> When you suggest PQAP(QCI) be handled like other subfunctions, are you
>>> suggesting that there should be a field in struct kvm_s390_vm_cpu_subfunc
>>> with a bit indicating the QCI subfunction is available? The availability
>>> of the QCI subfunction of the PQAP instruction is determined by facilities
>>> bit 12. Is it not enough to export facilities bit 12?
>>
>> The feature block (128 bit) from PQAP(QCI) should be passed through a
>> subfunction block to QEMU.
>>
> 
> I'm confused, which 128 bit?


Me too :) , I was assuming this block to be 128bit, but the qci block
has 128 bytes....

And looking at arch/s390/include/asm/ap.h, there is a lot of information
contained that is definitely not of interest for CPU models...

I wonder if there is somewhere defined which bits are reserved for
future features/facilities, compared to ap masks and such.

This is really hard to understand/plan without access to documentation.

You (Halil, Tony, Pier, ...) should have a look if what I described
related to PQAP(QCI) containing features that should get part of the CPU
model makes sense or not. For now I was thinking that there is some part
inside of QCI that is strictly reserved for facilities/features that we
can use.

-- 

Thanks,

David / dhildenb