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Tue, 26 Nov 2019 14:07:38 +0000 (UTC) Received: from [10.36.117.163] (ovpn-117-163.ams2.redhat.com [10.36.117.163]) by smtp.corp.redhat.com (Postfix) with ESMTP id 816BD393B; Tue, 26 Nov 2019 14:07:32 +0000 (UTC) Subject: Re: [PATCH v2 2/2] s390x/cpumodel: Introduce dynamic feature groups To: Christian Borntraeger References: From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAj4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI 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+uQINBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/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+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABiQIl 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: Date: Tue, 26 Nov 2019 15:07:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: pkTlcgn1NY2F6MYwsS26kw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , Janosch Frank , Cornelia Huck , Richard Henderson , qemu-devel@nongnu.org, Markus Armbruster , Halil Pasic , qemu-s390x@nongnu.org, Jiri Denemark , Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 26.11.19 13:59, Christian Borntraeger wrote: > re-adding ccs from the cover-letter >=20 >>>> On 25.11.19 18:20, David Hildenbrand wrote: >>>> >>>> As soon as dynamic feature groups are used, the CPU model becomes >>>> migration-unsafe. Upper layers can expand these models to migration-sa= fe >>>> and static variants, allowing them to be migrated. >>> >>> I really dislike that. I am trying to get rid of the unsafe variants (e= .g. now >>> defaulting to host-model instead of host-passthrough). I do not want to= give >>> users new ways of hurting themselves. >>> >> >> Please note that this is just on the bare command line. Libvirt and frie= nds will expand the model and have proper migration in place. What exactly = is your concern in that regard? >=20 > What is then the value? libvirt can also use host-model or baselining if= necessary. > And for the command line this will just add more opportunity to shot your= self in the > foot, no? I don't think so. It's in no way more dangerous than "-cpu host" or "-cpu max". And it is in no way more dangerous than the discussed CPU versions, where even a "-cpu z13" would no longer be migration-safe. You could - in theory - baseline(z13, host), but it could suddenly fallback to a, say, zEC12 - and that's not what you asked for. And you should not simply mask of deprecated features when baselining. Sure, we could eventually add config knobs for that , but ... ... I really do like the part where you can specify on the command line to have specific CPU definition, but including all available/recommended features (e.g., nested virtualization). >=20 > Let me put it this way, I might have misunderstood what you are trying to= do here, > but if I do not get, then others (e.g. users) will also not get it. I remember you participated in the relevant discussions. That's where we also agreed that versioned CPU models on s390x don't make any sense. But I can refine what's included in this patch description "There is the demand from higher levels in the stack to "have the best CPU model possible on a given accelerator, firmware and HW"" - the best CPU model for a specific *CPU definition*. Say the user has the option to select a model (zEC12, z13, z14), upper layers always want to have a model that includes all backported security features. While the host model can do that, CPU definitions can't. You can't change default models within a QEMU release, or for older releases (e.g., a z13). >=20 > Maybe its just the interface or the name. But I find this very non-intuit= ive I'm open for suggestions. >=20 > e.g. you wrote >=20 > Get the maximum possible feature set (e.g., including deprecated > features) for a CPU definition in the configuration ("everything that > could be enabled"): > -cpu z14,all-features=3Doff,available-features=3Don >=20 > Get all valid features for a CPU definition: > -cpu z14,all-features=3Don >=20 > What is the point of this? It is either the same as the one before, or it= wont > be able to start.=20 valid !=3D available, all !=3D available. Yes, the model won't run unless you are on pretty good HW :) Maybe I should just have dropped the last example, as it seems to confuse people - it's mostly only relevant for introspection via CPU model expansion. I am open for better names. e.g. all-features -> valid-features. --=20 Thanks, David / dhildenb