From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC751C433FE for ; Thu, 18 Nov 2021 15:24:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF9C46126A for ; Thu, 18 Nov 2021 15:24:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232079AbhKRP1i (ORCPT ); Thu, 18 Nov 2021 10:27:38 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:47164 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230205AbhKRP1b (ORCPT ); Thu, 18 Nov 2021 10:27:31 -0500 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id B07C6212C4; Thu, 18 Nov 2021 15:24:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637249069; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zRV7uWQt5wOO82GENZMQXL2ufpBPou91oq1HzKO2zYU=; b=NcASZNZR1e/nAIkAPJS9d2RbsXwbTfERAXm1kQsPh04XyOd6ft4KD29Qqriur+LdNQI4ze 6F8gJOEUJ9H2m6DfzdmusItVkP3bl6orMfdfxE9YmTEgkJ4F8R3oMPjVfQ4FSsPHQnC+IL PZNLQInJxh8N03HFRIL8UyKGqFB6+Ps= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 3BDF213D43; Thu, 18 Nov 2021 15:24:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id GfRqDS1wlmFwHgAAMHmgww (envelope-from ); Thu, 18 Nov 2021 15:24:29 +0000 To: Sean Christopherson Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" References: <20211116141054.17800-1-jgross@suse.com> <20211116141054.17800-4-jgross@suse.com> From: Juergen Gross Subject: Re: [PATCH v3 3/4] x86/kvm: add max number of vcpus for hyperv emulation Message-ID: Date: Thu, 18 Nov 2021 16:24:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="X6jJQE3N0K8ymlGjTFBbrgWYnUljfCxw0" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --X6jJQE3N0K8ymlGjTFBbrgWYnUljfCxw0 Content-Type: multipart/mixed; boundary="tOiQG9FrlPl3W6AdWehUB6831YZbWNdhn"; protected-headers="v1" From: Juergen Gross To: Sean Christopherson Cc: kvm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Message-ID: Subject: Re: [PATCH v3 3/4] x86/kvm: add max number of vcpus for hyperv emulation References: <20211116141054.17800-1-jgross@suse.com> <20211116141054.17800-4-jgross@suse.com> In-Reply-To: --tOiQG9FrlPl3W6AdWehUB6831YZbWNdhn Content-Type: multipart/mixed; boundary="------------CFC25338D1A051C3E504BEEE" Content-Language: en-US This is a multi-part message in MIME format. --------------CFC25338D1A051C3E504BEEE Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 18.11.21 15:49, Sean Christopherson wrote: > On Thu, Nov 18, 2021, Juergen Gross wrote: >> On 17.11.21 21:50, Sean Christopherson wrote: >>>> @@ -166,7 +166,7 @@ static struct kvm_vcpu *get_vcpu_by_vpidx(struct= kvm *kvm, u32 vpidx) >>>> struct kvm_vcpu *vcpu =3D NULL; >>>> int i; >>>> - if (vpidx >=3D KVM_MAX_VCPUS) >>>> + if (vpidx >=3D min(KVM_MAX_VCPUS, KVM_MAX_HYPERV_VCPUS)) >>> >>> IMO, this is conceptually wrong. KVM should refuse to allow Hyper-V = to be enabled >>> if the max number of vCPUs exceeds what can be supported, or should r= efuse to create >> >> TBH, I wasn't sure where to put this test. Is there a guaranteed >> sequence of ioctl()s regarding vcpu creation (or setting the max >> number of vcpus) and the Hyper-V enabling? >=20 > For better or worse (mostly worse), like all other things CPUID, Hyper-= V is a per-vCPU > knob. If KVM can't detect the impossible condition at compile time, kv= m_check_cpuid() > is probably the right place to prevent enabling Hyper-V on an unreachab= le vCPU. With HYPERV_CPUID_IMPLEMENT_LIMITS already returning the supported number of vcpus for the Hyper-V case I'm not sure there is really more needed. The problem I'm seeing is that the only thing I can do is to let kvm_get_hv_cpuid() not adding the Hyper-V cpuid leaves for vcpus > 64. I can't return a failure, because that would probably let vcpu creation fail. And this is something we don't want, as kvm_get_hv_cpuid() is called even in the case the guest doesn't plan to use Hyper-V extensions. >=20 >>> the vCPUs. I agree it makes sense to add a Hyper-V specific limit, s= ince there are >>> Hyper-V structures that have a hard limit, but detection of violation= s should be a >>> BUILD_BUG_ON, not a silent failure at runtime. >>> >> >> A BUILD_BUG_ON won't be possible with KVM_MAX_VCPUS being selecteble v= ia >> boot parameter. >=20 > I was thinking that there would still be a KVM-defined max that would c= ap whatever > comes in from userspace. >=20 See my answers to you your other responses. Juergen --------------CFC25338D1A051C3E504BEEE Content-Type: application/pgp-keys; name="OpenPGP_0xB0DE9DD628BF132F.asc" Content-Transfer-Encoding: quoted-printable Content-Description: OpenPGP public key Content-Disposition: attachment; filename="OpenPGP_0xB0DE9DD628BF132F.asc" -----BEGIN PGP PUBLIC KEY BLOCK----- xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOBy= cWx w3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJvedYm8O= f8Z d621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJNwQpd369y= 9bf IhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvxXP3FAp2pkW0xq= G7/ 377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEBAAHNHEp1ZXJnZW4gR= 3Jv c3MgPGpnQHBmdXBmLm5ldD7CwHkEEwECACMFAlOMcBYCGwMHCwkIBwMCAQYVCAIJCgsEFgIDA= QIe AQIXgAAKCRCw3p3WKL8TL0KdB/93FcIZ3GCNwFU0u3EjNbNjmXBKDY4FUGNQH2lvWAUy+dnyT= hpw dtF/jQ6j9RwE8VP0+NXcYpGJDWlNb9/JmYqLiX2Q3TyevpB0CA3dbBQp0OW0fgCetToGIQrg0= MbD 1C/sEOv8Mr4NAfbauXjZlvTj30H2jO0u+6WGM6nHwbh2l5O8ZiHkH32iaSTfN7Eu5RnNVUJbv= oPH Z8SlM4KWm8rG+lIkGurqqu5gu8q8ZMKdsdGC4bBxdQKDKHEFExLJK/nRPFmAuGlId1E3fe10v= 5QL +qHI3EIPtyfE7i9Hz6rVwi7lWKgh7pe0ZvatAudZ+JNIlBKptb64FaiIOAWDCx1SzR9KdWVyZ= 2Vu IEdyb3NzIDxqZ3Jvc3NAc3VzZS5jb20+wsB5BBMBAgAjBQJTjHCvAhsDBwsJCAcDAgEGFQgCC= QoL BBYCAwECHgECF4AACgkQsN6d1ii/Ey/HmQf/RtI7kv5A2PS4RF7HoZhPVPogNVbC4YA6lW7Dr= Wf0 teC0RR3MzXfy6pJ+7KLgkqMlrAbN/8Dvjoz78X+5vhH/rDLa9BuZQlhFmvcGtCF8eR0T1v0nC= /nu AFVGy+67q2DH8As3KPu0344TBDpAvr2uYM4tSqxK4DURx5INz4ZZ0WNFHcqsfvlGJALDeE0Lh= ITT d9jLzdDad1pQSToCnLl6SBJZjDOX9QQcyUigZFtCXFst4dlsvddrxyqT1f17+2cFSdu7+ynLm= XBK 7abQ3rwJY8SbRO2iRulogc5vr/RLMMlscDAiDkaFQWLoqHHOdfO9rURssHNN8WkMnQfvUewRz= 80h SnVlcmdlbiBHcm9zcyA8amdyb3NzQG5vdmVsbC5jb20+wsB5BBMBAgAjBQJTjHDXAhsDBwsJC= AcD AgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey8PUQf/ehmgCI9jB9hlgexLvgOtf7PJn= FOX gMLdBQgBlVPO3/D9R8LtF9DBAFPNhlrsfIG/SqICoRCqUcJ96Pn3P7UUinFG/I0ECGF4EvTE1= jnD kfJZr6jrbjgyoZHiw/4BNwSTL9rWASyLgqlA8u1mf+c2yUwcGhgkRAd1gOwungxcwzwqgljf0= N51 N5JfVRHRtyfwq/ge+YEkDGcTU6Y0sPOuj4Dyfm8fJzdfHNQsWq3PnczLVELStJNdapwPOoE+l= otu fe3AM2vAEYJ9rTz3Cki4JFUsgLkHFqGZarrPGi1eyQcXeluldO3m91NK/1xMI3/+8jbO0tsn1= tqS EUGIJi7ox80eSnVlcmdlbiBHcm9zcyA8amdyb3NzQHN1c2UuZGU+wsB5BBMBAgAjBQJTjHDrA= hsD BwsJCAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey+LhQf9GL45eU5vOowA2u5N3= g3O ZUEBmDHVVbqMtzwlmNC4k9Kx39r5s2vcFl4tXqW7g9/ViXYuiDXb0RfUpZiIUW89siKrkzmQ5= dM7 wRqzgJpJwK8Bn2MIxAKArekWpiCKvBOB/Cc+3EXE78XdlxLyOi/NrmSGRIov0karw2RzMNOu5= D+j LRZQd1Sv27AR+IP3I8U4aqnhLpwhK7MEy9oCILlgZ1QZe49kpcumcZKORmzBTNh30FVKK1Evm= V2x AKDoaEOgQB4iFQLhJCdP1I5aSgM5IVFdn7v5YgEYuJYx37IoN1EblHI//x/e2AaIHpzK5h88N= Eaw QsaNRpNSrcfbFmAg987ATQRTjHAWAQgAyzH6AOODMBjgfWE9VeCgsrwH3exNAU32gLq2xvjpW= nHI s98ndPUDpnoxWQugJ6MpMncr0xSwFmHEgnSEjK/PAjppgmyc57BwKII3sV4on+gDVFJR6Y8ZR= wgn BC5mVM6JjQ5xDk8WRXljExRfUX9pNhdE5eBOZJrDRoLUmmjDtKzWaDhIg/+1Hzz93X4fCQkNV= bVF LELU9bMaLPBG/x5q4iYZ2k2ex6d47YE1ZFdMm6YBYMOljGkZKwYde5ldM9mo45mmwe0icXKLk= pEd IXKTZeKDO+Hdv1aqFuAcccTg9RXDQjmwhC3yEmrmcfl0+rPghO0Iv3OOImwTEe4co3c1mwARA= QAB wsBfBBgBAgAJBQJTjHAWAhsMAAoJELDendYovxMvQ/gH/1ha96vm4P/L+bQpJwrZ/dneZcmEw= Tbe 8YFsw2V/Buv6Z4Mysln3nQK5ZadD534CF7TDVft7fC4tU4PONxF5D+/tvgkPfDAfF77zy2AH1= vJz Q1fOU8lYFpZXTXIHb+559UqvIB8AdgR3SAJGHHt4RKA0F7f5ipYBBrC6cyXJyyoprT10EMvU8= VGi wXvTyJz3fjoYsdFzpWPlJEBRMedCot60g5dmbdrZ5DWClAr0yau47zpWj3enf1tLWaqcsuylW= svi uGjKGw7KHQd3bxALOknAp4dN3QwBYCKuZ7AddY9yjynVaD5X7nF9nO5BjR/i1DG86lem3iBDX= zXs ZDn8R38=3D =3D2wuH -----END PGP PUBLIC KEY BLOCK----- --------------CFC25338D1A051C3E504BEEE-- --tOiQG9FrlPl3W6AdWehUB6831YZbWNdhn-- --X6jJQE3N0K8ymlGjTFBbrgWYnUljfCxw0 Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature" -----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAmGWcCwFAwAAAAAACgkQsN6d1ii/Ey/r iQf/bolwpowY42dhidl7jgDoUN3L3lBwGIzssu1WU62NiW0BrC+bCEIx1iQxRlnzbSTzbPad8qsO 3loR2LLouWRaklV2BG8lolbXm4R1GDvq5zP/2DaDY9PBV2XkE0tJ2pPvOvOiki+BMejjDhAN9DEZ JaiSlkmGTTjK0aaNAm6LSQHfXEYcfLHv6IDytXPq4zCVGFtpNNlFWwXi1h8B6W2XhHuUa84ynZTR R+Lil6D9RKWQJve6fJ3zrW5dtvffPDllpnH21ER5Y5sbOZL1P5XB/fk5dX+AK6y+ayhDylLFngOB kut6ozNOEl0wAXQm3/QBixhFyNrG8OfLTkOPE4QgxA== =E+2E -----END PGP SIGNATURE----- --X6jJQE3N0K8ymlGjTFBbrgWYnUljfCxw0--