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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id c15sm1343755edm.47.2020.07.29.02.22.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jul 2020 02:22:46 -0700 (PDT) From: Vitaly Kuznetsov To: Alexander Graf , Jim Mattson Cc: Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Wanpeng Li , Joerg Roedel , kvm list , linux-doc@vger.kernel.org, LKML , Aaron Lewis Subject: Re: [PATCH] KVM: x86: Deflect unknown MSR accesses to user space In-Reply-To: <173948e8-4c7a-6dc4-de17-99151bc56d91@amazon.com> References: <20200728004446.932-1-graf@amazon.com> <87d04gm4ws.fsf@vitty.brq.redhat.com> <87y2n2log7.fsf@vitty.brq.redhat.com> <173948e8-4c7a-6dc4-de17-99151bc56d91@amazon.com> Date: Wed, 29 Jul 2020 11:22:45 +0200 Message-ID: <87pn8ellp6.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Alexander Graf writes: > On 29.07.20 10:23, Vitaly Kuznetsov wrote: >> >> >> >> Jim Mattson writes: >> >>> On Tue, Jul 28, 2020 at 5:41 AM Alexander Graf wrote: >>>> >> >> ... >> >>>> While it does feel a bit overengineered, it would solve the problem that >>>> we're turning in-KVM handled MSRs into an ABI. >>> >>> It seems unlikely that userspace is going to know what to do with a >>> large number of MSRs. I suspect that a small enumerated list will >>> suffice. >> >> The list can also be 'wildcarded', i.e. >> { >> u32 index; >> u32 mask; >> ... >> } >> >> to make it really short. > > I like the idea of wildcards, but I can't quite wrap my head around how > we would implement ignore_msrs in user space with them? > For that I think we can still deflect all unknown MSR accesses to userspace (when the CAP is enabled of course ) but MSRs which are on the list will *have to be deflected*, i.e. KVM can't handle them internally without consulting with userspace. We can make it tunable through a parameter for CAP enablement if needed. -- Vitaly