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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id bk12-20020a0560001d8c00b0022762b0e2a2sm10240844wrb.6.2022.09.13.02.40.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Sep 2022 02:40:31 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: Gerd Hoffmann , kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H. Peter Anvin" , "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH] kvm/x86: reserve bit KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID In-Reply-To: References: <20220908114146.473630-1-kraxel@redhat.com> <20220909050224.rzlt4x7tjrespw3k@sirius.home.kraxel.org> <87tu5grkcm.fsf@redhat.com> Date: Tue, 13 Sep 2022 11:40:30 +0200 Message-ID: <87a673r4s1.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > On Fri, Sep 09, 2022, Vitaly Kuznetsov wrote: ... >> While this certainly looks like an overkill here, we could probably add >> new, VMM-spefific CPUID leaves to KVM, e.g. >> >> 0x4000000A: VMM signature >> 0x4000000B: VMM features >> 0x4000000C: VMM quirks >> ... >> >> this way VMMs (like QEMU) could identify themselves and suggest VMM >> specific things to guests without KVM's involvement. Just if 'fw_cfg' is >> not enough) > > I don't think KVM needs to get involved in that either. The de facto hypervisor > CPUID standard already allows for multiple hypervisors/VMMs to announce themselves > to the guest, e.g. QEMU could add itself as another VMM using 0x40000100 (shifted > as necessary to accomodate KVM+Hyper-V). True, VMM can just use another hypervisor space (+0x100) but we can view it from a slightly different angle: KVM itself is insufficient to run VMs, there's always a VMM in the background, we may want to provide a "standard" for its information meaning guests won't need to search for VMMs signature[s] but can directly refer to "standardized" leaves. (All this is a purely theoretical discussion at this point, we need a good reason to introduce this first). -- Vitaly