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Mon, 18 Sep 2023 08:52:41 -0700 (PDT) Date: Mon, 18 Sep 2023 08:52:40 -0700 In-Reply-To: <20230918152946.GJ13795@ziepe.ca> Mime-Version: 1.0 References: <20230916003118.2540661-1-seanjc@google.com> <20230916003118.2540661-7-seanjc@google.com> <20230918152946.GJ13795@ziepe.ca> Message-ID: Subject: Re: [PATCH 06/26] KVM: Drop CONFIG_KVM_VFIO and just look at KVM+VFIO From: Sean Christopherson To: Jason Gunthorpe Content-Type: text/plain; charset="us-ascii" X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: x86@kernel.org, kvm@vger.kernel.org, Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-kernel@vger.kernel.org, Alexander Gordeev , Claudio Imbrenda , Will Deacon , linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, Janosch Frank , Harald Freudenberger , Marc Zyngier , Huacai Chen , Halil Pasic , Andrew Thornton , Ingo Molnar , Christian Borntraeger , Jason Herne , Albert Ou , Vasily Gorbik , Venkatesh Srinivas , Heiko Carstens , Arnaldo Carvalho de Melo , Alex Williamson , Borislav Petkov , And y Lutomirski , Paul Walmsley , kvmarm@lists.linux.dev, Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Tony Krowiak , Anish Ghulati , linux-mips@vger.kernel.org, Oliver Upton , linux-perf-users@vger.kernel.org, Palmer Dabbelt , kvm-riscv@lists.infradead.org, Anup Patel , Paolo Bonzini , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Sep 18, 2023, Jason Gunthorpe wrote: > On Fri, Sep 15, 2023 at 05:30:58PM -0700, Sean Christopherson wrote: > > Drop KVM's KVM_VFIO Kconfig, and instead compile in VFIO support if > > and only if VFIO itself is enabled. Similar to the recent change to have > > VFIO stop looking at HAVE_KVM, compiling in support for talking to VFIO > > just because the architecture supports VFIO is nonsensical. > > > > This fixes a bug where RISC-V doesn't select KVM_VFIO, i.e. would silently > > fail to do connect KVM and VFIO, even though RISC-V supports VFIO. The > > bug is benign as the only driver in all of Linux that actually uses the > > KVM reference provided by VFIO is KVM-GT, which is x86/Intel specific. > > Hmm, I recall that all the S390 drivers need it as well. > > static int vfio_ap_mdev_open_device(struct vfio_device *vdev) > { > struct ap_matrix_mdev *matrix_mdev = > container_of(vdev, struct ap_matrix_mdev, vdev); > > if (!vdev->kvm) > return -EINVAL; > > return vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm); Ah, I missed that the KVM reference was routed through VFIO in that case. > I wonder if we should be making the VFIO drivers that need the kvm to > ask for it? 'select CONFIG_NEED_VFIO_KVM' or something? I wondered the same thing, if only to make it easier to track which drivers actually end up interacting directly with KVM. > Regardless, I fully agree with getting rid of the arch flag. > > Reviewed-by: Jason Gunthorpe > > > --- a/virt/kvm/Makefile.kvm > > +++ b/virt/kvm/Makefile.kvm > > @@ -6,7 +6,9 @@ > > KVM ?= ../../../virt/kvm > > > > kvm-y := $(KVM)/kvm_main.o $(KVM)/eventfd.o $(KVM)/binary_stats.o > > -kvm-$(CONFIG_KVM_VFIO) += $(KVM)/vfio.o > > +ifdef CONFIG_VFIO > > +kvm-y += $(KVM)/vfio.o > > +endif > > I wonder if kvm-m magically works in kbuild so you don't need the ifdef? Yeah, that should work, no idea why I added the ifdef.