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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id w7sm3521262ejb.3.2020.08.06.04.39.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2020 04:39:10 -0700 (PDT) From: Vitaly Kuznetsov To: "Michael S. Tsirkin" Cc: kvm@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Peter Xu , Julia Suvorova , Andy Lutomirski , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory In-Reply-To: <20200806055008-mutt-send-email-mst@kernel.org> References: <20200728143741.2718593-1-vkuznets@redhat.com> <20200805201851-mutt-send-email-mst@kernel.org> <873650p1vo.fsf@vitty.brq.redhat.com> <20200806055008-mutt-send-email-mst@kernel.org> Date: Thu, 06 Aug 2020 13:39:09 +0200 Message-ID: <87wo2cngv6.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Michael S. Tsirkin" writes: > About the feature bit, I am not sure why it's really needed. A single > mmio access is cheaper than two io accesses anyway, right? So it makes > sense for a kvm guest whether host has this feature or not. > We need to be careful and limit to a specific QEMU implementation > to avoid tripping up bugs, but it seems more appropriate to > check it using pci host IDs. Right, it's just that "running on KVM" is too coarse grained, we just need a way to somehow distinguish between "known/good" and "unknown/buggy" configurations. -- Vitaly