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([2001:b07:6468:f312:cc23:f353:392:d2ee]) by smtp.gmail.com with ESMTPSA id s188sm40667406wmf.40.2019.07.25.08.35.02 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Thu, 25 Jul 2019 08:35:02 -0700 (PDT) To: "Michael S. Tsirkin" References: <20190703095825.GE11844@stefanha-x1.localdomain> <87d0i7tlkl.fsf@redhat.com> <20190719102915.GG18585@stefanha-x1.localdomain> <8736j2p22w.fsf@redhat.com> <904248411098104fcf7db22382172057e50db76c.camel@intel.com> <87tvbdrvin.fsf@redhat.com> <20190725104331-mutt-send-email-mst@kernel.org> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <6d318abf-4afa-a1dc-a4e8-3a2d0a6de297@redhat.com> Date: Thu, 25 Jul 2019 17:35:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190725104331-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.221.66 Subject: Re: [Qemu-devel] [PATCH v3 0/4] Introduce the microvm machine type X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "ehabkost@redhat.com" , Sergio Lopez , "maran.wilson@oracle.com" , "Montes, Julio" , Stefan Hajnoczi , "qemu-devel@nongnu.org" , "kraxel@redhat.com" , "rth@twiddle.net" , "sgarzare@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 25/07/19 16:46, Michael S. Tsirkin wrote: > Actually, I think I have a better idea. > At the moment we just get an exit on these reads and return all-ones. > Yes, in theory there could be a UR bit set in a bunch of > registers but in practice no one cares about these, > and I don't think we implement them. > So how about mapping a single page, read-only, and filling it > with all-ones? Yes, that's nice indeed. :) But it does have some cost, in terms of either number of VMAs or QEMU RSS since the MMCONFIG area is large. What breaks if we return all zeroes? Zero is not a valid vendor ID. Paolo