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[173.76.246.42]) by smtp.gmail.com with ESMTPSA id q57sm3931129qtj.79.2019.03.07.18.21.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 07 Mar 2019 18:21:05 -0800 (PST) Date: Thu, 7 Mar 2019 21:21:03 -0500 From: "Michael S. Tsirkin" To: Jerome Glisse Cc: Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address Message-ID: <20190307211506-mutt-send-email-mst@kernel.org> References: <1551856692-3384-1-git-send-email-jasowang@redhat.com> <1551856692-3384-6-git-send-email-jasowang@redhat.com> <20190307103503-mutt-send-email-mst@kernel.org> <20190307124700-mutt-send-email-mst@kernel.org> <20190307191720.GF3835@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190307191720.GF3835@redhat.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 07, 2019 at 02:17:20PM -0500, Jerome Glisse wrote: > > It's because of all these issues that I preferred just accessing > > userspace memory and handling faults. Unfortunately there does not > > appear to exist an API that whitelists a specific driver along the lines > > of "I checked this code for speculative info leaks, don't add barriers > > on data path please". > > Maybe it would be better to explore adding such helper then remapping > page into kernel address space ? I explored it a bit (see e.g. thread around: "__get_user slower than get_user") and I can tell you it's not trivial given the issue is around security. So in practice it does not seem fair to keep a significant optimization out of kernel because *maybe* we can do it differently even better :) -- MST