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Thu, 14 Oct 2021 23:12:48 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzf+rzfxV14NiwTVJQgWw72UWHpbHWXweeDvuvWXiiN5B+2IT/crec+mJl6l1rQQFzSMkv/lQ== X-Received: by 2002:a05:6a00:b8f:b0:44c:6220:3396 with SMTP id g15-20020a056a000b8f00b0044c62203396mr9842943pfj.58.1634278367983; Thu, 14 Oct 2021 23:12:47 -0700 (PDT) Received: from t490s ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id r130sm4030255pfc.89.2021.10.14.23.12.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 Oct 2021 23:12:47 -0700 (PDT) Date: Fri, 15 Oct 2021 14:12:42 +0800 From: Peter Xu To: lma Subject: Re: [PATCH 0/3] Postcopy migration: Add userfaultfd- user-mode-only capability Message-ID: References: <20211014091551.15201-1-lma@suse.com> <7c0161fab24b06fa249061780a7f30d4@suse.de> MIME-Version: 1.0 In-Reply-To: <7c0161fab24b06fa249061780a7f30d4@suse.de> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.049, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: qemu-devel@nongnu.org, dgilbert@redhat.com, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Oct 15, 2021 at 01:38:06PM +0800, lma wrote: > 在 2021-10-15 07:43，Peter Xu 写道： > > On Thu, Oct 14, 2021 at 05:15:48PM +0800, Lin Ma wrote: > > > Since kernel v5.11, Unprivileged user (without SYS_CAP_PTRACE > > > capability) > > > must pass UFFD_USER_MODE_ONLY to userfaultd in case > > > unprivileged_userfaultfd > > > sysctl knob is 0. > > > Please refer to https://lwn.net/Articles/819834/ and the kernel > > > commits: > > > 37cd0575 userfaultfd: add UFFD_USER_MODE_ONLY > > > d0d4730a userfaultfd: add user-mode only option to > > > unprivileged_userfaultfd sysctl knob > > > > > > This patch set adds a migration capability to pass UFFD_USER_MODE_ONLY > > > for postcopy migration. > > > > Then it's at least no KVM, no vhost, am I right? Could I ask is there a > > real > > user behind this? Thanks, > > Well, The "user-mode-only" has nothing to do with qemu's user-mode > emulation. I didn't follow why you thought my question was about "user-mode emulation".. To ask in another way: after this new cap set, qemu will get a SIGBUS and VM will crash during postcopy migrating as long as either KVM or vhost-kernel faulted on any of the missing pages, am I right? Thanks, -- Peter Xu