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[150.31.62.179]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2cf8f350560sm46337545ad.68.2026.07.23.23.53.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2026 23:53:59 -0700 (PDT) Date: Fri, 24 Jul 2026 15:53:55 +0900 Message-ID: From: Hajime Tazaki To: johannes@sipsolutions.net Cc: linux-um@lists.infradead.org, liam@infradead.org, ljs@kernel.org, ricarkol@google.com Subject: Re: [PATCH v2 10/10] Documentation: um: document nommu UML In-Reply-To: References: <20260723093633.140989-12-johannes@sipsolutions.net> <20260723113633.19c6669dc151.Ibd7a532eef856a1ea39699a263dfa8a9ded9dc20@changeid> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/26.3 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260723_235401_390655_589C54A9 X-CRM114-Status: GOOD ( 27.54 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On Fri, 24 Jul 2026 15:49:08 +0900, Johannes Berg wrote: > > On Fri, 2026-07-24 at 15:20 +0900, Hajime Tazaki wrote: > > > UML models this with > > > +a **userspace runner** - an ordinary uml-userspace stub host process, started > > > +exactly like an MMU userspace process, but with the whole of "physical" memory > > > +(the physmem file) mapped into it at the kernel's addresses: > > > + > > > +- The runner ``exec()``'s the stub just like the MMU case. The only extra step > > > + is that, once it is up, the kernel maps the entire physmem file into it in one > > > + go, at the same addresses the kernel uses. > > > +- Because NOMMU never remaps, that single mapping is all a runner ever needs: > > > > I was actually not sure what you mean here: "NOMMU never remaps". > > could you care to elaborate ? > > the subsequent parts are clear to me. > > Yeah maybe, that's a bit cryptic. I mean, we have an MMU-less base > kernel, so there's never any request to remap for anything, so > > > > + there is no per-mm host process, no TLB sync and no ``mmap()`` of individual > > > + page-table entries into a child. Userspace code and data - placed in memory > > > + by the loader - are directly executable and accessible. > > the original mapping that we make into that process is left alone > forever. The map machinery in the stub is used only exactly once. make sense to me, thanks. > > For the alpine packages, I'll contact the distribution once this UML > > is upstreamed. And update this part with more proper information > > rather than my personal repository. > > Sure. It seemed far simpler to point to it than to try to have > instructions on how to build it (I didn't even try), and I'm assuming > you don't plan to remove it :) I will keep this image location but using version number will easily outdate while it's useful to present a snapshot for users. -- Hajime