Date: Thu, 22 Nov 2018 12:04:16 -0800 From: Matthew Wilcox <willy@...radead.org> To: Igor Stoppa <igor.stoppa@...il.com> Cc: Andy Lutomirski <luto@...capital.net>, Andy Lutomirski <luto@...nel.org>, Igor Stoppa <igor.stoppa@...wei.com>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, Peter Zijlstra <peterz@...radead.org>, Mimi Zohar <zohar@...ux.vnet.ibm.com>, Dave Chinner <david@...morbit.com>, James Morris <jmorris@...ei.org>, Michal Hocko <mhocko@...nel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-integrity <linux-integrity@...r.kernel.org>, LSM List <linux-security-module@...r.kernel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Jonathan Corbet <corbet@....net>, Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Mike Rapoport <rppt@...ux.vnet.ibm.com>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 10/17] prmem: documentation On Thu, Nov 22, 2018 at 09:27:02PM +0200, Igor Stoppa wrote: > I have studied the code involved with Nadav's patchset. > I am perplexed about these sentences you wrote. > > More to the point (to the best of my understanding): > > poking_init() > ------------- > 1. it gets one random poking address and ensures to have at least 2 > consecutive PTEs from the same PMD > 2. it then proceeds to map/unmap an address from the first of the 2 > consecutive PTEs, so that, later on, there will be no need to > allocate pages, which might fail, if poking from atomic context. > 3. at this point, the page tables are populated, for the address that > was obtained at point 1, and this is ok, because the address is fixed > > write_rare > ---------- > 4. it can happen on any available core / thread at any time, therefore > each of them needs a different address No? Each CPU has its own CR3 (eg each CPU might be running a different user task). If you have _one_ address for each allocation, it may or may not be mapped on other CPUs at the same time -- you simply don't care. The writable address can even be a simple formula to calculate from the read-only address, you don't have to allocate an address in the writable mapping space.
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