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[46.139.12.213]) by smtp.gmail.com with ESMTPSA id b12sm10623148wrx.11.2018.09.09.23.18.41 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 09 Sep 2018 23:18:41 -0700 (PDT) Date: Mon, 10 Sep 2018 08:18:39 +0200 From: Ingo Molnar To: Baoquan He Cc: tglx@linutronix.de, hpa@zytor.com, thgarnie@google.com, kirill.shutemov@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH v2 1/3] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size Message-ID: <20180910061839.GA90334@gmail.com> References: <20180909124946.17988-1-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180909124946.17988-1-bhe@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Baoquan He wrote: > In memory KASLR, __PHYSICAL_MASK_SHIFT is taken to calculate the > initial size of the direct mapping region. This is right in the > old code where __PHYSICAL_MASK_SHIFT was equal to MAX_PHYSMEM_BITS, > 46bit, and only 4-level mode was supported. > > Later, in commit: > b83ce5ee91471d ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52"), > __PHYSICAL_MASK_SHIFT was changed to be 52 always, no matter it's > 5-level or 4-level. This is wrong for 4-level paging. Then when > adapt phyiscal memory region size based on available memory, it > will overflow if the amount of system RAM and the padding is bigger > than 64TB. > > In fact, here MAX_PHYSMEM_BITS should be used instead. Fix it by > replacing __PHYSICAL_MASK_SHIFT with MAX_PHYSMEM_BITS. > > Fixes: b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52") > Signed-off-by: Baoquan He > Acked-by: Kirill A. Shutemov > Reviewed-by: Thomas Garnier So this changelog has a handful of problems: - there's a typo in the title - what does 'memory KASLR' mean? All KASLR deals with memory. - there's a typo in the second paragraph - Please punctuate more precisely: '64TB' is written as '64 TB' and '46bit' is written as '46 bits' - '52 always' is accurate but '52 bits always' would be more useful: write out units where appropriate to reduce ambiguity and parsing complexity of changelogs. Also, in this particular sentence it should be 'always 52 bits'. - s/when adapt /when we adapt - s/This is right in the old code /This is correct in the old code Thanks, Ingo