From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christopher Lameter Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Date: Tue, 29 Oct 2019 07:08:42 +0000 (UTC) Message-ID: References: <1572171452-7958-1-git-send-email-rppt@kernel.org> <1572171452-7958-2-git-send-email-rppt@kernel.org> <20191028123124.ogkk5ogjlamvwc2s@box> <20191028130018.GA7192@rapoport-lnx> <20191028131623.zwuwguhm4v4s5imh@box> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <20191028131623.zwuwguhm4v4s5imh@box> Sender: linux-kernel-owner@vger.kernel.org To: "Kirill A. Shutemov" Cc: Mike Rapoport , linux-kernel@vger.kernel.org, Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Dave Hansen , James Bottomley , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-api@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, Mike Rapoport List-Id: linux-api@vger.kernel.org On Mon, 28 Oct 2019, Kirill A. Shutemov wrote: > Setting a single 4k page non-present in the direct mapping will require > splitting 2M or 1G page we usually map direct mapping with. And it's one > way road. We don't have any mechanism to map the memory with huge page > again after the application has freed the page. > > It might be okay if all these pages cluster together, but I don't think we > have a way to achieve it easily. Set aside a special physical memory range for this and migrate the page to that physical memory range when MAP_EXCLUSIVE is specified? Maybe some processors also have hardware ranges that offer additional protection for stuff like that?