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Shutemov" To: Adrian Hunter Cc: Borislav Petkov , Andrew Morton , Dave Hansen , Vlastimil Babka , Mike Rapoport , Lorenzo Stoakes , Tom Lendacky , Baoquan He , Vivek Goyal , Dave Young , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, kexec@lists.infradead.org Subject: Re: [PATCH 3/3] /dev/mem: Do not map unaccepted memory Message-ID: <20230907100614.35mxxo63xwkz7ohw@box.shutemov.name> References: <20230906073902.4229-1-adrian.hunter@intel.com> <20230906073902.4229-4-adrian.hunter@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230906073902.4229-4-adrian.hunter@intel.com> X-Rspamd-Queue-Id: AAD6B140029 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 6px75cu1fr6ytx3pmqf3xasu6gk1pa9p X-HE-Tag: 1694081199-873286 X-HE-Meta: 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 zLp+XaeD 7E7OTZHkZcbmWFRtVhly+8lWH+rMQdjseEQvo0HbQASv86m7nhCs4IrVkFnGMypyNXYXIhZDH4X3Vsdr/mN5r2eCD7dt0IRrIhswJ6aW5jOST0Is= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Sep 06, 2023 at 10:39:02AM +0300, Adrian Hunter wrote: > Support for unaccepted memory was added recently, refer commit > dcdfdd40fa82 ("mm: Add support for unaccepted memory"), whereby > a virtual machine may need to accept memory before it can be used. > > Do not map unaccepted memory because it can cause the guest to fail. > > For /dev/mem, this means a read of unaccepted memory will return zeros, > a write to unaccepted memory will be ignored, but an mmap of unaccepted > memory will return an error. I am unsure who currently uses /dev/mem. The change to the mmap path has the potential to cause issues as it is a new behavior. However, it appears to be a common practice as we also fail to mmap if PAT is set on a page in the rang. I suppose it is acceptable. Another option is to accept the memory on mmap, but it seems excessive at this point. -- Kiryl Shutsemau / Kirill A. Shutemov