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(p200300cbc7435500a9bd94ab74e9782f.dip0.t-ipconnect.de. [2003:cb:c743:5500:a9bd:94ab:74e9:782f]) by smtp.gmail.com with ESMTPSA id gw18-20020a05600c851200b004030c778396sm3452549wmb.4.2023.09.11.01.09.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Sep 2023 01:09:46 -0700 (PDT) Message-ID: Date: Mon, 11 Sep 2023 10:09:44 +0200 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH 3/3] /dev/mem: Do not map unaccepted memory To: Dave Hansen , "Kirill A. Shutemov" Cc: Adrian Hunter , Borislav Petkov , Andrew Morton , 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 References: <20230906073902.4229-1-adrian.hunter@intel.com> <20230906073902.4229-4-adrian.hunter@intel.com> <9ffb7a3b-cf20-617a-e4f1-8a6a8a2c5972@intel.com> <20230907142510.vcj57cvnewqt4m37@box.shutemov.name> <7a50d04f-63ee-a901-6f39-7d341e423a77@intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <7a50d04f-63ee-a901-6f39-7d341e423a77@intel.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07.09.23 16:46, Dave Hansen wrote: > On 9/7/23 07:25, Kirill A. Shutemov wrote: >> On Thu, Sep 07, 2023 at 07:15:21AM -0700, Dave Hansen wrote: >>> On 9/6/23 00:39, 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. >>> Doesn't /dev/mem already provide a billion ways for someone to shoot >>> themselves in the foot? TDX seems to have added the 1,000,000,001st. >>> Is this really worth patching? >> Is it better to let TD die silently? I don't think so. > > First, let's take a look at all of the distro kernels that folks will > run under TDX. Do they have STRICT_DEVMEM set? For virtio-mem, we do config VIRTIO_MEM ... depends on EXCLUSIVE_SYSTEM_RAM Which in turn: config EXCLUSIVE_SYSTEM_RAM ... depends on !DEVMEM || STRICT_DEVMEM Not supported on all archs, but at least on RHEL9 on x86_64 and aarch64. So, making unaccepted memory similarly depend on "!DEVMEM || STRICT_DEVMEM" does not sound too far off ... -- Cheers, David / dhildenb