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Received: from 30.221.98.53(mailfrom:ethan.xys@linux.alibaba.com fp:SMTPD_---0W1PkVY5_1709120113) by smtp.aliyun-inc.com; Wed, 28 Feb 2024 19:35:14 +0800 Message-ID: <4ec89335-917a-4ea5-b38b-5cea6476d9a1@linux.alibaba.com> Date: Wed, 28 Feb 2024 19:35:12 +0800 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] vfio/type1: unpin PageReserved page To: David Hildenbrand , Alex Williamson , akpm@linux-foundation.org Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240226160106.24222-1-ethan.xys@linux.alibaba.com> <20240226091438.1fc37957.alex.williamson@redhat.com> <20240226103238.75ad4b24.alex.williamson@redhat.com> From: Yisheng Xie In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2024/2/27 18:27, David Hildenbrand 写道: > On 26.02.24 18:32, Alex Williamson wrote: >> On Tue, 27 Feb 2024 01:14:54 +0800 >> Yisheng Xie wrote: >> >>> 在 2024/2/27 00:14, Alex Williamson 写道: >>>> On Tue, 27 Feb 2024 00:01:06 +0800 >>>> Yisheng Xie  wrote: >>>>> We meet a warning as following: >>>>>    WARNING: CPU: 99 PID: 1766859 at mm/gup.c:209 >>>>> try_grab_page.part.0+0xe8/0x1b0 >>>>>    CPU: 99 PID: 1766859 Comm: qemu-kvm Kdump: loaded Tainted: GOE  >>>>> 5.10.134-008.2.x86_64 #1 >>>> ^^^^^^^^ >>>> >>>> Does this issue reproduce on mainline?  Thanks, >>> >>> I have check the code of mainline, the logical seems the same as my >>> version. >>> >>> so I think it can reproduce if i understand correctly. >> >> I obviously can't speak to what's in your 5.10.134-008.2 kernel, but I >> do know there's a very similar issue resolved in v6.0 mainline and >> included in v5.10.146 of the stable tree.  Please test.  Thanks, > > This commit, to be precise: > > commit 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4 > Author: Alex Williamson > Date:   Mon Aug 29 21:05:40 2022 -0600 > >     vfio/type1: Unpin zero pages >         There's currently a reference count leak on the zero page.  We > increment >     the reference via pin_user_pages_remote(), but the page is later > handled >     as an invalid/reserved page, therefore it's not accounted against the >     user and not unpinned by our put_pfn(). >         Introducing special zero page handling in put_pfn() would > resolve the >     leak, but without accounting of the zero page, a single user could >     still create enough mappings to generate a reference count overflow. >         The zero page is always resident, so for our purposes there's > no reason >     to keep it pinned.  Therefore, add a loop to walk pages returned from >     pin_user_pages_remote() and unpin any zero pages. > > > BUT > > in the meantime, we also have > > commit c8070b78751955e59b42457b974bea4a4fe00187 > Author: David Howells > Date:   Fri May 26 22:41:40 2023 +0100 > >     mm: Don't pin ZERO_PAGE in pin_user_pages() >         Make pin_user_pages*() leave a ZERO_PAGE unpinned if it > extracts a pointer >     to it from the page tables and make unpin_user_page*() > correspondingly >     ignore a ZERO_PAGE when unpinning.  We don't want to risk > overrunning a >     zero page's refcount as we're only allowed ~2 million pins on it - >     something that userspace can conceivably trigger. >         Add a pair of functions to test whether a page or a folio is a > ZERO_PAGE. > > > So the unpin_user_page_* won't do anything with the shared zeropage. > > (likely, we could revert 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4) Thanks for your detail info. BTW, do we need handle all of the pagereserved page?