From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B52F2238C1B; Mon, 24 Nov 2025 11:05:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763982326; cv=none; b=NoCH5/7mbILmqS2wDRuhtd9ojTDGzK0bgDx67I8D9Xzy2W1BVxC/g+7wQNSAzCcNKt/sVd2Rxee0S4H920jIAPPnZjZ2Ql2eKhmfapPq3o56Fs+UBQo6L1TzIedo/I0NMKDWkgDgYNwDMD9vmpgZv3zuzwfYbFZvjxLmIIx9VK4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763982326; c=relaxed/simple; bh=xAo9jDsdZnz6/lhNhkcTyH2Vv9bCshFd2rXVbo51big=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GFu9xy9KTkVVSm9Mp6d5HuibRPuy2hK62CzB3/F+lnlPGfgreSkmTggGzUIs/Y5Ff3zFDSzdl2Utja29Ymn4UUzX9uLlxxGKowViPbAsEk67ctWpkgyq61ffwm4QTzigVj/M6a0MHd3wAh1qnp6bT0OdQoSUvG1W2nAKLMsBaG8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NdHaKGWS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NdHaKGWS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 38170C4CEF1; Mon, 24 Nov 2025 11:05:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763982326; bh=xAo9jDsdZnz6/lhNhkcTyH2Vv9bCshFd2rXVbo51big=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=NdHaKGWS1O+C+KbtPyPToMXSoUWgmsYqnLDc2FhNyH96nyxbQtDe7ZubKu/lLjdyC X8ObCLyrQMQeU6tEylmtcRhWaISmSavumTsxfODA1Ru0XfV5JKiZ/cWHOJVJCtQ2Qn yxnSveJJgYC/h67AQ94ObFQ2vSxyQvGr9n/+Xhjy8txtI5PsMxzLEZnNAsSAWl53hB ojehVEENSrvjdmIw3jzSxpHDTX7Q+YzWt9pp8X+mZ4Pz//V3guYCyY8h1bxIEjayso LNYh72Ti4ciAh1xh2f1z4kcJCDXd8y6VKCB4scGUKFphVaz8NWAhND6uGKkjYepnzw ozLNRwume7YGA== Message-ID: Date: Mon, 24 Nov 2025 12:05:18 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] mm: introduce VM_FAULT_UFFD_MINOR fault reason To: Mike Rapoport , linux-mm@kvack.org Cc: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Nikita Kalyazin , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20251123102707.559422-1-rppt@kernel.org> <20251123102707.559422-4-rppt@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251123102707.559422-4-rppt@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/23/25 11:27, Mike Rapoport wrote: > From: "Mike Rapoport (Microsoft)" > > When a VMA is registered with userfaulfd in minor mode, its ->fault() > method should check if a folio exists in the page cache and if yes > ->fault() should call handle_userfault(VM_UFFD_MISSING). > > Instead of calling handle_userfault() directly from a specific ->fault() > implementation introduce new fault reason VM_FAULT_UFFD_MINOR that will > notify the core page fault handler that it should call > handle_userfaultfd(VM_UFFD_MISSING) to complete a page fault. > > Replace a call to handle_userfault(VM_UFFD_MISSING) in shmem and use the > new VM_FAULT_UFFD_MINOR there instead. > > Suggested-by: David Hildenbrand (Red Hat) > Signed-off-by: Mike Rapoport (Microsoft) > --- > include/linux/mm_types.h | 3 +++ > mm/memory.c | 2 ++ > mm/shmem.c | 2 +- > 3 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 90e5790c318f..eb135369940f 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -1523,6 +1523,8 @@ typedef __bitwise unsigned int vm_fault_t; > * fsync() to complete (for synchronous page faults > * in DAX) > * @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock released > + * @VM_FAULT_UFFD_MINOR: ->fault did not modify page tables and needs > + * handle_userfault(VM_UFFD_MINOR) to complete > * @VM_FAULT_HINDEX_MASK: mask HINDEX value > * > */ > @@ -1540,6 +1542,7 @@ enum vm_fault_reason { > VM_FAULT_DONE_COW = (__force vm_fault_t)0x001000, > VM_FAULT_NEEDDSYNC = (__force vm_fault_t)0x002000, > VM_FAULT_COMPLETED = (__force vm_fault_t)0x004000, > + VM_FAULT_UFFD_MINOR = (__force vm_fault_t)0x008000, > VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000, > }; > > diff --git a/mm/memory.c b/mm/memory.c > index b59ae7ce42eb..94acbac8cefb 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5279,6 +5279,8 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) > } > > ret = vma->vm_ops->fault(vmf); > + if (unlikely(ret & VM_FAULT_UFFD_MINOR)) > + return handle_userfault(vmf, VM_UFFD_MINOR); If we could define VM_FAULT_UFFD_MINOR to be 0 without USERFAULTFD, we could optimize that check out completely on such configs. -- Cheers David