From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (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 D9C13947E for ; Wed, 24 Apr 2024 03:23:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713929026; cv=none; b=O/ZDJaLEFvKtE9qmuRTHQNQquSKyHtLg5CXN7tATwNdWXjXksHDtxPJB+xjEWrvr23Ya5FGvzZwBDzXsGgyw8faP98xwLskhBkijdIAcB+I40yHg687WH19/CmNevMXSnH6kqsKyNlHsB235U/tFpwypYmTbF1d4eJ3bEIP5pzw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713929026; c=relaxed/simple; bh=nSSuh1T9ImcHRaH8apSL1rAEpx5DhaOz29wKwH5gzrA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JldbSpYJEguz33Kv6zyt79viiJYNcpYBBF+14Jex31/e4llNXQYxIBI3gqWoHcu+MLlHqji8A8Zc7RKg+8W5msFws0nPITh+BvRi8jXTazVjUtON2Fx1JrE/bPDkEdpBh1ZgJouv13wFMIv+oV3uAE4m+oxmelPhldrudOzOdaM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=ewLyDrez; arc=none smtp.client-ip=115.124.30.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="ewLyDrez" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1713929020; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=32ZNU58IYfy83wAR8NxM0IwKi6rLOoazzzTunUN4tFw=; b=ewLyDrez+edy8bY0c4+9scNLmH0X07LaUqrSiD7aKP8sH1QvPSnATQ7vVPZhlxq1vomKMHCTgP1rNDUhLDSml1BxE5nTCoH4caxk2VVMzlA7XWE1IGDBu6Zfwd9Zk33SMq22njYJIe5Z+B3gQJn5+jUN/bkn1aRPBSzVns03nw0= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R471e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033068173054;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=12;SR=0;TI=SMTPD_---0W5AogkY_1713929017; Received: from 30.97.56.58(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W5AogkY_1713929017) by smtp.aliyun-inc.com; Wed, 24 Apr 2024 11:23:38 +0800 Message-ID: Date: Wed, 24 Apr 2024 11:23:36 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/5] mm: memory: extend finish_fault() to support large folio To: Ryan Roberts , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, david@redhat.com, wangkefeng.wang@huawei.com, 21cnbao@gmail.com, ying.huang@intel.com, shy828301@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <358aefb1858b63164894d7d8504f3dae0b495366.1713755580.git.baolin.wang@linux.alibaba.com> <6aa25e2a-a6b6-4ab7-8300-053ca3c0d748@arm.com> From: Baolin Wang In-Reply-To: <6aa25e2a-a6b6-4ab7-8300-053ca3c0d748@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2024/4/23 19:03, Ryan Roberts wrote: > On 22/04/2024 08:02, Baolin Wang wrote: >> Add large folio mapping establishment support for finish_fault() as a preparation, >> to support multi-size THP allocation of anonymous shared pages in the following >> patches. >> >> Signed-off-by: Baolin Wang >> --- >> mm/memory.c | 25 ++++++++++++++++++------- >> 1 file changed, 18 insertions(+), 7 deletions(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index b6fa5146b260..094a76730776 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -4766,7 +4766,10 @@ vm_fault_t finish_fault(struct vm_fault *vmf) >> { >> struct vm_area_struct *vma = vmf->vma; >> struct page *page; >> + struct folio *folio; >> vm_fault_t ret; >> + int nr_pages, i; >> + unsigned long addr; >> >> /* Did we COW the page? */ >> if ((vmf->flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) >> @@ -4797,22 +4800,30 @@ vm_fault_t finish_fault(struct vm_fault *vmf) >> return VM_FAULT_OOM; >> } >> >> + folio = page_folio(page); >> + nr_pages = folio_nr_pages(folio); >> + addr = ALIGN_DOWN(vmf->address, nr_pages * PAGE_SIZE); > > I'm not sure this is safe. IIUC, finish_fault() is called for any file-backed > mapping. So you could have a situation where part of a (regular) file is mapped > in the process, faults and hits in the pagecache. But the folio returned by the > pagecache is bigger than the portion that the process has mapped. So you now end > up mapping beyond the VMA limits? In the pagecache case, you also can't assume > that the folio is naturally aligned in virtual address space. Good point. Yes, I think you are right, I need consider the VMA limits, and I should refer to the calculations of the start pte and end pte in do_fault_around(). >> vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, >> - vmf->address, &vmf->ptl); >> + addr, &vmf->ptl); >> if (!vmf->pte) >> return VM_FAULT_NOPAGE; >> >> /* Re-check under ptl */ >> - if (likely(!vmf_pte_changed(vmf))) { >> - struct folio *folio = page_folio(page); >> - >> - set_pte_range(vmf, folio, page, 1, vmf->address); >> - ret = 0; >> - } else { >> + if (nr_pages == 1 && vmf_pte_changed(vmf)) { >> update_mmu_tlb(vma, vmf->address, vmf->pte); >> ret = VM_FAULT_NOPAGE; >> + goto unlock; >> + } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) { > > I think you have grabbed this from do_anonymous_page()? But I'm not sure it > works in the same way here as it does there. For the anon case, if userfaultfd > is armed, alloc_anon_folio() will only ever allocate order-0. So we end up in IMO, the userfaultfd validation should do in the vma->vm_ops->fault() callback, to make sure the nr_pages is always 1 if userfaultfd is armed. > the vmf_pte_changed() path, which will allow overwriting a uffd entry. But here, > there is nothing stopping nr_pages being greater than 1 when there could be a > uffd entry present, and you will fail due to the pte_range_none() check. (see > pte_marker_handle_uffd_wp()). So if we do the userfaultfd validation in ->fault() callback, then here we can use the same logic as with anonymous case.