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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 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 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 4ABD2C0002 X-Stat-Signature: 8sbjo53ng7rnptpbixkmixddzjft9oa9 X-HE-Tag: 1713929022-945399 X-HE-Meta: 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 Lcg== 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: List-Subscribe: List-Unsubscribe: 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.