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[2003:cb:c748:ba00:1c00:48ea:7b5a:c12b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4217d7f9a6esm112449155e9.48.2024.06.11.07.13.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Jun 2024 07:13:49 -0700 (PDT) Message-ID: Date: Tue, 11 Jun 2024 16:13:47 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] s390/pci: Fix s390_mmio_read/write syscall page fault handling To: Niklas Schnelle , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Alex Williamson , Gerd Bayer , Matthew Rosato , Jason Gunthorpe Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <20240529-vfio_pci_mmap-v3-0-cd217d019218@linux.ibm.com> <20240529-vfio_pci_mmap-v3-1-cd217d019218@linux.ibm.com> <98de56b1ba37f51639b9a2c15a745e19a45961a0.camel@linux.ibm.com> <30ecb17b7a3414aeb605c51f003582c7f2cf6444.camel@linux.ibm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11.06.24 15:23, Niklas Schnelle wrote: > On Tue, 2024-06-11 at 14:08 +0200, Niklas Schnelle wrote: >> On Tue, 2024-06-11 at 13:21 +0200, Niklas Schnelle wrote: >>> On Wed, 2024-05-29 at 13:36 +0200, Niklas Schnelle wrote: >>>> The s390 MMIO syscalls when using the classic PCI instructions do not >>>> cause a page fault when follow_pte() fails due to the page not being >>>> present. Besides being a general deficiency this breaks vfio-pci's mmap() >>>> handling once VFIO_PCI_MMAP gets enabled as this lazily maps on first >>>> access. Fix this by following a failed follow_pte() with >>>> fixup_user_page() and retrying the follow_pte(). >>>> >>>> Reviewed-by: Jason Gunthorpe >>>> Reviewed-by: Matthew Rosato >>>> Signed-off-by: Niklas Schnelle >>>> --- >>>> arch/s390/pci/pci_mmio.c | 18 +++++++++++++----- >>>> 1 file changed, 13 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c >>>> index 5398729bfe1b..80c21b1a101c 100644 >>>> --- a/arch/s390/pci/pci_mmio.c >>>> +++ b/arch/s390/pci/pci_mmio.c >>>> @@ -170,8 +170,12 @@ SYSCALL_DEFINE3(s390_pci_mmio_write, unsigned long, mmio_addr, >>>> goto out_unlock_mmap; >>>> >>>> ret = follow_pte(vma, mmio_addr, &ptep, &ptl); >>>> - if (ret) >>>> - goto out_unlock_mmap; >>>> + if (ret) { >>>> + fixup_user_fault(current->mm, mmio_addr, FAULT_FLAG_WRITE, NULL); >>>> + ret = follow_pte(vma, mmio_addr, &ptep, &ptl); >>>> + if (ret) >>>> + goto out_unlock_mmap; >>>> + } >>>> >>>> io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) | >>>> (mmio_addr & ~PAGE_MASK)); >>>> @@ -305,12 +309,16 @@ SYSCALL_DEFINE3(s390_pci_mmio_read, unsigned long, mmio_addr, >>>> if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) >>>> goto out_unlock_mmap; >>>> ret = -EACCES; >>>> - if (!(vma->vm_flags & VM_WRITE)) >>>> + if (!(vma->vm_flags & VM_READ)) >>>> goto out_unlock_mmap; >>>> >>>> ret = follow_pte(vma, mmio_addr, &ptep, &ptl); >>>> - if (ret) >>>> - goto out_unlock_mmap; >>>> + if (ret) { >>>> + fixup_user_fault(current->mm, mmio_addr, 0, NULL); >>>> + ret = follow_pte(vma, mmio_addr, &ptep, &ptl); >>>> + if (ret) >>>> + goto out_unlock_mmap; >>>> + } >>>> >>>> io_addr = (void __iomem *)((pte_pfn(*ptep) << PAGE_SHIFT) | >>>> (mmio_addr & ~PAGE_MASK)); >>>> >>> >>> Ughh, I think I just stumbled over a problem with this. This is a >>> failing lock held assertion via __is_vma_write_locked() in >>> remap_pfn_range_notrack() but I'm not sure yet what exactly causes this >>> >>> [ 67.338855] ------------[ cut here ]------------ >>> [ 67.338865] WARNING: CPU: 15 PID: 2056 at include/linux/rwsem.h:85 remap_pfn_range_notrack+0x596/0x5b0 >>> [ 67.338874] Modules linked in: <--- 8< ---> >>> [ 67.338931] CPU: 15 PID: 2056 Comm: vfio-test Not tainted 6.10.0-rc1-pci-pfault-00004-g193e3a513cee #5 >>> [ 67.338934] Hardware name: IBM 3931 A01 701 (LPAR) >>> [ 67.338935] Krnl PSW : 0704c00180000000 000003e54c9730ea (remap_pfn_range_notrack+0x59a/0x5b0) >>> [ 67.338940] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3 >>> [ 67.338944] Krnl GPRS: 0000000000000100 000003655915fb78 000002d80b9a5928 000003ff7fa00000 >>> [ 67.338946] 0004008000000000 0000000000004000 0000000000000711 000003ff7fa04000 >>> [ 67.338948] 000002d80c533f00 000002d800000100 000002d81bbe6c28 000002d80b9a5928 >>> [ 67.338950] 000003ff7fa00000 000002d80c533f00 000003e54c973120 000003655915fab0 >>> [ 67.338956] Krnl Code: 000003e54c9730de: a708ffea lhi %r0,-22 >>> 000003e54c9730e2: a7f4fff6 brc 15,000003e54c9730ce >>> #000003e54c9730e6: af000000 mc 0,0 >>> >000003e54c9730ea: a7f4fd6e brc 15,000003e54c972bc6 >>> 000003e54c9730ee: af000000 mc 0,0 >>> 000003e54c9730f2: af000000 mc 0,0 >>> 000003e54c9730f6: 0707 bcr 0,%r7 >>> 000003e54c9730f8: 0707 bcr 0,%r7 >>> [ 67.339025] Call Trace: >>> [ 67.339027] [<000003e54c9730ea>] remap_pfn_range_notrack+0x59a/0x5b0 >>> [ 67.339032] [<000003e54c973120>] remap_pfn_range+0x20/0x30 >>> [ 67.339035] [<000003e4cce5396c>] vfio_pci_mmap_fault+0xec/0x1d0 [vfio_pci_core] >>> [ 67.339043] [<000003e54c977240>] handle_mm_fault+0x6b0/0x25a0 >>> [ 67.339046] [<000003e54c966328>] fixup_user_fault+0x138/0x310 >>> [ 67.339048] [<000003e54c63a91c>] __s390x_sys_s390_pci_mmio_read+0x28c/0x3a0 >>> [ 67.339051] [<000003e54c5e200a>] do_syscall+0xea/0x120 >>> [ 67.339055] [<000003e54d5f9954>] __do_syscall+0x94/0x140 >>> [ 67.339059] [<000003e54d611020>] system_call+0x70/0xa0 >>> [ 67.339063] Last Breaking-Event-Address: >>> [ 67.339065] [<000003e54c972bc2>] remap_pfn_range_notrack+0x72/0x5b0 >>> [ 67.339067] ---[ end trace 0000000000000000 ]--- >>> >> >> This has me a bit confused so far as __is_vma_write_locked() checks >> mmap_assert_write_locked(vma->vm_mm) but most other users of >> fixup_user_fault() hold mmap_read_lock() just like this code and >> clearly in the non page fault case we only need the read lock. This is likely the vm_flags_set()->vma_start_write(vma)->__is_vma_write_locked() which checks mmap_assert_write_locked(). Setting VMA flags would be racy with the mmap lock in read mode. remap_pfn_range() documents: "this is only safe if the mm semaphore is held when called." which doesn't spell out if it needs to be held in write mode (which I think it does) :) My best guess is: if you are using remap_pfn_range() from a fault handler (not during mmap time) you are doing something wrong, that's why you get that report. vmf_insert_pfn() and friends might be better alternatives, that make sure that the VMA already received the proper VMA flags at mmap time. >> > > And it gets weirder, as I could have sworn that I properly tested this > on v1, I retested with v1 (tags/sent/vfio_pci_mmap-v1 on my > git.kernel.org/niks and based on v6.9) and there I don't get the above > warning. I also made sure that it's not caused by my change to > "current->mm" for v2. But I'm also not hitting the checks David moved > into follow_pte() so yeah not sure what's going on here. You mean the mmap_assert_locked()? Yeah, that only checks if you have it in read mode, but not in write mode. -- Cheers, David / dhildenb