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[2003:d8:2f1a:3700:2982:b5f7:a04e:4cb4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4532e256b95sm60924015e9.30.2025.06.13.11.09.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 13 Jun 2025 11:09:43 -0700 (PDT) Message-ID: Date: Fri, 13 Jun 2025 20:09:41 +0200 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 5/5] vfio-pci: Best-effort huge pfnmaps with !MAP_FIXED mappings To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org Cc: Andrew Morton , Alex Williamson , Zi Yan , Jason Gunthorpe , Alex Mastro , Nico Pache References: <20250613134111.469884-1-peterx@redhat.com> <20250613134111.469884-6-peterx@redhat.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: <20250613134111.469884-6-peterx@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13.06.25 15:41, Peter Xu wrote: > This patch enables best-effort mmap() for vfio-pci bars even without > MAP_FIXED, so as to utilize huge pfnmaps as much as possible. It should > also avoid userspace changes (switching to MAP_FIXED with pre-aligned VA > addresses) to start enabling huge pfnmaps on VFIO bars. > > Here the trick is making sure the MMIO PFNs will be aligned with the VAs > allocated from mmap() when !MAP_FIXED, so that whatever returned from > mmap(!MAP_FIXED) of vfio-pci MMIO regions will be automatically suitable > for huge pfnmaps as much as possible. > > To achieve that, a custom vfio_device's get_unmapped_area() for vfio-pci > devices is needed. > > Note that MMIO physical addresses should normally be guaranteed to be > always bar-size aligned, hence the bar offset can logically be directly > used to do the calculation. However to make it strict and clear (rather > than relying on spec details), we still try to fetch the bar's physical > addresses from pci_dev.resource[]. > > Signed-off-by: Alex Williamson There is likely a Co-developed-by: Alex Williamson missing? > Signed-off-by: Peter Xu > --- > drivers/vfio/pci/vfio_pci.c | 3 ++ > drivers/vfio/pci/vfio_pci_core.c | 65 ++++++++++++++++++++++++++++++++ > include/linux/vfio_pci_core.h | 6 +++ > 3 files changed, 74 insertions(+) > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index 5ba39f7623bb..d9ae6cdbea28 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -144,6 +144,9 @@ static const struct vfio_device_ops vfio_pci_ops = { > .detach_ioas = vfio_iommufd_physical_detach_ioas, > .pasid_attach_ioas = vfio_iommufd_physical_pasid_attach_ioas, > .pasid_detach_ioas = vfio_iommufd_physical_pasid_detach_ioas, > +#ifdef CONFIG_ARCH_SUPPORTS_HUGE_PFNMAP > + .get_unmapped_area = vfio_pci_core_get_unmapped_area, > +#endif > }; > > static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id) > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 6328c3a05bcd..835bc168f8b7 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -1641,6 +1641,71 @@ static unsigned long vma_to_pfn(struct vm_area_struct *vma) > return (pci_resource_start(vdev->pdev, index) >> PAGE_SHIFT) + pgoff; > } > > +#ifdef CONFIG_ARCH_SUPPORTS_HUGE_PFNMAP > +/* > + * Hint function to provide mmap() virtual address candidate so as to be > + * able to map huge pfnmaps as much as possible. It is done by aligning > + * the VA to the PFN to be mapped in the specific bar. > + * > + * Note that this function does the minimum check on mmap() parameters to > + * make the PFN calculation valid only. The majority of mmap() sanity check > + * will be done later in mmap(). > + */ > +unsigned long vfio_pci_core_get_unmapped_area(struct vfio_device *device, > + struct file *file, > + unsigned long addr, > + unsigned long len, > + unsigned long pgoff, > + unsigned long flags) A very suboptimal way to indent this many parameters; just use two tabs at the beginning. > +{ > + struct vfio_pci_core_device *vdev = > + container_of(device, struct vfio_pci_core_device, vdev); > + struct pci_dev *pdev = vdev->pdev; > + unsigned long ret, phys_len, req_start, phys_addr; > + unsigned int index; > + > + index = pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT); Could do unsigned int index = pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT); at the very top. > + > + /* Currently, only bars 0-5 supports huge pfnmap */ > + if (index >= VFIO_PCI_ROM_REGION_INDEX) > + goto fallback; > + > + /* Bar offset */ > + req_start = (pgoff << PAGE_SHIFT) & ((1UL << VFIO_PCI_OFFSET_SHIFT) - 1); > + phys_len = PAGE_ALIGN(pci_resource_len(pdev, index)); > + > + /* > + * Make sure we at least can get a valid physical address to do the > + * math. If this happens, it will probably fail mmap() later.. > + */ > + if (req_start >= phys_len) > + goto fallback; > + > + phys_len = MIN(phys_len, len); > + /* Calculate the start of physical address to be mapped */ > + phys_addr = pci_resource_start(pdev, index) + req_start; > + > + /* Choose the alignment */ > + if (IS_ENABLED(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP) && phys_len >= PUD_SIZE) { > + ret = mm_get_unmapped_area_aligned(file, addr, len, phys_addr, > + flags, PUD_SIZE, 0); > + if (ret) > + return ret; > + } > + > + if (phys_len >= PMD_SIZE) { > + ret = mm_get_unmapped_area_aligned(file, addr, len, phys_addr, > + flags, PMD_SIZE, 0); > + if (ret) > + return ret; Similar to Jason, I wonder if that logic should reside in the core, and we only indicate the maximum page table level we support. unsigned int order) > { > diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h > index fbb472dd99b3..e59699e01901 100644 > --- a/include/linux/vfio_pci_core.h > +++ b/include/linux/vfio_pci_core.h > @@ -119,6 +119,12 @@ ssize_t vfio_pci_core_read(struct vfio_device *core_vdev, char __user *buf, > size_t count, loff_t *ppos); > ssize_t vfio_pci_core_write(struct vfio_device *core_vdev, const char __user *buf, > size_t count, loff_t *ppos); > +unsigned long vfio_pci_core_get_unmapped_area(struct vfio_device *device, > + struct file *file, > + unsigned long addr, > + unsigned long len, > + unsigned long pgoff, > + unsigned long flags); Dito. -- Cheers, David / dhildenb