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[142.68.57.212]) by smtp.gmail.com with ESMTPSA id b126sm3768601qkc.119.2020.05.01.16.25.51 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Fri, 01 May 2020 16:25:51 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1jUf2U-0005Rh-Ld; Fri, 01 May 2020 20:25:50 -0300 Date: Fri, 1 May 2020 20:25:50 -0300 From: Jason Gunthorpe To: Alex Williamson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, cohuck@redhat.com, peterx@redhat.com Subject: Re: [PATCH 2/3] vfio-pci: Fault mmaps to enable vma tracking Message-ID: <20200501232550.GP26002@ziepe.ca> References: <158836742096.8433.685478071796941103.stgit@gimli.home> <158836915917.8433.8017639758883869710.stgit@gimli.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <158836915917.8433.8017639758883869710.stgit@gimli.home> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, May 01, 2020 at 03:39:19PM -0600, Alex Williamson wrote: > Rather than calling remap_pfn_range() when a region is mmap'd, setup > a vm_ops handler to support dynamic faulting of the range on access. > This allows us to manage a list of vmas actively mapping the area that > we can later use to invalidate those mappings. The open callback > invalidates the vma range so that all tracking is inserted in the > fault handler and removed in the close handler. > > Signed-off-by: Alex Williamson > --- > drivers/vfio/pci/vfio_pci.c | 76 ++++++++++++++++++++++++++++++++++- > drivers/vfio/pci/vfio_pci_private.h | 7 +++ > 2 files changed, 81 insertions(+), 2 deletions(-) > +static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf) > +{ > + struct vm_area_struct *vma = vmf->vma; > + struct vfio_pci_device *vdev = vma->vm_private_data; > + > + if (vfio_pci_add_vma(vdev, vma)) > + return VM_FAULT_OOM; > + > + if (remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, > + vma->vm_end - vma->vm_start, vma->vm_page_prot)) > + return VM_FAULT_SIGBUS; > + > + return VM_FAULT_NOPAGE; > +} > + > +static const struct vm_operations_struct vfio_pci_mmap_ops = { > + .open = vfio_pci_mmap_open, > + .close = vfio_pci_mmap_close, > + .fault = vfio_pci_mmap_fault, > +}; > + > static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) > { > struct vfio_pci_device *vdev = device_data; > @@ -1357,8 +1421,14 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma) > vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > vma->vm_pgoff = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff; > > - return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, > - req_len, vma->vm_page_prot); > + /* > + * See remap_pfn_range(), called from vfio_pci_fault() but we can't > + * change vm_flags within the fault handler. Set them now. > + */ > + vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP; > + vma->vm_ops = &vfio_pci_mmap_ops; Perhaps do the vfio_pci_add_vma & remap_pfn_range combo here if the BAR is activated ? That way a fully populated BAR is presented in the common case and avoids taking a fault path? But it does seem OK as is Jason