lkml.org 
[lkml]   [2021]   [Mar]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Subject答复: [PATCH] vfio/pci: make the vfio pci mma p fault reentrant
Date
Hi Alex:

> -----邮件原件-----
> 发件人: Alex Williamson [mailto:alex.williamson@redhat.com]
> 发送时间: 2021年3月10日 14:09
> 收件人: Jason Gunthorpe <jgg@nvidia.com>
> 抄送: Peter Xu <peterx@redhat.com>; Zengtao (B) <prime.zeng@hisilicon.com>;
> Cornelia Huck <cohuck@redhat.com>; Kevin Tian <kevin.tian@intel.com>;
> Andrew Morton <akpm@linux-foundation.org>; Giovanni Cabiddu
> <giovanni.cabiddu@intel.com>; Michel Lespinasse <walken@google.com>; Jann
> Horn <jannh@google.com>; Max Gurtovoy <mgurtovoy@nvidia.com>;
> kvm@vger.kernel.org; linux-kernel@vger.kernel.org; Linuxarm
> <linuxarm@huawei.com>
> 主题: Re: [PATCH] vfio/pci: make the vfio_pci_mmap_fault reentrant
>
> On Tue, 9 Mar 2021 19:41:27 -0400
> Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> > On Tue, Mar 09, 2021 at 12:26:07PM -0700, Alex Williamson wrote:
> >
> > > In the new series, I think the fault handler becomes (untested):
> > >
> > > 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;
> > > unsigned long base_pfn, pgoff;
> > > vm_fault_t ret = VM_FAULT_SIGBUS;
> > >
> > > if (vfio_pci_bar_vma_to_pfn(vma, &base_pfn))
> > > return ret;
> > >
> > > pgoff = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
> >
> > I don't think this math is completely safe, it needs to parse the
> > vm_pgoff..
> >
> > I'm worried userspace could split/punch/mangle a VMA using
> > munmap/mremap/etc/etc in a way that does update the pg_off but is
> > incompatible with the above.
>
> parsing vm_pgoff is done in:
>
> static int vfio_pci_bar_vma_to_pfn(struct vm_area_struct *vma,
> unsigned long *pfn) {
> struct vfio_pci_device *vdev = vma->vm_private_data;
> struct pci_dev *pdev = vdev->pdev;
> int index;
> u64 pgoff;
>
> index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
>
> if (index >= VFIO_PCI_ROM_REGION_INDEX ||
> !vdev->bar_mmap_supported[index] || !vdev->barmap[index])
> return -EINVAL;
>
> pgoff = vma->vm_pgoff &
> ((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
>
> *pfn = (pci_resource_start(pdev, index) >> PAGE_SHIFT) + pgoff;
>
> return 0;
> }
>
> But given Peter's concern about faulting individual pages, I think the fault handler
> becomes:
>
> 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;
> unsigned long vaddr, pfn;
> vm_fault_t ret = VM_FAULT_SIGBUS;
>
> if (vfio_pci_bar_vma_to_pfn(vma, &pfn))
> return ret;
>
> down_read(&vdev->memory_lock);
>
> if (__vfio_pci_memory_enabled(vdev)) {
> for (vaddr = vma->vm_start;
> vaddr < vma->vm_end; vaddr += PAGE_SIZE, pfn++) {
One concern here is the performance, since you are doing the mapping for the
whole vma, what about using block mapping if applicable?

> ret = vmf_insert_pfn_prot(vma, vaddr, pfn,
>
> pgprot_decrypted(vma->vm_page_prot));
> if (ret != VM_FAULT_NOPAGE) {
> zap_vma_ptes(vma, vma->vm_start,
> vaddr - vma->vm_start);
> break;
> }
> }
> }
>
> up_read(&vdev->memory_lock);
>
> return ret;
> }
>
> Thanks,
> Alex
\
 
 \ /
  Last update: 2021-03-11 04:34    [W:0.071 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site