diff options
author | Paolo Bonzini <pbonzini@redhat.com> | 2016-06-07 18:51:18 +0300 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-07-05 15:41:26 +0300 |
commit | add6a0cd1c5ba51b201e1361b05a5df817083618 (patch) | |
tree | deda6470d77bbc8b478f4d508927754e8ff38e42 | |
parent | 92176a8ede577d0ff78ab3298e06701f67ad5f51 (diff) | |
download | linux-add6a0cd1c5ba51b201e1361b05a5df817083618.tar.xz |
KVM: MMU: try to fix up page faults before giving up
The vGPU folks would like to trap the first access to a BAR by setting
vm_ops on the VMAs produced by mmap-ing a VFIO device. The fault handler
then can use remap_pfn_range to place some non-reserved pages in the VMA.
This kind of VM_PFNMAP mapping is not handled by KVM, but follow_pfn
and fixup_user_fault together help supporting it. The patch also supports
VM_MIXEDMAP vmas where the pfns are not reserved and thus subject to
reference counting.
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Tested-by: Neo Jia <cjia@nvidia.com>
Reported-by: Kirti Wankhede <kwankhede@nvidia.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r-- | mm/gup.c | 1 | ||||
-rw-r--r-- | virt/kvm/kvm_main.c | 45 |
2 files changed, 43 insertions, 3 deletions
@@ -720,6 +720,7 @@ retry: } return 0; } +EXPORT_SYMBOL_GPL(fixup_user_fault); static __always_inline long __get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm, diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 5aae59e00bef..154b9ab459b0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1446,9 +1446,45 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, unsigned long addr, bool *async, bool write_fault, kvm_pfn_t *p_pfn) { - *p_pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + - vma->vm_pgoff; - BUG_ON(!kvm_is_reserved_pfn(*p_pfn)); + unsigned long pfn; + int r; + + r = follow_pfn(vma, addr, &pfn); + if (r) { + /* + * get_user_pages fails for VM_IO and VM_PFNMAP vmas and does + * not call the fault handler, so do it here. + */ + bool unlocked = false; + r = fixup_user_fault(current, current->mm, addr, + (write_fault ? FAULT_FLAG_WRITE : 0), + &unlocked); + if (unlocked) + return -EAGAIN; + if (r) + return r; + + r = follow_pfn(vma, addr, &pfn); + if (r) + return r; + + } + + + /* + * Get a reference here because callers of *hva_to_pfn* and + * *gfn_to_pfn* ultimately call kvm_release_pfn_clean on the + * returned pfn. This is only needed if the VMA has VM_MIXEDMAP + * set, but the kvm_get_pfn/kvm_release_pfn_clean pair will + * simply do nothing for reserved pfns. + * + * Whoever called remap_pfn_range is also going to call e.g. + * unmap_mapping_range before the underlying pages are freed, + * causing a call to our MMU notifier. + */ + kvm_get_pfn(pfn); + + *p_pfn = pfn; return 0; } @@ -1493,12 +1529,15 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async, goto exit; } +retry: vma = find_vma_intersection(current->mm, addr, addr + 1); if (vma == NULL) pfn = KVM_PFN_ERR_FAULT; else if (vma->vm_flags & (VM_IO | VM_PFNMAP)) { r = hva_to_pfn_remapped(vma, addr, async, write_fault, &pfn); + if (r == -EAGAIN) + goto retry; if (r < 0) pfn = KVM_PFN_ERR_FAULT; } else { |