Commit add6a0cd authored by Paolo Bonzini's avatar Paolo Bonzini

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: default avatarNeo Jia <cjia@nvidia.com>
Reported-by: default avatarKirti Wankhede <kwankhede@nvidia.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 92176a8e
...@@ -720,6 +720,7 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, ...@@ -720,6 +720,7 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
} }
return 0; return 0;
} }
EXPORT_SYMBOL_GPL(fixup_user_fault);
static __always_inline long __get_user_pages_locked(struct task_struct *tsk, static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
struct mm_struct *mm, struct mm_struct *mm,
......
...@@ -1446,9 +1446,45 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, ...@@ -1446,9 +1446,45 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
unsigned long addr, bool *async, unsigned long addr, bool *async,
bool write_fault, kvm_pfn_t *p_pfn) bool write_fault, kvm_pfn_t *p_pfn)
{ {
*p_pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + unsigned long pfn;
vma->vm_pgoff; int r;
BUG_ON(!kvm_is_reserved_pfn(*p_pfn));
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; return 0;
} }
...@@ -1493,12 +1529,15 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async, ...@@ -1493,12 +1529,15 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
goto exit; goto exit;
} }
retry:
vma = find_vma_intersection(current->mm, addr, addr + 1); vma = find_vma_intersection(current->mm, addr, addr + 1);
if (vma == NULL) if (vma == NULL)
pfn = KVM_PFN_ERR_FAULT; pfn = KVM_PFN_ERR_FAULT;
else if (vma->vm_flags & (VM_IO | VM_PFNMAP)) { else if (vma->vm_flags & (VM_IO | VM_PFNMAP)) {
r = hva_to_pfn_remapped(vma, addr, async, write_fault, &pfn); r = hva_to_pfn_remapped(vma, addr, async, write_fault, &pfn);
if (r == -EAGAIN)
goto retry;
if (r < 0) if (r < 0)
pfn = KVM_PFN_ERR_FAULT; pfn = KVM_PFN_ERR_FAULT;
} else { } else {
......
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