Re: R/W HG memory mappings with kvm?

[Avi Kivity <avi@redhat.com>]

On 08/24/2009 07:55 AM, Avi Kivity wrote:
> On 08/24/2009 12:59 AM, Stephen Donnelly wrote:
>> On Thu, Aug 20, 2009 at 12:14 AM, Avi Kivity<avi@redhat.com>  wrote:
>>> On 08/13/2009 07:07 AM, Stephen Donnelly wrote:
>>>> npages = get_user_pages_fast(addr, 1, 1, page); returns -EFAULT,
>>>> presumably because (vma->vm_flags&    (VM_IO | VM_PFNMAP)).
>>>>
>>>> It takes then unlikely branch, and checks the vma, but I don't
>>>> understand what it is doing here: pfn = ((addr - vma->vm_start)>>
>>>> PAGE_SHIFT) + vma->vm_pgoff;
>>> It's calculating the pfn according to pfnmap rules.
>>  From what I understand this will only work when remapping 'main
>> memory', e.g. where the pgoff is equal to the physical page offset?
>> VMAs that remap IO memory will usually set pgoff to 0 for the start of
>> the mapping.
>
> If so, how do they calculate the pfn when mapping pages?  kvm needs to 
> be able to do the same thing.

Maybe the simplest thing is to call vma->vm_ops->fault here.  
Marcelo/Chris?  Context is improving gfn_to_pfn() on the mmio path.

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