[Intel-gfx] [PATCH] mm: Report attempts to overwrite PTE from remap_pfn_range()

[Kirill A. Shutemov]

Chris Wilson wrote:
> On Thu, Jun 19, 2014 at 02:50:18PM +0300, Kirill A. Shutemov wrote:
> > > +	if (err) {
> > >  		untrack_pfn(vma, pfn, PAGE_ALIGN(size));
> > > +		if (err != -EBUSY)
> > > +			zap_page_range_single(vma, addr, size, NULL);
> > 
> > Hm. If I read it correctly, you zap whole range, not only what you've
> > set up. Looks wrong.
> 
> Yes. I didn't fancy threading the last touched pte back, but that should
> be easier if moving to a struct.
>  
> > And for after zap, you probably whant to return -EBUSY to caller of
> > remap_pfn_range(), not -EINVAL.
> 
> No, it has to be EINVAL for my purpose. If we return EBUSY, the caller
> will just report VM_NOPAGE back to the fault handler, and the fault will
> be retriggered - but the overlapping object will still be present.

IIUC, what you're saying makes sense only if the range starts from PTE
you've got fault to. I failed to see why this assumption should be part of
remap_pfn_range() interface.

One possible option is to create a variant of remap_pfn_range() which will
return how many PTEs it was able to setup, before hitting the !pte_none().
Caller will decide what to do with partially filled range.

-- 
 Kirill A. Shutemov