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

[Chris Wilson]

On Thu, Jun 19, 2014 at 03:57:46PM +0300, Kirill A. Shutemov wrote:
> 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.

That I agree with.
 
> 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.

Looked at just returning the address remap_pfn_range() got up to, which is
easy enough, but I think given that remap_pfn_range() will clean up
correctly after a failed remap, any EBUSY from partway through would be
a pathological driver error. 
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre