Re: [PATCH 19/19] vfio/pci: Implement huge_fault support

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 14 Aug 2024 10:25:08 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Fri, Aug 09, 2024 at 12:09:09PM -0400, Peter Xu wrote:
> > @@ -1672,30 +1679,49 @@ static vm_fault_t vfio_pci_mmap_fault(struct vm_fault *vmf)
> >  	if (vdev->pm_runtime_engaged || !__vfio_pci_memory_enabled(vdev))
> >  		goto out_unlock;
> >  
> > -	ret = vmf_insert_pfn(vma, vmf->address, pfn + pgoff);
> > -	if (ret & VM_FAULT_ERROR)
> > -		goto out_unlock;
> > -
> > -	/*
> > -	 * Pre-fault the remainder of the vma, abort further insertions and
> > -	 * supress error if fault is encountered during pre-fault.
> > -	 */
> > -	for (; addr < vma->vm_end; addr += PAGE_SIZE, pfn++) {
> > -		if (addr == vmf->address)
> > -			continue;
> > -
> > -		if (vmf_insert_pfn(vma, addr, pfn) & VM_FAULT_ERROR)
> > -			break;
> > +	switch (order) {
> > +	case 0:
> > +		ret = vmf_insert_pfn(vma, vmf->address, pfn + pgoff);
> > +		break;
> > +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP
> > +	case PMD_ORDER:
> > +		ret = vmf_insert_pfn_pmd(vmf, __pfn_to_pfn_t(pfn + pgoff,
> > +							     PFN_DEV), false);
> > +		break;
> > +#endif
> > +#ifdef CONFIG_ARCH_SUPPORTS_PUD_PFNMAP
> > +	case PUD_ORDER:
> > +		ret = vmf_insert_pfn_pud(vmf, __pfn_to_pfn_t(pfn + pgoff,
> > +							     PFN_DEV), false);
> > +		break;
> > +#endif  
> 
> I feel like this switch should be in some general function? 
> 
> vmf_insert_pfn_order(vmf, order, __pfn_to_pfn_t(pfn + pgoff, PFN_DEV), false);
> 
> No reason to expose every driver to this when you've already got a
> nice contract to have the driver work on the passed in order.
> 
> What happens if the driver can't get a PFN that matches the requested
> order?

There was some alignment and size checking chopped from the previous
reply that triggered a fallback, but in general PCI BARs are a power of
two and naturally aligned, so there should always be an order aligned
pfn.  Thanks,

Alex