Re: [PATCH 5/5] vfio-pci: Best-effort huge pfnmaps with !MAP_FIXED mappings

[Peter Xu]

On Fri, Jun 13, 2025 at 10:44:42AM -0700, Alex Mastro wrote:
> Thank you Peter!
> 
> I packported this series to our 6.13.2 tree and validated that it does indeed
> provide equivalent, optimal faulting to our manual alignment approach when we
> mmap with !MAP_FIXED. This addresses the issue we discovered in [1].
> 
> The test case is performing mmap with offset=0x40006000000, size=0xdf9e00000,
> and we see that the head and tail (975) are faulted at 2M, and middle (54) at
> 1G. The vma returned by mmap looks nice: 0x7f8646000000.
> 
> $ sudo bpftrace -q -e 'fexit:vfio_pci_mmap_huge_fault { printf("order=%d, ret=0x%x\n", args.order, retval); }' 2>&1 > ~/dump
> $ cat ~/dump | sort | uniq -c | sort -nr
>     975 order=9, ret=0x100
>      54 order=18, ret=0x100
>       2 order=18, ret=0x800
> 
> [1] https://lore.kernel.org/linux-pci/20250529214414.1508155-1-amastro@xxxxxx/
> 
> Tested-by: Alex Mastro <amastro@xxxxxx>

Great to know it works as expected, thanks for the quick feedback!

-- 
Peter Xu