RE: [PATCH V1 0/5] memfd-pin huge page fixes

["Kasireddy, Vivek" <vivek.kasireddy@intel.com>]

> Subject: Re: [PATCH V1 0/5] memfd-pin huge page fixes
> 
> On 9/3/2024 9:12 PM, Kasireddy, Vivek wrote:
> > Hi Steve,
> >
> >> Subject: [PATCH V1 0/5] memfd-pin huge page fixes
> >>
> >> Fix multiple bugs that occur when using memfd_pin_folios with hugetlb
> >> pages
> >> and THP.  The hugetlb bugs only bite when the page is not yet faulted in
> >> when memfd_pin_folios is called.  The THP bug bites when the starting
> offset
> >> passed to memfd_pin_folios is not huge page aligned.  See the commit
> >> messages
> >> for details.
> > Thank you for fixing these bugs. I have Acked all patches except for patch
> #1,
> > as my understanding of xarrays is limited at this point.
> >
> > Also, could you please briefly describe how you have exercised
> memfd_alloc_folio()
> > code path or what tests you have run to uncover these bugs? I'd like to
> > figure out ways to augment the list of udmabuf tests to validate scenarios
> > where hugetlb pages are not faulted in and memfd_pin_folios() is called.
> 
> I am extending iommufd to support memfd pinning, so I added a new ioctl
> which
> takes an fd, offset, and length to pin.  I am just getting started, so currently
> it does nothing more than call memfd_pin_folios immediately followed by
> unpin_folios.
> Then exit the process.  That is sufficient to trigger all the bugs except the alloc
> race panic. I tested with these files:
>    /dev/hugepages/file
>    /dev/shm/file    with: mount -o remount,huge=always /dev/shm
>    memfd_create(MFD_HUGETLB)
>    memfd_create(0)  with: echo always >
> /sys/kernel/mm/transparent_hugepage/shmem_enabled
Thank you for explaining your test-case.

Thanks,
Vivek

> 
> - Steve
> 
> >> Steve Sistare (5):
> >>    mm/filemap: fix filemap_get_folios_contig THP panic
> >>    mm/hugetlb: fix memfd_pin_folios free_huge_pages leak
> >>    mm/hugetlb: fix memfd_pin_folios resv_huge_pages leak
> >>    mm/gup: fix memfd_pin_folios hugetlb page allocation
> >>    mm/gup: fix memfd_pin_folios alloc race panic
> >>
> >>   include/linux/hugetlb.h | 10 ++++++++++
> >>   mm/filemap.c            |  4 ++++
> >>   mm/gup.c                |  5 ++++-
> >>   mm/hugetlb.c            | 17 +++++++++++++++++
> >>   mm/memfd.c              | 15 +++++++++------
> >>   5 files changed, 44 insertions(+), 7 deletions(-)
> >>
> >> --
> >> 1.8.3.1
> >