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Message-ID: <CAJHvVcjjX8FEsdngUTH+0c3C17T0ud-FXj=GJf90R8hn8PKekA@mail.gmail.com>
Date: Tue, 9 Mar 2021 11:57:26 -0800
From: Axel Rasmussen <axelrasmussen@...gle.com>
To: Zi Yan <ziy@...dia.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
Jerome Glisse <jglisse@...hat.com>,
Joe Perches <joe@...ches.com>,
Lokesh Gidra <lokeshgidra@...gle.com>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
Peter Xu <peterx@...hat.com>, Shaohua Li <shli@...com>,
Shuah Khan <shuah@...nel.org>, Wang Qing <wangqing@...o.com>,
LKML <linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
linux-kselftest@...r.kernel.org, Brian Geffon <bgeffon@...gle.com>,
Cannon Matthews <cannonmatthews@...gle.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Michel Lespinasse <walken@...gle.com>,
Mina Almasry <almasrymina@...gle.com>,
Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v2 1/5] userfaultfd: support minor fault handling for shmem
On Tue, Mar 9, 2021 at 11:52 AM Zi Yan <ziy@...dia.com> wrote:
>
> On 1 Mar 2021, at 19:01, Axel Rasmussen wrote:
>
> > Modify the userfaultfd register API to allow registering shmem VMAs in
> > minor mode. Modify the shmem mcopy implementation to support
> > UFFDIO_CONTINUE in order to resolve such faults.
> >
> > Combine the shmem mcopy handler functions into a single
> > shmem_mcopy_atomic_pte, which takes a mode parameter. This matches how
> > the hugetlbfs implementation is structured, and lets us remove a good
> > chunk of boilerplate.
> >
> > Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> > ---
> > fs/userfaultfd.c | 6 +--
> > include/linux/shmem_fs.h | 26 ++++-----
> > include/uapi/linux/userfaultfd.h | 4 +-
> > mm/memory.c | 8 +--
> > mm/shmem.c | 92 +++++++++++++++-----------------
> > mm/userfaultfd.c | 27 +++++-----
> > 6 files changed, 79 insertions(+), 84 deletions(-)
> >
> > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > index 14f92285d04f..9f3b8684cf3c 100644
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -1267,8 +1267,7 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
> > }
> >
> > if (vm_flags & VM_UFFD_MINOR) {
> > - /* FIXME: Add minor fault interception for shmem. */
> > - if (!is_vm_hugetlb_page(vma))
> > + if (!(is_vm_hugetlb_page(vma) || vma_is_shmem(vma)))
> > return false;
> > }
> >
> > @@ -1941,7 +1940,8 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
> > /* report all available features and ioctls to userland */
> > uffdio_api.features = UFFD_API_FEATURES;
> > #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
> > - uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS;
> > + uffdio_api.features &=
> > + ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
> > #endif
> > uffdio_api.ioctls = UFFD_API_IOCTLS;
> > ret = -EFAULT;
> > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> > index d82b6f396588..f0919c3722e7 100644
> > --- a/include/linux/shmem_fs.h
> > +++ b/include/linux/shmem_fs.h
> > @@ -9,6 +9,7 @@
> > #include <linux/percpu_counter.h>
> > #include <linux/xattr.h>
> > #include <linux/fs_parser.h>
> > +#include <linux/userfaultfd_k.h>
> >
> > /* inode in-kernel data */
> >
> > @@ -122,21 +123,16 @@ static inline bool shmem_file(struct file *file)
> > extern bool shmem_charge(struct inode *inode, long pages);
> > extern void shmem_uncharge(struct inode *inode, long pages);
> >
> > +#ifdef CONFIG_USERFAULTFD
> > #ifdef CONFIG_SHMEM
> > -extern int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
> > - struct vm_area_struct *dst_vma,
> > - unsigned long dst_addr,
> > - unsigned long src_addr,
> > - struct page **pagep);
> > -extern int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
> > - pmd_t *dst_pmd,
> > - struct vm_area_struct *dst_vma,
> > - unsigned long dst_addr);
> > -#else
> > -#define shmem_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma, dst_addr, \
> > - src_addr, pagep) ({ BUG(); 0; })
> > -#define shmem_mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma, \
> > - dst_addr) ({ BUG(); 0; })
> > -#endif
> > +int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
> > + struct vm_area_struct *dst_vma,
> > + unsigned long dst_addr, unsigned long src_addr,
> > + enum mcopy_atomic_mode mode, struct page **pagep);
> > +#else /* !CONFIG_SHMEM */
> > +#define shmem_mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, \
> > + src_addr, mode, pagep) ({ BUG(); 0; })
> > +#endif /* CONFIG_SHMEM */
> > +#endif /* CONFIG_USERFAULTFD */
> >
> > #endif
> > diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
> > index bafbeb1a2624..47d9790d863d 100644
> > --- a/include/uapi/linux/userfaultfd.h
> > +++ b/include/uapi/linux/userfaultfd.h
> > @@ -31,7 +31,8 @@
> > UFFD_FEATURE_MISSING_SHMEM | \
> > UFFD_FEATURE_SIGBUS | \
> > UFFD_FEATURE_THREAD_ID | \
> > - UFFD_FEATURE_MINOR_HUGETLBFS)
> > + UFFD_FEATURE_MINOR_HUGETLBFS | \
> > + UFFD_FEATURE_MINOR_SHMEM)
> > #define UFFD_API_IOCTLS \
> > ((__u64)1 << _UFFDIO_REGISTER | \
> > (__u64)1 << _UFFDIO_UNREGISTER | \
> > @@ -196,6 +197,7 @@ struct uffdio_api {
> > #define UFFD_FEATURE_SIGBUS (1<<7)
> > #define UFFD_FEATURE_THREAD_ID (1<<8)
> > #define UFFD_FEATURE_MINOR_HUGETLBFS (1<<9)
> > +#define UFFD_FEATURE_MINOR_SHMEM (1<<10)
> > __u64 features;
> >
> > __u64 ioctls;
> > diff --git a/mm/memory.c b/mm/memory.c
> > index c8e357627318..a1e5ff55027e 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -3929,9 +3929,11 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
> > * something).
> > */
> > if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
> > - ret = do_fault_around(vmf);
> > - if (ret)
> > - return ret;
> > + if (likely(!userfaultfd_minor(vmf->vma))) {
> > + ret = do_fault_around(vmf);
> > + if (ret)
> > + return ret;
> > + }
> > }
> >
> > ret = __do_fault(vmf);
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index b2db4ed0fbc7..6f81259fabb3 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -77,7 +77,6 @@ static struct vfsmount *shm_mnt;
> > #include <linux/syscalls.h>
> > #include <linux/fcntl.h>
> > #include <uapi/linux/memfd.h>
> > -#include <linux/userfaultfd_k.h>
> > #include <linux/rmap.h>
> > #include <linux/uuid.h>
> >
> > @@ -1785,8 +1784,8 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index,
> > * vm. If we swap it in we mark it dirty since we also free the swap
> > * entry since a page cannot live in both the swap and page cache.
> > *
> > - * vmf and fault_type are only supplied by shmem_fault:
> > - * otherwise they are NULL.
> > + * vma, vmf, and fault_type are only supplied by shmem_fault: otherwise they
> > + * are NULL.
> > */
> > static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
> > struct page **pagep, enum sgp_type sgp, gfp_t gfp,
> > @@ -1830,6 +1829,12 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
> > return error;
> > }
> >
> > + if (page && vma && userfaultfd_minor(vma)) {
> > + unlock_page(page);
> > + *fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
> > + return 0;
> > + }
> > +
> > if (page)
> > hindex = page->index;
> > if (page && sgp == SGP_WRITE)
> > @@ -2354,14 +2359,12 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
> > return inode;
> > }
> >
> > -static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
> > - pmd_t *dst_pmd,
> > - struct vm_area_struct *dst_vma,
> > - unsigned long dst_addr,
> > - unsigned long src_addr,
> > - bool zeropage,
> > - struct page **pagep)
> > +int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
> > + struct vm_area_struct *dst_vma,
> > + unsigned long dst_addr, unsigned long src_addr,
> > + enum mcopy_atomic_mode mode, struct page **pagep)
> > {
> > + bool is_continue = (mode == MCOPY_ATOMIC_CONTINUE);
> > struct inode *inode = file_inode(dst_vma->vm_file);
> > struct shmem_inode_info *info = SHMEM_I(inode);
> > struct address_space *mapping = inode->i_mapping;
> > @@ -2378,12 +2381,17 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
> > if (!shmem_inode_acct_block(inode, 1))
> > goto out;
> >
> > - if (!*pagep) {
> > + if (is_continue) {
> > + ret = -EFAULT;
> > + page = find_lock_page(mapping, pgoff);
> > + if (!page)
> > + goto out_unacct_blocks;
> > + } else if (!*pagep) {
> > page = shmem_alloc_page(gfp, info, pgoff);
> > if (!page)
> > goto out_unacct_blocks;
> >
> > - if (!zeropage) { /* mcopy_atomic */
> > + if (mode == MCOPY_ATOMIC_NORMAL) { /* mcopy_atomic */
> > page_kaddr = kmap_atomic(page);
> > ret = copy_from_user(page_kaddr,
> > (const void __user *)src_addr,
>
> Hi Axel,
>
> shmem_mcopy_atomic_pte is not guarded by CONFIG_USERFAULTFD, thus it is
> causing compilation errors due to the use of enum mcopy_atomic_mode mode,
> when CONFIG_USERFAULTFD is not set.
Ah, my apologies, I guarded it in the header but forgot to do so in
shmem.c. I'll send an updated patch today.
>
>
> —
> Best Regards,
> Yan Zi
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