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Message-ID: <6feb6f37-dfb9-0fe1-1303-2744ad2758d9@suse.cz>
Date: Mon, 9 Oct 2023 17:22:33 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>
Cc: "=Liam R . Howlett" <Liam.Howlett@...cle.com>,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/4] mm: abstract the vma_merge()/split_vma() pattern for
mprotect() et al.
On 10/8/23 22:23, Lorenzo Stoakes wrote:
> mprotect() and other functions which change VMA parameters over a range
> each employ a pattern of:-
>
> 1. Attempt to merge the range with adjacent VMAs.
> 2. If this fails, and the range spans a subset of the VMA, split it
> accordingly.
>
> This is open-coded and duplicated in each case. Also in each case most of
> the parameters passed to vma_merge() remain the same.
>
> Create a new static function, vma_modify(), which abstracts this operation,
> accepting only those parameters which can be changed.
>
> To avoid the mess of invoking each function call with unnecessary
> parameters, create wrapper functions for each of the modify operations,
> parameterised only by what is required to perform the action.
Nice!
> Note that the userfaultfd_release() case works even though it does not
> split VMAs - since start is set to vma->vm_start and end is set to
> vma->vm_end, the split logic does not trigger.
>
> In addition, since we calculate pgoff to be equal to vma->vm_pgoff + (start
> - vma->vm_start) >> PAGE_SHIFT, and start - vma->vm_start will be 0 in this
> instance, this invocation will remain unchanged.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
> ---
> fs/userfaultfd.c | 53 +++++++++-----------------
> include/linux/mm.h | 23 ++++++++++++
> mm/madvise.c | 25 ++++---------
> mm/mempolicy.c | 20 ++--------
> mm/mlock.c | 24 ++++--------
> mm/mmap.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++
> mm/mprotect.c | 27 ++++----------
> 7 files changed, 157 insertions(+), 108 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index a7c6ef764e63..9e5232d23927 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -927,11 +927,10 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
> continue;
> }
> new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
> - prev = vma_merge(&vmi, mm, prev, vma->vm_start, vma->vm_end,
> - new_flags, vma->anon_vma,
> - vma->vm_file, vma->vm_pgoff,
> - vma_policy(vma),
> - NULL_VM_UFFD_CTX, anon_vma_name(vma));
> + prev = vma_modify_uffd(&vmi, prev, vma, vma->vm_start,
> + vma->vm_end, new_flags,
> + NULL_VM_UFFD_CTX);
> +
> if (prev) {
> vma = prev;
> } else {
> @@ -1331,7 +1330,6 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> unsigned long start, end, vma_end;
> struct vma_iterator vmi;
> bool wp_async = userfaultfd_wp_async_ctx(ctx);
> - pgoff_t pgoff;
>
> user_uffdio_register = (struct uffdio_register __user *) arg;
>
> @@ -1484,26 +1482,18 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> vma_end = min(end, vma->vm_end);
>
> new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
> - pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
> - prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags,
> - vma->anon_vma, vma->vm_file, pgoff,
> - vma_policy(vma),
> - ((struct vm_userfaultfd_ctx){ ctx }),
> - anon_vma_name(vma));
> + prev = vma_modify_uffd(&vmi, prev, vma, start, vma_end,
> + new_flags,
> + ((struct vm_userfaultfd_ctx){ ctx }));
> if (prev) {
This will hit also for IS_ERR(prev), no?
> /* vma_merge() invalidated the mas */
> vma = prev;
> goto next;
> }
> - if (vma->vm_start < start) {
> - ret = split_vma(&vmi, vma, start, 1);
> - if (ret)
> - break;
> - }
> - if (vma->vm_end > end) {
> - ret = split_vma(&vmi, vma, end, 0);
> - if (ret)
> - break;
> +
> + if (IS_ERR(prev)) {
So here's too late to test for it. AFAICS the other usages are like this as
well.
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a7b667786cde..c069813f215f 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3253,6 +3253,29 @@ extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
> unsigned long addr, unsigned long len, pgoff_t pgoff,
> bool *need_rmap_locks);
> extern void exit_mmap(struct mm_struct *);
> +struct vm_area_struct *vma_modify_flags(struct vma_iterator *vmi,
> + struct vm_area_struct *prev,
> + struct vm_area_struct *vma,
> + unsigned long start, unsigned long end,
> + unsigned long new_flags);
> +struct vm_area_struct *vma_modify_flags_name(struct vma_iterator *vmi,
> + struct vm_area_struct *prev,
> + struct vm_area_struct *vma,
> + unsigned long start,
> + unsigned long end,
> + unsigned long new_flags,
> + struct anon_vma_name *new_name);
> +struct vm_area_struct *vma_modify_policy(struct vma_iterator *vmi,
> + struct vm_area_struct *prev,
> + struct vm_area_struct *vma,
> + unsigned long start, unsigned long end,
> + struct mempolicy *new_pol);
> +struct vm_area_struct *vma_modify_uffd(struct vma_iterator *vmi,
> + struct vm_area_struct *prev,
> + struct vm_area_struct *vma,
> + unsigned long start, unsigned long end,
> + unsigned long new_flags,
> + struct vm_userfaultfd_ctx new_ctx);
Could these be instead static inline wrappers, and vma_modify exported
instead of static?
Maybe we could also move this to mm/internal.h? Which would mean
fs/userfaultfd.c would have to start including it, but as it's already so
much rooted in mm, it shouldn't be wrong?
>
> static inline int check_data_rlimit(unsigned long rlim,
> unsigned long new,
> diff --git a/mm/madvise.c b/mm/madvise.c
> index a4a20de50494..73024693d5c8 100644
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