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From:   Brian Geffon <bgeffon@google.com>
Date:   Thu, 22 Jul 2021 12:00:36 -0400
Message-ID: <CADyq12xr=99yNHMmAKik+0BHJz1cc_YKL0XNpe=cA1ddkoBFSg@mail.gmail.com>
Subject: Re: [PATCH v2] mm/mremap: Don't account pages in vma_to_resize()
To:     Dmitry Safonov <dima@arista.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Chen Wandun <chenwandun@huawei.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@redhat.com>, Jason Gunthorpe <jgg@ziepe.ca>,
        John Hubbard <jhubbard@nvidia.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Minchan Kim <minchan@kernel.org>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Russell King <linux@armlinux.org.uk>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Wei Yongjun <weiyongjun1@huawei.com>,
        Will Deacon <will@kernel.org>
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Whoops I missed that you did remove it from vma_to_resize() so then it
looks good to me.

Acked-By: Brian Geffon <bgeffon@google.com>

On Thu, Jul 22, 2021 at 11:58 AM Brian Geffon <bgeffon@google.com> wrote:
>
> On Wed, Jul 21, 2021 at 9:13 AM Dmitry Safonov <dima@arista.com> wrote:
> >
> > All this vm_unacct_memory(charged) dance seems to complicate the life
> > without a good reason. Furthermore, it seems not always done right on
> > error-pathes in mremap_to().
> > And worse than that: this `charged' difference is sometimes
> > double-accounted for growing MREMAP_DONTUNMAP mremap()s in move_vma():
> > : if (security_vm_enough_memory_mm(mm, new_len >> PAGE_SHIFT))
> >
> > Let's not do this.
> > Account memory in mremap() fast-path for growing VMAs or in move_vma()
> > for actually moving things. The same simpler way as it's done by
> > vm_stat_account(), but with a difference to call
> > security_vm_enough_memory_mm() before copying/adjusting VMA.
> >
> > Originally noticed by Chen Wandun:
> > https://lkml.kernel.org/r/20210717101942.120607-1-chenwandun@huawei.com
> >
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Andy Lutomirski <luto@kernel.org>
> > Cc: Brian Geffon <bgeffon@google.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Chen Wandun <chenwandun@huawei.com>
> > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Dave Jiang <dave.jiang@intel.com>
> > Cc: Hugh Dickins <hughd@google.com>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
> > Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > Cc: Minchan Kim <minchan@kernel.org>
> > Cc: Ralph Campbell <rcampbell@nvidia.com>
> > Cc: Russell King <linux@armlinux.org.uk>
> > Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Vishal Verma <vishal.l.verma@intel.com>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Wei Yongjun <weiyongjun1@huawei.com>
> > Cc: Will Deacon <will@kernel.org>
> > Fixes: e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
> > Signed-off-by: Dmitry Safonov <dima@arista.com>
> > ---
> >  mm/mremap.c | 50 ++++++++++++++++++++++----------------------------
> >  1 file changed, 22 insertions(+), 28 deletions(-)
> >
> > diff --git a/mm/mremap.c b/mm/mremap.c
> > index 5989d3990020..b90c8e732e29 100644
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -565,6 +565,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >                 bool *locked, unsigned long flags,
> >                 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
> >  {
> > +       long to_account = new_len - old_len;
> >         struct mm_struct *mm = vma->vm_mm;
> >         struct vm_area_struct *new_vma;
> >         unsigned long vm_flags = vma->vm_flags;
> > @@ -583,6 +584,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >         if (mm->map_count >= sysctl_max_map_count - 3)
> >                 return -ENOMEM;
> >
> > +       if (unlikely(flags & MREMAP_DONTUNMAP))
> > +               to_account = new_len;
> > +
> >         if (vma->vm_ops && vma->vm_ops->may_split) {
> >                 if (vma->vm_start != old_addr)
> >                         err = vma->vm_ops->may_split(vma, old_addr);
> > @@ -604,8 +608,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >         if (err)
> >                 return err;
> >
> > -       if (unlikely(flags & MREMAP_DONTUNMAP && vm_flags & VM_ACCOUNT)) {
> > -               if (security_vm_enough_memory_mm(mm, new_len >> PAGE_SHIFT))
> > +       if (vm_flags & VM_ACCOUNT) {
> > +               if (security_vm_enough_memory_mm(mm, to_account >> PAGE_SHIFT))
> >                         return -ENOMEM;
> >         }
> >
> > @@ -613,8 +617,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
> >                            &need_rmap_locks);
> >         if (!new_vma) {
> > -               if (unlikely(flags & MREMAP_DONTUNMAP && vm_flags & VM_ACCOUNT))
> > -                       vm_unacct_memory(new_len >> PAGE_SHIFT);
> > +               if (vm_flags & VM_ACCOUNT)
> > +                       vm_unacct_memory(to_account >> PAGE_SHIFT);
> >                 return -ENOMEM;
> >         }
> >
> > @@ -708,8 +712,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >  }
> >
> >  static struct vm_area_struct *vma_to_resize(unsigned long addr,
> > -       unsigned long old_len, unsigned long new_len, unsigned long flags,
> > -       unsigned long *p)
> > +       unsigned long old_len, unsigned long new_len, unsigned long flags)
> >  {
> >         struct mm_struct *mm = current->mm;
> >         struct vm_area_struct *vma;
> > @@ -768,13 +771,6 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> >                                 (new_len - old_len) >> PAGE_SHIFT))
> >                 return ERR_PTR(-ENOMEM);
> >
> > -       if (vma->vm_flags & VM_ACCOUNT) {
> > -               unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
> > -               if (security_vm_enough_memory_mm(mm, charged))
> > -                       return ERR_PTR(-ENOMEM);
> > -               *p = charged;
> > -       }
> > -
> >         return vma;
> >  }
> >
> > @@ -787,7 +783,6 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> >         struct mm_struct *mm = current->mm;
> >         struct vm_area_struct *vma;
> >         unsigned long ret = -EINVAL;
> > -       unsigned long charged = 0;
> >         unsigned long map_flags = 0;
> >
> >         if (offset_in_page(new_addr))
> > @@ -830,7 +825,7 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> >                 old_len = new_len;
> >         }
> >
> > -       vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
> > +       vma = vma_to_resize(addr, old_len, new_len, flags);
> >         if (IS_ERR(vma)) {
> >                 ret = PTR_ERR(vma);
> >                 goto out;
> > @@ -853,7 +848,7 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> >                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
> >                                 map_flags);
> >         if (IS_ERR_VALUE(ret))
> > -               goto out1;
> > +               goto out;
> >
> >         /* We got a new mapping */
> >         if (!(flags & MREMAP_FIXED))
> > @@ -862,12 +857,6 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> >         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
> >                        uf_unmap);
> >
> > -       if (!(offset_in_page(ret)))
> > -               goto out;
> > -
> > -out1:
> > -       vm_unacct_memory(charged);
> > -
> >  out:
> >         return ret;
> >  }
> > @@ -899,7 +888,6 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> >         struct mm_struct *mm = current->mm;
> >         struct vm_area_struct *vma;
> >         unsigned long ret = -EINVAL;
> > -       unsigned long charged = 0;
> >         bool locked = false;
> >         bool downgraded = false;
> >         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
> > @@ -981,7 +969,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> >         /*
> >          * Ok, we need to grow..
> >          */
> > -       vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
> > +       vma = vma_to_resize(addr, old_len, new_len, flags);
> >         if (IS_ERR(vma)) {
> >                 ret = PTR_ERR(vma);
> >                 goto out;
> > @@ -992,10 +980,18 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> >         if (old_len == vma->vm_end - addr) {
> >                 /* can we just expand the current mapping? */
> >                 if (vma_expandable(vma, new_len - old_len)) {
> > -                       int pages = (new_len - old_len) >> PAGE_SHIFT;
> > +                       long pages = (new_len - old_len) >> PAGE_SHIFT;
> > +
> > +                       if (vma->vm_flags & VM_ACCOUNT) {
> > +                               if (security_vm_enough_memory_mm(mm, pages)) {
> > +                                       ret = -ENOMEM;
> > +                                       goto out;
> > +                               }
> > +                       }
>
> Wasn't this whole check already performed in vma_to_resize()?
>
> >
> >                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
> >                                        vma->vm_pgoff, NULL)) {
> > +                               vm_unacct_memory(pages);
> >                                 ret = -ENOMEM;
> >                                 goto out;
> >                         }
> > @@ -1034,10 +1030,8 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> >                                &locked, flags, &uf, &uf_unmap);
> >         }
> >  out:
> > -       if (offset_in_page(ret)) {
> > -               vm_unacct_memory(charged);
> > +       if (offset_in_page(ret))
> >                 locked = false;
> > -       }
> >         if (downgraded)
> >                 mmap_read_unlock(current->mm);
> >         else
> > --
> > 2.32.0
> >