From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: akpm@linux-foundation.org, dan.j.williams@intel.com,
mhocko@suse.com, keith.busch@intel.com,
kirill.shutemov@linux.intel.com,
alexander.h.duyck@linux.intel.com, ira.weiny@intel.com,
andreyknvl@google.com, arunks@codeaurora.org, vbabka@suse.cz,
cl@linux.com, riel@surriel.com, keescook@chromium.org,
hannes@cmpxchg.org, npiggin@gmail.com,
mathieu.desnoyers@efficios.com, shakeelb@google.com, guro@fb.com,
aarcange@redhat.com, hughd@google.com, jglisse@redhat.com,
mgorman@techsingularity.net, daniel.m.jordan@oracle.com,
jannh@google.com, kilobyte@angband.pl, linux-api@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 2/7] mm: Extend copy_vma()
Date: Tue, 21 May 2019 11:48:26 +0300 [thread overview]
Message-ID: <d4664163-35e2-10e0-9c7b-44fa090b7198@virtuozzo.com> (raw)
In-Reply-To: <20190521081821.fbngbxk7lzwrb7md@box>
Hi, Kirill,
On 21.05.2019 11:18, Kirill A. Shutemov wrote:
> On Mon, May 20, 2019 at 05:00:12PM +0300, Kirill Tkhai wrote:
>> This prepares the function to copy a vma between
>> two processes. Two new arguments are introduced.
>
> This kind of changes requires a lot more explanation in commit message,
> describing all possible corner cases> For instance, I would really like to see a story on why logic around
> need_rmap_locks is safe after the change.
Let me fast answer on the below question firstly, and later I'll write
wide explanations, since this requires much more time.
>>
>> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
>> ---
>> include/linux/mm.h | 4 ++--
>> mm/mmap.c | 33 ++++++++++++++++++++++++---------
>> mm/mremap.c | 4 ++--
>> 3 files changed, 28 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 0e8834ac32b7..afe07e4a76f8 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2329,8 +2329,8 @@ extern void __vma_link_rb(struct mm_struct *, struct vm_area_struct *,
>> struct rb_node **, struct rb_node *);
>> extern void unlink_file_vma(struct vm_area_struct *);
>> extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
>> - unsigned long addr, unsigned long len, pgoff_t pgoff,
>> - bool *need_rmap_locks);
>> + struct mm_struct *, unsigned long addr, unsigned long len,
>> + pgoff_t pgoff, bool *need_rmap_locks, bool clear_flags_ctx);
>> extern void exit_mmap(struct mm_struct *);
>>
>> static inline int check_data_rlimit(unsigned long rlim,
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index 57803a0a3a5c..99778e724ad1 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -3195,19 +3195,21 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
>> }
>>
>> /*
>> - * Copy the vma structure to a new location in the same mm,
>> - * prior to moving page table entries, to effect an mremap move.
>> + * Copy the vma structure to new location in the same vma
>> + * prior to moving page table entries, to effect an mremap move;
>> */
>> struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>> - unsigned long addr, unsigned long len, pgoff_t pgoff,
>> - bool *need_rmap_locks)
>> + struct mm_struct *mm, unsigned long addr,
>> + unsigned long len, pgoff_t pgoff,
>> + bool *need_rmap_locks, bool clear_flags_ctx)
>> {
>> struct vm_area_struct *vma = *vmap;
>> unsigned long vma_start = vma->vm_start;
>> - struct mm_struct *mm = vma->vm_mm;
>> + struct vm_userfaultfd_ctx uctx;
>> struct vm_area_struct *new_vma, *prev;
>> struct rb_node **rb_link, *rb_parent;
>> bool faulted_in_anon_vma = true;
>> + unsigned long flags;
>>
>> /*
>> * If anonymous vma has not yet been faulted, update new pgoff
>> @@ -3220,15 +3222,25 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>>
>> if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
>> return NULL; /* should never get here */
>> - new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
>> - vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
>> - vma->vm_userfaultfd_ctx);
>> +
>> + uctx = vma->vm_userfaultfd_ctx;
>> + flags = vma->vm_flags;
>> + if (clear_flags_ctx) {
>> + uctx = NULL_VM_UFFD_CTX;
>> + flags &= ~(VM_UFFD_MISSING | VM_UFFD_WP | VM_MERGEABLE |
>> + VM_LOCKED | VM_LOCKONFAULT | VM_WIPEONFORK |
>> + VM_DONTCOPY);
>> + }
>
> Why is the new logic required? No justification given.
Ditto.
>> +
>> + new_vma = vma_merge(mm, prev, addr, addr + len, flags, vma->anon_vma,
>> + vma->vm_file, pgoff, vma_policy(vma), uctx);
>> if (new_vma) {
>> /*
>> * Source vma may have been merged into new_vma
>> */
>> if (unlikely(vma_start >= new_vma->vm_start &&
>> - vma_start < new_vma->vm_end)) {
>> + vma_start < new_vma->vm_end) &&
>> + vma->vm_mm == mm) {
>
> How can vma_merge() succeed if vma->vm_mm != mm?
We don't use vma as an argument of vma_merge(). We use vma as a source of
vma->anon_vma, vma->vm_file and vma_policy().
We search some new_vma in mm with the same characteristics as vma has in vma->vm_mm.
In case of success vma_merge() returns it for us. For example, it may success, when
vma->vm_mm is mm_struct of forked process, while mm is mm_struct of its parent.
[...]
Kirill
next prev parent reply other threads:[~2019-05-21 8:48 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 14:00 [PATCH v2 0/7] mm: process_vm_mmap() -- syscall for duplication a process mapping Kirill Tkhai
2019-05-20 14:00 ` [PATCH v2 1/7] mm: Add process_vm_mmap() syscall declaration Kirill Tkhai
2019-05-21 0:28 ` Ira Weiny
2019-05-21 8:29 ` Kirill Tkhai
2019-05-20 14:00 ` [PATCH v2 2/7] mm: Extend copy_vma() Kirill Tkhai
2019-05-21 8:18 ` Kirill A. Shutemov
2019-05-21 8:48 ` Kirill Tkhai [this message]
2019-05-20 14:00 ` [PATCH v2 3/7] mm: Extend copy_page_range() Kirill Tkhai
2019-05-20 14:00 ` [PATCH v2 4/7] mm: Export round_hint_to_min() Kirill Tkhai
2019-05-20 14:00 ` [PATCH v2 5/7] mm: Introduce may_mmap_overlapped_region() helper Kirill Tkhai
2019-05-20 14:00 ` [PATCH v2 6/7] mm: Introduce find_vma_filter_flags() helper Kirill Tkhai
2019-05-20 14:00 ` [PATCH v2 7/7] mm: Add process_vm_mmap() Kirill Tkhai
2019-05-21 14:43 ` [PATCH v2 0/7] mm: process_vm_mmap() -- syscall for duplication a process mapping Andy Lutomirski
2019-05-21 15:52 ` Kirill Tkhai
2019-05-21 15:59 ` Kirill Tkhai
2019-05-21 16:20 ` Jann Horn
2019-05-21 17:03 ` Kirill Tkhai
2019-05-21 17:28 ` Jann Horn
2019-05-22 10:03 ` Kirill Tkhai
2019-05-21 16:43 ` Andy Lutomirski
2019-05-21 17:44 ` Kirill Tkhai
2019-05-23 16:19 ` Andy Lutomirski
2019-05-24 10:36 ` Kirill Tkhai
2019-05-22 15:22 ` Kirill A. Shutemov
2019-05-23 16:11 ` Kirill Tkhai
2019-05-24 10:45 ` Kirill Tkhai
2019-05-24 11:52 ` Kirill A. Shutemov
2019-05-24 14:00 ` Kirill Tkhai
2019-05-27 23:30 ` Kirill A. Shutemov
2019-05-28 9:15 ` Kirill Tkhai
2019-05-28 16:15 ` Kirill A. Shutemov
2019-05-29 14:33 ` Kirill Tkhai
2019-06-03 14:38 ` Kirill Tkhai
2019-06-03 14:56 ` Kirill Tkhai
2019-06-03 17:47 ` Kirill A. Shutemov
2019-06-04 9:32 ` Kirill Tkhai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=d4664163-35e2-10e0-9c7b-44fa090b7198@virtuozzo.com \
--to=ktkhai@virtuozzo.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=alexander.h.duyck@linux.intel.com \
--cc=andreyknvl@google.com \
--cc=arunks@codeaurora.org \
--cc=cl@linux.com \
--cc=dan.j.williams@intel.com \
--cc=daniel.m.jordan@oracle.com \
--cc=guro@fb.com \
--cc=hannes@cmpxchg.org \
--cc=hughd@google.com \
--cc=ira.weiny@intel.com \
--cc=jannh@google.com \
--cc=jglisse@redhat.com \
--cc=keescook@chromium.org \
--cc=keith.busch@intel.com \
--cc=kilobyte@angband.pl \
--cc=kirill.shutemov@linux.intel.com \
--cc=kirill@shutemov.name \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mgorman@techsingularity.net \
--cc=mhocko@suse.com \
--cc=npiggin@gmail.com \
--cc=riel@surriel.com \
--cc=shakeelb@google.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).