| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <f39be587-31f4-72c0-7d39-dad02a0f5777@redhat.com>
Date: Wed, 14 Jul 2021 18:30:05 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>,
Tiberiu Georgescu <tiberiu.georgescu@...anix.com>
Cc: akpm@...ux-foundation.org, catalin.marinas@....com,
peterz@...radead.org, chinwen.chang@...iatek.com,
linmiaohe@...wei.com, jannh@...gle.com, apopple@...dia.com,
christian.brauner@...ntu.com, ebiederm@...ssion.com,
adobriyan@...il.com, songmuchun@...edance.com, axboe@...nel.dk,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, ivan.teterevkov@...anix.com,
florian.schmidt@...anix.com, carl.waldspurger@...anix.com,
Hugh Dickins <hughd@...gle.com>,
Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC PATCH 1/1] pagemap: report swap location for shared pages
On 14.07.21 18:24, David Hildenbrand wrote:
> On 14.07.21 18:08, Peter Xu wrote:
>> On Wed, Jul 14, 2021 at 03:24:26PM +0000, Tiberiu Georgescu wrote:
>>> When a page allocated using the MAP_SHARED flag is swapped out, its pagemap
>>> entry is cleared. In many cases, there is no difference between swapped-out
>>> shared pages and newly allocated, non-dirty pages in the pagemap interface.
>>>
>>> This patch addresses the behaviour and modifies pte_to_pagemap_entry() to
>>> make use of the XArray associated with the virtual memory area struct
>>> passed as an argument. The XArray contains the location of virtual pages
>>> in the page cache, swap cache or on disk. If they are on either of the
>>> caches, then the original implementation still works. If not, then the
>>> missing information will be retrieved from the XArray.
>>>
>>> Co-developed-by: Florian Schmidt <florian.schmidt@...anix.com>
>>> Signed-off-by: Florian Schmidt <florian.schmidt@...anix.com>
>>> Co-developed-by: Carl Waldspurger <carl.waldspurger@...anix.com>
>>> Signed-off-by: Carl Waldspurger <carl.waldspurger@...anix.com>
>>> Co-developed-by: Ivan Teterevkov <ivan.teterevkov@...anix.com>
>>> Signed-off-by: Ivan Teterevkov <ivan.teterevkov@...anix.com>
>>> Signed-off-by: Tiberiu Georgescu <tiberiu.georgescu@...anix.com>
>>> ---
>>> fs/proc/task_mmu.c | 37 +++++++++++++++++++++++++++++--------
>>> 1 file changed, 29 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>> index eb97468dfe4c..b17c8aedd32e 100644
>>> --- a/fs/proc/task_mmu.c
>>> +++ b/fs/proc/task_mmu.c
>>> @@ -1359,12 +1359,25 @@ static int pagemap_pte_hole(unsigned long start, unsigned long end,
>>> return err;
>>> }
>>>
>>> +static void *get_xa_entry_at_vma_addr(struct vm_area_struct *vma,
>>> + unsigned long addr)
>>> +{
>>> + struct inode *inode = file_inode(vma->vm_file);
>>> + struct address_space *mapping = inode->i_mapping;
>>> + pgoff_t offset = linear_page_index(vma, addr);
>>> +
>>> + return xa_load(&mapping->i_pages, offset);
>>> +}
>>> +
>>> static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
>>> struct vm_area_struct *vma, unsigned long addr, pte_t pte)
>>> {
>>> u64 frame = 0, flags = 0;
>>> struct page *page = NULL;
>>>
>>> + if (vma->vm_flags & VM_SOFTDIRTY)
>>> + flags |= PM_SOFT_DIRTY;
>>> +
>>> if (pte_present(pte)) {
>>> if (pm->show_pfn)
>>> frame = pte_pfn(pte);
>>> @@ -1374,13 +1387,22 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
>>> flags |= PM_SOFT_DIRTY;
>>> if (pte_uffd_wp(pte))
>>> flags |= PM_UFFD_WP;
>>> - } else if (is_swap_pte(pte)) {
>>> + } else if (is_swap_pte(pte) || shmem_file(vma->vm_file)) {
>>> swp_entry_t entry;
>>> - if (pte_swp_soft_dirty(pte))
>>> - flags |= PM_SOFT_DIRTY;
>>> - if (pte_swp_uffd_wp(pte))
>>> - flags |= PM_UFFD_WP;
>>> - entry = pte_to_swp_entry(pte);
>>> + if (is_swap_pte(pte)) {
>>> + entry = pte_to_swp_entry(pte);
>>> + if (pte_swp_soft_dirty(pte))
>>> + flags |= PM_SOFT_DIRTY;
>>> + if (pte_swp_uffd_wp(pte))
>>> + flags |= PM_UFFD_WP;
>>> + } else {
>>> + void *xa_entry = get_xa_entry_at_vma_addr(vma, addr);
>>> +
>>> + if (xa_is_value(xa_entry))
>>> + entry = radix_to_swp_entry(xa_entry);
>>> + else
>>> + goto out;
>>> + }
>>> if (pm->show_pfn)
>>> frame = swp_type(entry) |
>>> (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
>>> @@ -1393,9 +1415,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
>>> flags |= PM_FILE;
>>> if (page && page_mapcount(page) == 1)
>>> flags |= PM_MMAP_EXCLUSIVE;
>>> - if (vma->vm_flags & VM_SOFTDIRTY)
>>> - flags |= PM_SOFT_DIRTY;
>>
>> IMHO moving this to the entry will only work for the initial iteration, however
>> it won't really help anything, as soft-dirty should always be used in pair with
>> clear_refs written with value "4" first otherwise all pages will be marked
>> soft-dirty then the pagemap data is meaningless.
>>
>> After the "write 4" op VM_SOFTDIRTY will be cleared and I expect the test case
>> to see all zeros again even with the patch.
>>
>> I think one way to fix this is to do something similar to uffd-wp: we leave a
>> marker in pte showing that this is soft-dirtied pte even if swapped out.
>
> How exactly does such a pte look like? Simply pte_none() with another
> bit set?
>
>> However we don't have a mechanism for that yet in current linux, and the
>> uffd-wp series is the first one trying to introduce something like that.
>
> Can you give me a pointer? I'm very interested in learning how to
> identify this case.
>
I assume it's
https://lore.kernel.org/lkml/20210527202117.30689-1-peterx@redhat.com/
--
Thanks,
David / dhildenb
Powered by blists - more mailing lists