Re: [PATCH v9 02/10] mm: Non-pmd-mappable, large folios for folio_add_new_anon_rmap()

[David Hildenbrand <david@redhat.com>]

On 13.01.24 23:42, Jiri Olsa wrote:
> On Thu, Dec 07, 2023 at 04:12:03PM +0000, Ryan Roberts wrote:
>> In preparation for supporting anonymous multi-size THP, improve
>> folio_add_new_anon_rmap() to allow a non-pmd-mappable, large folio to be
>> passed to it. In this case, all contained pages are accounted using the
>> order-0 folio (or base page) scheme.
>>
>> Reviewed-by: Yu Zhao <yuzhao@google.com>
>> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> Reviewed-by: Barry Song <v-songbaohua@oppo.com>
>> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> Tested-by: John Hubbard <jhubbard@nvidia.com>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>> ---
>>   mm/rmap.c | 28 ++++++++++++++++++++--------
>>   1 file changed, 20 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 2a1e45e6419f..846fc79f3ca9 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1335,32 +1335,44 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
>>    * This means the inc-and-test can be bypassed.
>>    * The folio does not have to be locked.
>>    *
>> - * If the folio is large, it is accounted as a THP.  As the folio
>> + * If the folio is pmd-mappable, it is accounted as a THP.  As the folio
>>    * is new, it's assumed to be mapped exclusively by a single process.
>>    */
>>   void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>>   		unsigned long address)
>>   {
>> -	int nr;
>> +	int nr = folio_nr_pages(folio);
>>   
>> -	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
>> +	VM_BUG_ON_VMA(address < vma->vm_start ||
>> +			address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
> 
> hi,
> I'm hitting this bug (console output below) with adding uprobe
> on simple program like:
> 
>    $ cat up.c
>    int main(void)
>    {
>       return 0;
>    }
> 
>    # bpftrace -e 'uprobe:/home/jolsa/up:_start {}'
> 
>    $ ./up
> 
> it's on top of current linus tree master:
>    052d534373b7 Merge tag 'exfat-for-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat
> 
> before this patch it seems to work, I can send my .config if needed

bpf only inserts a small folio, so no magic there.

It was:
	VM_BUG_ON_VMA(address < vma->vm_start || address >= vma->vm_end, vma);
And now it is
	VM_BUG_ON_VMA(address < vma->vm_start || address + (nr << PAGE_SHIFT) > vma->vm_end, vma);

I think this change is sane. As long as the address is aligned to full pages
(which it better should be)

Staring at uprobe_write_opcode, likely vaddr isn't aligned ...

Likely (hopefully) that is not an issue for __folio_set_anon(), because linear_page_index()
will mask these bits off.


Would the following change fix it for you?

 From c640a8363e47bc96965a35115a040b5f876c4320 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Sun, 14 Jan 2024 18:32:57 +0100
Subject: [PATCH] tmp

Signed-off-by: David Hildenbrand <david@redhat.com>
---
  kernel/events/uprobes.c | 2 +-
  mm/rmap.c               | 1 +
  2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 485bb0389b488..929e98c629652 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -537,7 +537,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
  		}
  	}
  
-	ret = __replace_page(vma, vaddr, old_page, new_page);
+	ret = __replace_page(vma, vaddr & PAGE_MASK, old_page, new_page);
  	if (new_page)
  		put_page(new_page);
  put_old:
diff --git a/mm/rmap.c b/mm/rmap.c
index f5d43edad529a..a903db4df6b97 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1408,6 +1408,7 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
  {
  	int nr = folio_nr_pages(folio);
  
+	VM_WARN_ON_FOLIO(!IS_ALIGNED(address, PAGE_SIZE), folio);
  	VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
  	VM_BUG_ON_VMA(address < vma->vm_start ||
  			address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
-- 
2.43.0



-- 
Cheers,

David / dhildenb


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