Re: [PATCH v5 3/9] mm/mremap: Use pmd/pud_poplulate to update page table entries

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Nathan Chancellor <nathan@kernel.org> writes:

> Hi Aneesh,
>
> On Thu, Apr 22, 2021 at 11:13:17AM +0530, Aneesh Kumar K.V wrote:
>> pmd/pud_populate is the right interface to be used to set the respective
>> page table entries. Some architectures like ppc64 do assume that set_pmd/pud_at
>> can only be used to set a hugepage PTE. Since we are not setting up a hugepage
>> PTE here, use the pmd/pud_populate interface.
>> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>  mm/mremap.c | 7 +++----
>>  1 file changed, 3 insertions(+), 4 deletions(-)
>> 
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index ec8f840399ed..574287f9bb39 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -26,6 +26,7 @@
>>  
>>  #include <asm/cacheflush.h>
>>  #include <asm/tlbflush.h>
>> +#include <asm/pgalloc.h>
>>  
>>  #include "internal.h"
>>  
>> @@ -257,9 +258,8 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>>  	pmd_clear(old_pmd);
>>  
>>  	VM_BUG_ON(!pmd_none(*new_pmd));
>> +	pmd_populate(mm, new_pmd, (pgtable_t)pmd_page_vaddr(pmd));
>>  
>> -	/* Set the new pmd */
>> -	set_pmd_at(mm, new_addr, new_pmd, pmd);
>>  	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
>>  	if (new_ptl != old_ptl)
>>  		spin_unlock(new_ptl);
>> @@ -306,8 +306,7 @@ static bool move_normal_pud(struct vm_area_struct *vma, unsigned long old_addr,
>>  
>>  	VM_BUG_ON(!pud_none(*new_pud));
>>  
>> -	/* Set the new pud */
>> -	set_pud_at(mm, new_addr, new_pud, pud);
>> +	pud_populate(mm, new_pud, (pmd_t *)pud_page_vaddr(pud));
>>  	flush_tlb_range(vma, old_addr, old_addr + PUD_SIZE);
>>  	if (new_ptl != old_ptl)
>>  		spin_unlock(new_ptl);
>> -- 
>> 2.30.2
>> 
>> 
>
> This commit causes my WSL2 VM to close when compiling something memory
> intensive, such as an x86_64_defconfig + CONFIG_LTO_CLANG_FULL=y kernel
> or LLVM/Clang. Unfortunately, I do not have much further information to
> provide since I do not see any sort of splat in dmesg right before it
> closes and I have found zero information about getting the previous
> kernel message in WSL2 (custom init so no systemd or anything).
>
> The config file is the stock one from Microsoft:
>
> https://github.com/microsoft/WSL2-Linux-Kernel/blob/a571dc8cedc8e0e56487c0dc93243e0b5db8960a/Microsoft/config-wsl
>
> I have attached my .config anyways, which includes CONFIG_DEBUG_VM,
> which does not appear to show anything out of the ordinary. I have also
> attached a dmesg just in case anything sticks out. I am happy to provide
> any additional information or perform additional debugging steps as
> needed.
>

Can you try this change?

modified   mm/mremap.c
@@ -279,7 +279,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
 	pmd_clear(old_pmd);
 
 	VM_BUG_ON(!pmd_none(*new_pmd));
-	pmd_populate(mm, new_pmd, (pgtable_t)pmd_page_vaddr(pmd));
+	pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
 
 	if (new_ptl != old_ptl)
 		spin_unlock(new_ptl);