Re: [PATCH 1/2] mm: support poison recovery from do_cow_fault()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/9/10 9:58, Miaohe Lin wrote:
> On 2024/9/6 10:42, Kefeng Wang wrote:
>> Like commit a873dfe1032a ("mm, hwpoison: try to recover from copy-on
>> write faults"), there is another path which could crash because it does
>> not have recovery code where poison is consumed by the kernel in
>> do_cow_fault(), a crash calltrace shown below on old kernel, but it
>> could be happened in the lastest mainline code,
>>
>>    CPU: 7 PID: 3248 Comm: mpi Kdump: loaded Tainted: G           OE     5.10.0 #1
>>    pc : copy_page+0xc/0xbc
>>    lr : copy_user_highpage+0x50/0x9c
>>    Call trace:
>>      copy_page+0xc/0xbc
>>      do_cow_fault+0x118/0x2bc
>>      do_fault+0x40/0x1a4
>>      handle_pte_fault+0x154/0x230
>>      __handle_mm_fault+0x1a8/0x38c
>>      handle_mm_fault+0xf0/0x250
>>      do_page_fault+0x184/0x454
>>      do_translation_fault+0xac/0xd4
>>      do_mem_abort+0x44/0xbc
>>
>> Fix it by using copy_mc_user_highpage() to handle this case and return
>> VM_FAULT_HWPOISON for cow fault.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> ---
>>   mm/memory.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 42674c0748cb..d310c073a1b3 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -5089,7 +5089,10 @@ static vm_fault_t do_cow_fault(struct vm_fault *vmf)
>>   	if (ret & VM_FAULT_DONE_COW)
>>   		return ret;
>>   
>> -	copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
>> +	if (copy_mc_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma)) {
>> +		ret = VM_FAULT_HWPOISON;
>> +		goto uncharge_out;
>> +	}
> 
> When copy_mc_user_highpage fails, we should have vmf->page locked and hold the extra refcnt
> of vmf->page. So we should call unlock_page(vmf->page) and put_page(vmf->page) before goto
> uncharge_out?
> 

Right, for upstream, we need to more handling for vmf->page, will fix, 
thanks.

> Thanks.
> .