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

[Miaohe Lin <linmiaohe@huawei.com>]

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?

Thanks.
.