On 19.04.22 09:29, Miaohe Lin wrote: > On 2022/4/19 11:51, Alistair Popple wrote: >> Miaohe Lin <linmiaohe@xxxxxxxxxx> writes: >> >>> There is a bug in unuse_pte(): when swap page happens to be unreadable, >>> page filled with random data is mapped into user address space. In case >>> of error, a special swap entry indicating swap read fails is set to the >>> page table. So the swapcache page can be freed and the user won't end up >>> with a permanently mounted swap because a sector is bad. And if the page >>> is accessed later, the user process will be killed so that corrupted data >>> is never consumed. On the other hand, if the page is never accessed, the >>> user won't even notice it. >> >> Hi Miaohe, >>> It seems we're not actually using the pfn that gets stored in the special swap >> entry here. Is my understanding correct? If so I think it would be better to use > > Yes, you're right. The pfn is not used now. What we need here is a special swap entry > to do the right things. I think we can change to store some debugging information instead > of pfn if needed in the future. > >> the new PTE markers Peter introduced[1] rather than adding another swap entry >> type. > > IIUC, we should not reuse that swap entry here. From definition: > > PTE markers > =========== > ... > PTE marker is a new type of swap entry that is ony applicable to file > backed memories like shmem and hugetlbfs. It's used to persist some > pte-level information even if the original present ptes in pgtable are > zapped. > > It's designed for file backed memories while swapin error entry is for anonymous > memories. And there has some differences in processing. So it's not a good idea > to reuse pte markers. Or am I miss something? I tend to agree. As raised in my other reply, maybe we can simply reuse hwpoison entries and update the documentation of them accordingly. -- Thanks, David / dhildenb
