On 2022/4/25 16:01, David Hildenbrand wrote: > On 25.04.22 09:55, ying.huang@xxxxxxxxx wrote: >> On Mon, 2022-04-25 at 09:49 +0200, David Hildenbrand wrote: >>> On 25.04.22 09:41, ying.huang@xxxxxxxxx wrote: >>>> Hi, Miaohe, >>>> >>>> On Sun, 2022-04-24 at 17:11 +0800, Miaohe Lin wrote: >>>>> 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. >>>>> >>>>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>>>> Acked-by: David Hildenbrand <david@xxxxxxxxxx> >>>>> --- >>>>> include/linux/swap.h | 7 ++++++- >>>>> include/linux/swapops.h | 10 ++++++++++ >>>>> mm/memory.c | 5 ++++- >>>>> mm/swapfile.c | 11 +++++++++++ >>>>> 4 files changed, 31 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/include/linux/swap.h b/include/linux/swap.h >>>>> index 5553189d0215..b82c196d8867 100644 >>>>> --- a/include/linux/swap.h >>>>> +++ b/include/linux/swap.h >>>>> @@ -55,6 +55,10 @@ static inline int current_is_kswapd(void) >>>>> * actions on faults. >>>>> */ >>>>> >>>>> +#define SWP_SWAPIN_ERROR_NUM 1 >>>>> +#define SWP_SWAPIN_ERROR (MAX_SWAPFILES + SWP_HWPOISON_NUM + \ >>>>> + SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \ >>>>> + SWP_PTE_MARKER_NUM) >>>>> >>>>> >>>> >>>> It appears wasteful to use another swap device number. >>> >>> Do we really care? >>> >>> We currently use 5 bits for swap types, so we have a total of 32. >>> >>> SWP_HWPOISON_NUM -> 1 >>> SWP_MIGRATION_NUM -> 3 >>> SWP_PTE_MARKER_NUM -> 1 >>> SWP_DEVICE_NUM -> 4 >>> SWP_SWAPIN_ERROR_NUM -> 1 >>> >>> Which would leave us with 32 - 10 = 22 swap devices. IMHO that's plenty >>> for real life scenarios. >> >> Creating multiple swap partitions on one disk can improve the >> scalability of swap subsystem, although we usually don't have so many >> disks for swap. > > Exactly, and IMHO if we have 22 or 23 doesn't make a real difference > here ... I tend to agree with David. Thanks both! >
