On 2022/4/19 15:37, David Hildenbrand wrote: > On 16.04.22 05:05, 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> >> --- >> v2: >> use special swap entry to avoid permanently mounted swap >> free the bad page in swapcache >> --- >> 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 d112434f85df..03c576111737 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 SWAP_READ_ERROR_NUM 1 >> +#define SWAP_READ_ERROR (MAX_SWAPFILES + SWP_HWPOISON_NUM + \ >> + SWP_MIGRATION_NUM + SWP_DEVICE_NUM + \ >> + SWP_PTE_MARKER_NUM) > > Does anything speak against reusing the hwpoison marker? At least from a > program POV it's similar "the previously well defined content at this > user space address is no longer readable/writable". Looks like a good idea. :) > > I recall that we can just set the pfn to 0 for the hwpoison marker. > > There is e.g., check_hwpoisoned_entry() and it just stops if it finds > "pfn=0". Do you mean that we should set the pfn to 0 for the hwpoison marker so that we can distinguish swapin error case from real hwpoison case? > > Will try to do this in next version. Thanks a lot!
