On 2022/1/14 0:48, David Hildenbrand wrote: > On 13.01.22 17:37, Linus Torvalds wrote: >> On Thu, Jan 13, 2022 at 6:39 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: >>> >>> Let's bring Linus in on this, but I think this reintroduces all of the >>> mapcount problems that we've been discussing recently. >>> >>> How about this as an alternative? >> >> No, at that point reuse_swap_page() is the better thing to do. >> >> Don't play games with page_count() (or even worse games with >> swap_count). The page count is only stable if it's 1. Any other value >> means that it can fluctuate due to concurrent lookups, some of which >> can be done locklessly under RCU. > > I'm pretty sure the patch as is will reintroduce the CVE. So I think in Actually, I wonder how reuse_swap_page() in this patch can reintroduce CVE, I think the invoking logic here is as same as that in do_swap_page(). So, could you give me some hint about this? Thanks :) > addition to the reuse_swap_page() check we need more. > > I'm wondering if we can get rid of the mapcount checks in > reuse_swap_page() and instead check for page_count() and swapcount only. > > We don't care if it's unstable in a sense than it will be bigger than > what we expect. In that case we COW as we would already do. > > Thoughts? > -- Best Regards, Liang Zhang
