>>> On 20.04.18 at 17:25, <andrew.cooper3@xxxxxxxxxx> wrote: > On 20/04/18 16:20, Jason Andryuk wrote: >> Adding xen-devel and the Linux Xen maintainers. >> >> Summary: Some Xen users (and maybe others) are hitting a BUG in >> __radix_tree_lookup() under do_swap_page() - example backtrace is >> provided at the end. Matthew Wilcox provided a band-aid patch that >> prints errors like the following instead of triggering the bug. >> >> Skylake 32bit PAE Dom0: >> Bad swp_entry: 80000000 >> mm/swap_state.c:683: bad pte d3a39f1c(8000000400000000) >> >> Ivy Bridge 32bit PAE Dom0: >> Bad swp_entry: 40000000 >> mm/swap_state.c:683: bad pte d3a05f1c(8000000200000000) >> >> Other 32bit DomU: >> Bad swp_entry: 4000000 >> mm/swap_state.c:683: bad pte e2187f30(8000000200000000) >> >> Other 32bit: >> Bad swp_entry: 2000000 >> mm/swap_state.c:683: bad pte ef3a3f38(8000000100000000) >> >> The Linux bugzilla has more info >> https://bugzilla.kernel.org/show_bug.cgi?id=198497 >> >> This may not be exclusive to Xen Linux, but most of the reports are on >> Xen. Matthew wonders if Xen might be stepping on the upper bits of a >> pte. > > Yes - Xen does use the upper bits of a PTE, but only 1 in release > builds, and a second in debug builds. I don't understand where you're > getting the 3rd bit in there. The former supposedly is _PAGE_GUEST_KERNEL, which we use for 64-bit guests only. Above talk is of 32-bit guests only. In addition both this and _PAGE_GNTTAB are used on present PTEs only, while above talk is about swap entries. Jan
