On 29/08/18 12:00, Olaf Hering wrote: > On Wed, Aug 29, Andrew Cooper wrote: > >> Architecturally speaking, handing #MC back is probably the closest we >> can get to sensible behaviour, but it is still a bug that Linux is >> touching the ballooned out page in the first place. > Well, the issue is that a read crosses a page boundary. If that would be > forbidden, load_unaligned_zeropad() would not exist. It can not know > what is in the following page. And such page crossing happens also in > the unballooned case. Sadly I can not trigger the reported NFS bug > myself. But it can be enforced by ballooning enough pages so that an > allocated readdir reply eventually is right in front of a ballooned > page.
The Linux bug is not shooting the ballooned page out of the directmap. Linux should be taking a fatal #PF for that read, because its a virtual mapping for a frame which Linux has voluntarily elected to make invalid. As Xen can't prevent Linux from making/maintaining such an invalid mapping, throwing #MC back is the next best thing, because terminating the access with ~0 is just going to hide the bug, and run at a glacial pace while doing so. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
