At 13:40 +0100 on 09 Jun (1307626812), Stefano Stabellini wrote: > CC'ing xen-devel and Tim. > > This is a comment from a previous email in the thread: > > > It most easily reproduced only on xen hvm 32bit guest under heavy vcpus > > contention for real cpus resources (i.e. I had to overcommit cpus and > > run several cpu hog tasks on host to make guest crash on reboot cycle). > > And from last experiments, crash happens only on on hosts that doesn't > > have hap feature or if hap is disabled in hypervisor. > > it makes me think that it is a shadow pagetables bug; see details below. > You can find more details on it following this thread on the lkml. Oh dear. I'm having a look at the linux code now to try and understand the behaviour. In the meantime, what version of Xen was this on? If you're willing to try recompiling Xen with some small patches that disable the "cleverer" parts of the shadow pagetable code that might indicate something. (Of course, it might just change the timing to obscure a real linux bug too.) The only time I've seen a corruption like this, with a mapping transiently going to the wrong frame, it turned out to be caused by 32-bit pagetable-handling code writing a PAE PTE with a single 64-bit write (which is not atomic on x86-32), and the TLB happening to see the intermediate, half-written entry. I doubt that there's any bug like that in linux, though, or we'd surely have seen it before now. Cheers, Tim. -- Tim Deegan <Tim.Deegan@xxxxxxxxxx> Principal Software Engineer, Xen Platform Team Citrix Systems UK Ltd. (Company #02937203, SL9 0BG) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>