On 2015-04-13 20:07, Avi Kivity wrote: > On 04/13/2015 08:57 PM, Jan Kiszka wrote: >> On 2015-04-13 19:48, Avi Kivity wrote: >>> I think that Xen does (or did) something along the lines of disabling >>> IST usage (by playing with the descriptors in the IDT) and then >>> re-enabling them when exiting to userspace. >> So we would reuse that active stack for the current IST users until >> then. > > Yes. > >> But I bet there are subtle details that prevent a simple switch at >> IDT level. Hmm, no low-hanging fruit it seems... > > > For sure. It's not insurmountable, but fairly hard. > >>> >>>> [17] http://thread.gmane.org/gmane.comp.emulators.kvm.devel/26712/ >> That thread proposed the complete IST removal. But, given that we still >> have it 7 years later, > > Well, it's not as if a crack team of kernel hackers was laboring night > and day to remove it, but... > >> I suppose that was not very welcome in general. > > Simply removing it is impossible, or an NMI happening immediately after > SYSCALL will hit user-provided %rsp. > >> Thanks, >> Jan >> >> PS: For the Jailhouse readers: we don't use IST. >> > > You don't have userspace, yes? Only guests? Exactly. The day someone adds userspace, I guess I'll have to create a new hypervisor. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
