[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] trap/interrupt gate for hypercall
On 15/5/07 16:18, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: >> Everything's an interrupt gate on 32-bit Xen, so that we can safely >> (atomically) save away guest segment register state. NMI is the only real >> pain, and I suppose MCE too. Coincidentally Jan just emailed about this >> very point. > > So why is atomic save required for hypercall here? NMI can break > atomic save here for both types, as you said. Normally external > interrupt handler doesn't need communicate with interrupted > context. So even when an external interrupt comes in the middle > of the guest context save for hypercall (if by trap gate), that > interrupted save process can still continue since interrupt handler > itself will impose atomic context save/restore on top of interrupted > context. Interrupt handlers save and restore segment registers. We could fault on a reload of a segment register and lose the original segment register value. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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