[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] RFC Userspace hypercalls
>>> On 06.01.16 at 12:44, <andrew.cooper3@xxxxxxxxxx> wrote: > The HVM ABI (for whatever reason) unilaterally fails > a userspace hypercall with -EPERM, making it impossible for the kernel > to trap-and-forward even it wanted to. Perhaps just to match PV behavior? > There are already scenarios under test where we cannot rely on the test > kernel having a fully functioning set of entry points (e.g. the DPL part > of the test above). Therefore I specifically want to make it possible > to make userspace hypercalls, rather than simply making them possible to > be trapped-and-forwarded. > > > As a result, I proposing introducing a hypercall which allows a domain > to adjust its entry criteria for hypercalls (e.g. set_hypercall_iopl). > Doing this for HVM guests is straight forward, but PV guests are harder, > as they bounce through Xen entrypoints. The primary question I have is whether this proposal is going to be of use to anything other than your test framework (i.e. namely any "ordinary" guests). A second question then would be whether the PV case really needs to be handled. > For PV guests, I propose that userspace hypercalls get implemented with > the int $0x82 path exclusively. i.e. enabling userspace hypercalls > causes the hypercall page writing logic to consider the guest a ring1 > kernel, and the int $0x82 entrypoint suitably delegates between a > regular hypercall and a compat hypercall. With int $0x82 being the primary hypercall path for 32-bit guests, I'd be concerned of any code addition, especially that of further conditionals. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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