kernel: xen: Xen hypercall page unsafe against speculative attacks (Xen Security Advisory 466)

In the Linux kernel, the following vulnerability has been resolved: x86/xen: don't do PV iret hypercall through hypercall page Instead of jumping to the Xen hypercall page for doing the iret hypercall, directly code the required sequence in xen-asm.S. This is done in preparation of no longer usin...