Messages in this thread | | | Subject | Re: WARNING: can't access registers at asm_common_interrupt | From | Jürgen Groß <> | Date | Sun, 15 Nov 2020 17:13:55 +0100 |
| |
On 15.11.20 17:05, Andy Lutomirski wrote: > >> On Nov 14, 2020, at 10:33 PM, Jürgen Groß <jgross@suse.com> wrote: >> >> On 14.11.20 19:10, Andy Lutomirski wrote: >>>> On Sat, Nov 14, 2020 at 1:16 AM Jürgen Groß <jgross@suse.com> wrote: >>>> >>>> On 13.11.20 18:34, Andy Lutomirski wrote: >>>>> On Wed, Nov 11, 2020 at 12:25 PM Andrew Cooper >>>>> <andrew.cooper3@citrix.com> wrote: >>>>> >>>>> So I think there is at most one of these that wants anything more >>>>> complicated than a plain ALTERNATIVE. Any volunteers to make it so? >>>>> Juergen, if you do all of them except USERGS_SYSRET64, I hereby >>>>> volunteer to do that one. >>>> >>>> Why is a plain alternative (either swapgs; sysretq or a jmp xen_sysret64 >>>> depending on X86_FEATURE_XENPV) no option? >>>> >>>> Its not as if this code would run before alternative patching. >>> ALTERNATIVE would "work" in the sense that it would function and be >>> just about as nonsensical as the current code. Fundamentally, Xen >>> PV's sysret feature is not a drop-in replacement for SYSRET64, and >>> pretending that it is seems unlikely to work well. I suspect that the >>> current code is some combination of exceedingly slow, non-functional, >>> and incorrect in subtle ways. >>> We should just have a separate Xen PV exit path the same way we have a >>> separate entry path in recent kernels. *This* is what I'm >>> volunteering to do. >> >> I don't think there is much work needed. Xen PV does basically a return >> to user mode via IRET. I think it might work just to use >> swapgs_restore_regs_and_return_to_usermode() unconditionally for Xen PV. >> > > I’m quite confident that will work, but I was hoping to get it to work quickly too :)
The PV interface requires to use the iret hypercall, because there is no sysret equivalent.
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |