Messages in this thread | | | From | Andrew Cooper <> | Subject | Re: [PATCH] x86/xen: Add support for HVMOP_set_evtchn_upcall_vector | Date | Mon, 18 Jul 2022 08:56:02 +0000 |
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On 15/07/2022 14:10, Boris Ostrovsky wrote: > > On 7/15/22 5:50 AM, Andrew Cooper wrote: >> On 15/07/2022 09:18, Jane Malalane wrote: >>> On 14/07/2022 00:27, Boris Ostrovsky wrote: >>>>> xen_hvm_smp_init(); >>>>> WARN_ON(xen_cpuhp_setup(xen_cpu_up_prepare_hvm, >>>>> xen_cpu_dead_hvm)); >>>>> diff --git a/arch/x86/xen/suspend_hvm.c b/arch/x86/xen/suspend_hvm.c >>>>> index 9d548b0c772f..be66e027ef28 100644 >>>>> --- a/arch/x86/xen/suspend_hvm.c >>>>> +++ b/arch/x86/xen/suspend_hvm.c >>>>> @@ -5,6 +5,7 @@ >>>>> #include <xen/hvm.h> >>>>> #include <xen/features.h> >>>>> #include <xen/interface/features.h> >>>>> +#include <xen/events.h> >>>>> #include "xen-ops.h" >>>>> @@ -14,6 +15,23 @@ void xen_hvm_post_suspend(int suspend_cancelled) >>>>> xen_hvm_init_shared_info(); >>>>> xen_vcpu_restore(); >>>>> } >>>>> - xen_setup_callback_vector(); >>>>> + if (xen_ack_upcall) { >>>>> + unsigned int cpu; >>>>> + >>>>> + for_each_online_cpu(cpu) { >>>>> + xen_hvm_evtchn_upcall_vector_t op = { >>>>> + .vector = HYPERVISOR_CALLBACK_VECTOR, >>>>> + .vcpu = per_cpu(xen_vcpu_id, cpu), >>>>> + }; >>>>> + >>>>> + BUG_ON(HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, >>>>> + &op)); >>>>> + /* Trick toolstack to think we are enlightened. */ >>>>> + if (!cpu) >>>>> + BUG_ON(xen_set_callback_via(1)); >>>> What are you trying to make the toolstack aware of? That we have *a* >>>> callback (either global or percpu)? >>> Yes, specifically for the check in libxl__domain_pvcontrol_available. >> And others. >> >> This is all a giant bodge, but basically a lot of tooling uses the >> non-zero-ness of the CALLBACK_VIA param to determine whether the VM has >> Xen-aware drivers loaded or not. >> >> The value 1 is a CALLBACK_VIA value which encodes GSI 1, and the only >> reason this doesn't explode everywhere is because the >> evtchn_upcall_vector registration takes priority over GSI delivery. >> >> This is decades of tech debt piled on top of tech debt. > > > Feels like it (setting the callback parameter) is something that the > hypervisor should do --- no need to expose guests to this.
Sensible or not, it is the ABI.
Linux still needs to work (nicely) with older Xen's in the world, and we can't just retrofit a change in the hypervisor which says "btw, this ABI we've just changed now has a side effect of modifying a field that you also logically own".
~Andrew
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