Messages in this thread | | | From | Andrew Cooper <> | Subject | Re: [PATCH] x86/xen: Add support for HVMOP_set_evtchn_upcall_vector | Date | Mon, 25 Jul 2022 10:08:44 +0000 |
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On 18/07/2022 14:59, Boris Ostrovsky wrote: > > On 7/18/22 4:56 AM, Andrew Cooper wrote: >> 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". > > > The hypercall has been around for a while so I understand ABI concerns > there but XEN_HVM_CPUID_UPCALL_VECTOR was introduced only a month ago. > Why not tie presence of this bit to no longer having to explicitly set > the callback field?
Because that's a breaking change for ~5 years of windows drivers.
~Andrew
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