Messages in this thread | | | Date | Mon, 18 Jul 2022 09:59:15 -0400 | Subject | Re: [PATCH] x86/xen: Add support for HVMOP_set_evtchn_upcall_vector | From | Boris Ostrovsky <> |
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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?
-boris
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