Messages in this thread | | | Date | Wed, 22 Jun 2022 16:50:21 -0500 | Subject | Re: [PATCH 1/2] x86: notify hypervisor about guest entering s2idle state | From | "Limonciello, Mario" <> |
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On 6/22/2022 04:53, Grzegorz Jaszczyk wrote: > pon., 20 cze 2022 o 18:32 Limonciello, Mario > <mario.limonciello@amd.com> napisał(a): >> >> On 6/20/2022 10:43, Grzegorz Jaszczyk wrote: >>> czw., 16 cze 2022 o 18:58 Limonciello, Mario >>> <mario.limonciello@amd.com> napisał(a): >>>> >>>> On 6/16/2022 11:48, Sean Christopherson wrote: >>>>> On Wed, Jun 15, 2022, Grzegorz Jaszczyk wrote: >>>>>> pt., 10 cze 2022 o 16:30 Sean Christopherson <seanjc@google.com> napisał(a): >>>>>>> MMIO or PIO for the actual exit, there's nothing special about hypercalls. As for >>>>>>> enumerating to the guest that it should do something, why not add a new ACPI_LPS0_* >>>>>>> function? E.g. something like >>>>>>> >>>>>>> static void s2idle_hypervisor_notify(void) >>>>>>> { >>>>>>> if (lps0_dsm_func_mask > 0) >>>>>>> acpi_sleep_run_lps0_dsm(ACPI_LPS0_EXIT_HYPERVISOR_NOTIFY >>>>>>> lps0_dsm_func_mask, lps0_dsm_guid); >>>>>>> } >>>>>> >>>>>> Great, thank you for your suggestion! I will try this approach and >>>>>> come back. Since this will be the main change in the next version, >>>>>> will it be ok for you to add Suggested-by: Sean Christopherson >>>>>> <seanjc@google.com> tag? >>>>> >>>>> If you want, but there's certainly no need to do so. But I assume you or someone >>>>> at Intel will need to get formal approval for adding another ACPI LPS0 function? >>>>> I.e. isn't there work to be done outside of the kernel before any patches can be >>>>> merged? >>>> >>>> There are 3 different LPS0 GUIDs in use. An Intel one, an AMD (legacy) >>>> one, and a Microsoft one. They all have their own specs, and so if this >>>> was to be added I think all 3 need to be updated. >>> >>> Yes this will not be easy to achieve I think. >>> >>>> >>>> As this is Linux specific hypervisor behavior, I don't know you would be >>>> able to convince Microsoft to update theirs' either. >>>> >>>> How about using s2idle_devops? There is a prepare() call and a >>>> restore() call that is set for each handler. The only consumer of this >>>> ATM I'm aware of is the amd-pmc driver, but it's done like a >>>> notification chain so that a bunch of drivers can hook in if they need to. >>>> >>>> Then you can have this notification path and the associated ACPI device >>>> it calls out to be it's own driver. >>> >>> Thank you for your suggestion, just to be sure that I've understand >>> your idea correctly: >>> 1) it will require to extend acpi_s2idle_dev_ops about something like >>> hypervisor_notify() call, since existing prepare() is called from end >>> of acpi_s2idle_prepare_late so it is too early as it was described in >>> one of previous message (between acpi_s2idle_prepare_late and place >>> where we use hypercall there are several places where the suspend >>> could be canceled, otherwise we could probably try to trap on other >>> acpi_sleep_run_lps0_dsm occurrence from acpi_s2idle_prepare_late). >>> >> >> The idea for prepare() was it would be the absolute last thing before >> the s2idle loop was run. You're sure that's too early? It's basically >> the same thing as having a last stage new _DSM call. >> >> What about adding a new abort() extension to acpi_s2idle_dev_ops? Then >> you could catch the cancelled suspend case still and take corrective >> action (if that action is different than what restore() would do). > > It will be problematic since the abort/restore notification could > arrive too late and therefore the whole system will go to suspend > thinking that the guest is in desired s2ilde state. Also in this case > it would be impossible to prevent races and actually making sure that > the guest is suspended or not. We already had similar discussion with > Sean earlier in this thread why the notification have to be send just > before swait_event_exclusive(s2idle_wait_head, s2idle_state == > S2IDLE_STATE_WAKE) and that the VMM have to have control over guest > resumption. > > Nevertheless if extending acpi_s2idle_dev_ops is possible, why not > extend it about the hypervisor_notify() and use it in the same place > where the hypercall is used in this patch? Do you see any issue with > that?
If this needs to be a hypercall and the hypercall needs to go at that specific time, I wouldn't bother with extending acpi_s2idle_dev_ops. The whole idea there was that this would be less custom and could follow a spec.
TBH - given the strong dependency on being the very last command and this being all Linux specific (you won't need to do something similar with Windows) - I think the way you already did it makes the most sense. It seems to me the ACPI device model doesn't really work well for this scenario.
> >> >>> 2) using newly introduced acpi_s2idle_dev_ops hypervisor_notify() call >>> will allow to register handler from Intel x86/intel/pmc/core.c driver >>> and/or AMD x86/amd-pmc.c driver. Therefore we will need to get only >>> Intel and/or AMD approval about extending the ACPI LPS0 _DSM method, >>> correct? >>> >> >> Right now the only thing that hooks prepare()/restore() is the amd-pmc >> driver (unless Intel's PMC had a change I didn't catch yet). >> >> I don't think you should be changing any existing drivers but rather >> introduce another platform driver for this specific case. >> >> So it would be something like this: >> >> acpi_s2idle_prepare_late >> -> prepare() >> --> AMD: amd_pmc handler for prepare() >> --> Intel: intel_pmc handler for prepare() (conceptual) >> --> HYPE0001 device: new driver's prepare() routine >> >> So the platform driver would match the HYPE0001 device to load, and it >> wouldn't do anything other than provide a prepare()/restore() handler >> for your case. >> >> You don't need to change any existing specs. If anything a new spec to >> go with this new ACPI device would be made. Someone would need to >> reserve the ID and such for it, but I think you can mock it up in advance. > > Thank you for your explanation. This means that I should register > "HYPE" through https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fuefi.org%2FPNP_ACPI_Registry&data=05%7C01%7Cmario.limonciello%40amd.com%7C49512293908e4ee17e8c08da54351ed5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637914884458918039%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v5VsnxAINiJhOMLpwORLHd13WcYBHf%2FGSNv8Bjhyino%3D&reserved=0 before introducing > this new driver to Linux. > I have no experience with the above, so I wonder who should be > responsible for maintaining such ACPI ID since it will not belong to > any specific vendor? There is an example of e.g. COREBOOT PROJECT > using "BOOT" ACPI ID [1], which seems similar in terms of not > specifying any vendor but rather the project as a responsible entity. > Maybe you have some recommendations?
Maybe LF could own a namespace and ID? But I would suggest you make a mockup that everything works this way before you go explore too much.
Also make sure Rafael is aligned with your mockup.
> > I am also not sure if and where a specification describing such a > device has to be maintained. Since "HYPE0001" will have its own _DSM > so will it be required to document it somewhere rather than just using > it in the driver and preparing proper ACPI tables for guest? > >> >>> I wonder if this will be affordable so just re-thinking loudly if >>> there is no other mechanism that could be suggested and used upstream >>> so we could notify hypervisor/vmm about guest entering s2idle state? >>> Especially that such _DSM function will be introduced only to trap on >>> some fake MMIO/PIO access and will be useful only for guest ACPI >>> tables? >>> >> >> Do you need to worry about Microsoft guests using Modern Standby too or >> is that out of the scope of your problem set? I think you'll be a lot >> more limited in how this can behave and where you can modify things if so. >> > > I do not need to worry about Microsoft guests.
Makes life a lot easier :)
> > [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fuefi.org%2Facpi_id_list&data=05%7C01%7Cmario.limonciello%40amd.com%7C49512293908e4ee17e8c08da54351ed5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637914884458918039%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=TXdPO%2BlCHa6v37IBsyymhGztgxZn6GEVESM%2FYI5LuUc%3D&reserved=0 > > Thank you, > Grzegorz
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