On Thu, Aug 02, 2018 at 11:18:08AM +0200, Igor Mammedov wrote: > On Thu, 26 Jul 2018 19:09:22 +0300 > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > On Wed, Jul 25, 2018 at 05:53:35PM +0200, Igor Mammedov wrote: > > > On Wed, 25 Jul 2018 15:44:37 +0300 > > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > > > > > On Wed, Jul 25, 2018 at 02:32:11PM +0200, Igor Mammedov wrote: > > > > > On Tue, 10 Jul 2018 03:01:30 +0300 > > > > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > > > > > > > > > Now that basic support for guest CPU PM is upstream, I started > > > > > > looking > > > > > > for making it migrateable. Since a VM can be migrated between > > > > > > different > > > > > > hosts, PM info needs to change each time with move the VM to a > > > > > > different > > > > > > host. > > > > > Considering notification is async, so there will be a window when > > > > > guest will be using old Cstates on new host. What will happen if > > > > > machine is migrated to host that doesn't support a Cstate > > > > > that was used on source when guest was started? > > > > > > > > My testing shows mwait with a wrong hint works, presumably it just uses > > > > a lot of power. > > > > > > > > > > This adds infrastructure - based on Load/Unload - to support exactly > > > > > > that: QEMU generates AML (changing it on migration) and stores it in > > > > > > reserved memory, OSPM loads _CST from there on demand. > > > > > Cool and very tempting idea but I have 2 worries about this approach: > > > > > 1. How well does it work with Windows based guests? > > > > > (I've tried something similar but generating new AML from AML > > > > > itself > > > > > to get rid of our long if/else chains there to make up Notify > > > > > target name. > > > > > I ditched it (unfortunately I don't recall why) ) > > > > > > > > After trying it, I can tell you why - it's a horrid mess of > > > > unreadable code, with arbitrary restraints on package > > > > length etc. > > > in my case it was only 4 character NameString, but Windows probably > > > wasn't happy or just ignored it. > > > Considering recent development (TPM series) it might have been issue > > > with SYSTEM_MEMORY not working properly if used as byte buffer field. > > > > > > Even if it's an unreadable mess it's still stable mess and very > > > constrained > > > one within a single firmware blob that came from source. > > > > That's exectly the argument we had for keeping ACPI > > generation in bios. It's just not an interface that scales. > > > > > Hence it's more preferable than split brain in this series. > > > > > > But I don't think we even need dynamic AML for _CST usecase at all, > > > existing cpuhp interface should work just fine for it and should be > > > simpler as all infrastructure is already there. > > > > Not sure I get what you mean. Could you post a patch? > > > > > > > 2. (probably biggest issue) Loading dynamically generated AML > > > > > basically would make all AML code ABI, so that static AML > > > > > in RAM of old QEMU version would match dynamic generated > > > > > one on target side with new QEMU (/me generalizing approach beyond > > > > > _CST support). > > > > > I'd try to keep our AML version less as much as possible > > > > > and go this route only if there is no other way to do it. > > > > > > > > That's a good point, thanks for bringing this up! > > > > > > > > So it seems that we will need to define the ABI, yes. All AML code is > > > > an over-statement though, there are specific entry points > > > > we must maintain, right? > > > Well, I'm rather unsure what and where could break, > > > hence I'm afraid of a new beast and it probably won't be easy > > > to convince me that ABI would be able to keep things manageable > > > and stable. > > > Considering big amount of AML code that we already have > > > I'm not confident eye balling during review and testing the latest > > > firmware/qemu would be sufficient as we suddenly would have exploded > > > test matrix where firmware in use is a mixed from old/and new parts. > > > > Well there's one exported method so far and it relies on one container > > device in static table set which does not sound too hard to keep stable. > > > > Given how simple the dynamic table is, how about just checking it > > with a unit test? It is literally a single return statement. > > If it returns a valid package, that is all that we > > care about. I can write some firmware to test that constraint. > > > > > > > > And that in the end isn't fundamentally different from the ABIs > > > > mandated by the ACPI spec. > > > > > > > > So I have these ideas to try to mitigate the issues: > > > > - document the ABI (like we have in the ACPI spec) > > > > - use a specific prefix for all external calls (like _ for ACPI spec > > > > ones) > > > > - use a specific (different) prefix for all internal loaded calls (like > > > > [A-Z] for non-ACPI spec ones) > > > ACPI spec horrible mess and bad example (even committee isn't able to > > > keep it consistent) > > > but it's necessary evil (compared to no spec at all). > > > Adding ABI requirement will complicate coding/reviewing for > > > already complex AML compared to current non ABI way. > > > Hence from maintainability POV we should stay away from this approach > > > if there is a viable alternative. > > > > I agree. Not that I see one. > > I'll try to come up with a patch to make use of cpuhp registers > to pass CST values and it's AML counterpart. > Then you'd need to just wire it up to whatever means you use > to get these values from host. > > BTW: > I've noticed you have used SystemIO registers in CST > (my patch used FFH registers) using mmio defeats purpose > as it causes guest exit instead of mwait that we are targeting. > > Is it just for demo purpose of RFC with new AML interface?
Just a demo. Actual mwait will need linux changes to make linux obey acpi if it conflicts with cpuid. > > > > > > > > > > Thoughts? > > > > > > > > > > This is a partially functional prototype. > > > > > > > > > > > > What works: > > > > > > loading _CST dynamically and reporting it to OSPM > > > > > > > > > > > > What doesn't: > > > > > > detecting host configuration and generating correct _CST package > > > > > > notifying guest about the change to trigger _CST re-evaluation > > > > > > disabling mwait/halt exists as appropriate > > > > > > > > > > > > Michael S. Tsirkin (6): > > > > > > acpi: aml: add aml_register() > > > > > > acpi: generalize aml_package / aml_varpackage > > > > > > acpi: aml_load/aml_unload > > > > > > acpi: export acpi_checksum > > > > > > acpi: init header without linking > > > > > > acpi: aml generation for _CST > > > > > > pc: HACK: acpi: tie in _CST object to Processor > > > > > > > > > > > > include/hw/acpi/acpi.h | 2 + > > > > > > include/hw/acpi/aml-build.h | 14 ++- > > > > > > include/hw/acpi/cst.h | 8 ++ > > > > > > include/hw/i386/pc.h | 5 ++ > > > > > > hw/acpi/aml-build.c | 81 ++++++++++++++--- > > > > > > hw/acpi/core.c | 2 +- > > > > > > hw/acpi/cpu.c | 5 ++ > > > > > > hw/acpi/cpu_hotplug.c | 11 +-- > > > > > > hw/acpi/cst.c | 173 > > > > > > ++++++++++++++++++++++++++++++++++++ > > > > > > hw/arm/virt-acpi-build.c | 2 +- > > > > > > hw/i386/acpi-build.c | 10 ++- > > > > > > hw/acpi/Makefile.objs | 2 +- > > > > > > 12 files changed, 290 insertions(+), 25 deletions(-) > > > > > > create mode 100644 include/hw/acpi/cst.h > > > > > > create mode 100644 hw/acpi/cst.c > > > > > > > > > >
