Re: [PATCH] Setup vcpu add/remove infrastructure, including madt bios_info and dsdt.

[Gleb Natapov <gleb@redhat.com>]

On Fri, Jan 22, 2010 at 10:52:29PM +0800, Liu, Jinsong wrote:
> Gleb Natapov wrote:
> > On Fri, Jan 22, 2010 at 06:54:42PM +0800, Liu, Jinsong wrote:
> >> Gleb Natapov wrote:
> >>> On Fri, Jan 22, 2010 at 05:08:32PM +0800, Liu, Jinsong wrote:
> >>>> Gleb Natapov wrote:
> >>>>> On Fri, Jan 22, 2010 at 10:15:44AM +0800, Liu, Jinsong wrote:
> >>>>>> Gleb Natapov wrote:
> >>>>>>> On Thu, Jan 21, 2010 at 07:48:23PM +0800, Liu, Jinsong wrote:
> >>>>>>>>> From cb997030cba02e7e74a29b3d942aeba9808ed293 Mon Sep 17
> >>>>>>>>> 00:00:00 2001
> >>>>>>>> From: Liu, Jinsong <jinsong.liu@intel.com>
> >>>>>>>> Date: Fri, 22 Jan 2010 03:18:46 +0800
> >>>>>>>> Subject: [PATCH]         Setup vcpu add/remove infrastructure,
> >>>>>>>> including madt bios_info and dsdt.
> >>>>>>>> 
> >>>>>>>>         1. setup madt bios_info structure, so that static dsdt
> >>>>>>>>            get run-time madt info like checksum address, lapic
> >>>>>>>>            address, max cpu numbers, with least hardcode magic
> >>>>>>>>            number (realmode address of bios_info).
> >>>>>>>>         2. setup vcpu add/remove dsdt infrastructure, including
> >>>>>>>>            processor related acpi objects and control methods.
> >>>>>>>>            vcpu add/remove will trigger SCI and then control
> >>>>>>>>            method _L02. By matching madt, vcpu number and
> >>>>>>>>            add/remove action were found, then by notify control
> >>>>>>>> method, it will notify OS acpi driver.
> >>>>>>>> 
> >>>>>>>>         Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
> >>>>>>> It looks like AML code is a port of what we had in BOCHS bios
> >>>>>>> with minor changes. Can you detail what is changed and why for
> >>>>>>> easy review please? And this still doesn't work with Windows I
> >>>>>>> assume. 
> >>>>>>> 
> >>>>>> 
> >>>>>> Yes, my work is based on BOCHS infrastructure, thanks BOCHS :)
> >>>>>> I just change some minor points:
> >>>>>> 1. explicitly define returen value of '_MAT' as 'buffer',
> >>>>>> otherwise some linux acpi driver (i.e. linux 2.6.30) would parse
> >>>>>> error which will handle it as 'integer' not 'buffer';
> >>>>>> 2. keep correct 'checksum' of madt when vcpu add/remove,
> >>>>>> otherwise it will report 'checksum error' when using acpi tools
> >>>>>> to get madt info if we add/remove vcpu; 
> >>>>>> 3. add '_EJ0' so that linux has acpi obj under
> >>>>>> /sys/devices/LNXSYSTM:00, which is need for vcpu remove;
> >>>>>> 4. on Method(PRSC, 0), just scan 'xxx' vcpus that qemu get from
> >>>>>> cmdline para 'maxcpus=xxx', not all 256 vcpus, otherwise under
> >>>>>> some dsdt processor define, it will result error;
> >>>>> What kind of errors? Qemu should never set bit over maxcpus in
> >>>>> PRS. 
> >>>>> 
> >>>> suppose cmdline define vcpus=4, maxvcpus=8
> >>>> in original BOCHS, will scan 15 lapic items start from lapic0 of
> >>>> madt, where it only has maxvcpus lapic items in madt table, hence
> >>>> there is risk to scan over boundary, scan to other acpi table, and
> >>>> result in wrong vcpu online/offline status (in my test, I meet this
> >>>> situation). Because of this reason, this patch limit scan maxvcpus
> >>>> lapic of madt. 
> >>>> 
> >>> But what if cmdline will use vcpu=64? The idea was that \_PR scope
> >>> will reside in its own ssdt and for each maxvcpus value there will
> >>> be ssdt with exactly this number of processors. Ideally ssdt will be
> >>> created dynamically like it is done now, but another solution is to
> >>> create them at bios compilation time and load correct one at
> >>> runtime. 
> >>> 
> >> 
> >> It's OK for vcpu=64. vcpu<maxvcpus.
> >> if maxvcpus > processor defined in dsdt, it's OK since no risk scan
> >> (bios only support 15 processor is another story); if processor
> >> defined in dsdt > maxvcpus, it has risk to scan over boundary. 
> >> 
> >> 
> > Yes, correct. So why not export maxcpus to DSDT and at the beginning
> > of NTFY check that Arg0 < maxcpus then?
> > 
> 
> Yes, your solution also work.
> In fact, we implicitly export maxcpus to DSDT by
> struct bios_info {
>     ...
>     u32 max_cpus_byte;     /* max cpus bitmap bytes */
>     u32 max_cpus_bit;      /* max cpus bitmap bits of last byte */
> };
> this indicate maxvcpus.
> In this way it can reduce scan loop.
> 
Actually your scan loop is twice as big as it was in BOCHS because of
this tricks with bytes and bits.

> However, I think it's not key issue. Both are OK.
> Just different implement way.
> 
The AML code is hard to read as it is, so making it simpler is
important. But the way I want to see this solved in seabios is to create
exactly maxvcpu processors in _PR scope. This will solve MS SVVP problem
too (BOCHS doesn't pass SVVP).

--
			Gleb.