Re: [Xen-devel] pvops microcode support for AMD FAM >= 15

[Ian Campbell <ijc@xxxxxxxxxxxxxx>]

On Wed, 2012-12-05 at 16:48 +0000, Boris Ostrovsky wrote:
> On 12/05/2012 07:43 AM, Ian Campbell wrote:
> > I've just tried this on a fam 15h and I get:
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000626
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: CPU0 found a matching microcode update with 
> > version 0x6000629 (current=0x6000626)
> >          (XEN) microcode: CPU0 updated from revision 0x6000626 to 0x6000629
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000629
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: size 5260, block size 2592, offset 2660
> >          (XEN) microcode: CPU1 patch does not match (patch is 6101, cpu 
> > base id is 6012)
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000626
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: CPU2 found a matching microcode update with 
> > version 0x6000629 (current=0x6000626)
> >          (XEN) microcode: CPU2 updated from revision 0x6000626 to 0x6000629
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000629
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: size 5260, block size 2592, offset 2660
> >          (XEN) microcode: CPU3 patch does not match (patch is 6101, cpu 
> > base id is 6012)
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000626
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: CPU4 found a matching microcode update with 
> > version 0x6000629 (current=0x6000626)
> >          (XEN) microcode: CPU4 updated from revision 0x6000626 to 0x6000629
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000629
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: size 5260, block size 2592, offset 2660
> >          (XEN) microcode: CPU5 patch does not match (patch is 6101, cpu 
> > base id is 6012)
> >
> >          (XEN) microcode: collect_cpu_info: patch_id=0x6000626
> >          (XEN) microcode: size 5260, block size 2592, offset 60
> >          (XEN) microcode: CPU6 found a matching microcode update with 
> > version 0x6000629 (current=0x6000626)
> >          (XEN) microcode: CPU6 updated from revision 0x6000626 to 0x6000629
> >
> >          ....
> >
> > It seems like it is applying successfully on only the even numbered
> > cpus. Is this because the odd and even ones share some execution units
> > and therefore share microcode updates too? IOW update CPU0 also updates
> > CPU1 under the hood.
> >
> > If so then we probably want to teach Xen about this, although at least
> > for now though it would mean that the microcode is actually getting
> > applied despite the messages.
> 
> On fam15h cores are grouped in pairs into compute units (CUs) and cores 
> in CUs share microcode engine. So yes, you are right --- when we apply a 
> patch to one core, the other one sees the update.
> 
> I believe at some point we thought about making code smarter and 
> applying patch only on one core in a CU but then decided against it 
> because of some corner cases, For example, there are parts with 
> single-core CUs and it is not out of question that some BIOSes may not 
> enumerate them correctly. Yes, we can figure this all out in the code 
> but we didn't feel that adding complexity was worth it.

It looks to me like Linux silently avoids updating the microcode on a
core if it detects that already has that version, which silently avoids
this issue without the possibility of missing a core out in a corned
case.

I looked at trying to apply the same logic to the Xen side of things but
it is different enough that I can't immediately see how.
microcode_fits() would seem to be the place to do it, but I'm not at all
sure what this equiv table stuff is all about.

Ian.

-- 
Ian Campbell

I've finally found the perfect girl,
I couldn't ask for more,
She's deaf and dumb and over-sexed,
And owns a liquor store.


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