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Re: [PATCH 1/3] x86/Intel: skip PLATFORM_INFO reads on family 0xf
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Fri, 11 Feb 2022 11:41:36 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Fri, Feb 11, 2022 at 10:59:10AM +0100, Jan Beulich wrote:
> On 11.02.2022 10:40, Roger Pau Monné wrote:
> > On Thu, Feb 10, 2022 at 03:55:52PM +0100, Jan Beulich wrote:
> >> This avoids unnecessary (and always somewhat scary) log messages for the
> >> recovered from #GP(0).
> >
> > Could we maybe get rid of the #GP messages for cases like this where we
> > are explicitly probing for MSR presence? (ie: it's expected that we
> > can get a #GP)
>
> This would mean some form of annotation of such RDMSR attempts (for
> the recovery code to recognize in order to skip the printk()). Not
> all rdmsr_safe() uses are, strictly speaking, probes, so I wouldn't
> want to put such in rdmsr_safe() itself.
>
> In any event - quite a bit more work. Plus I'm not convinced it's a
> good idea to suppress any such log messages.
>
> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >> ---
> >> Perhaps even use "!= 6" in at least the CPUID-faulting family check?
> >
> > Likely, or else you would also need to check for family 11 (Knights
> > Corner?) which doesn't seem to support PLATFORM_INFO either.
>
> I don't think Xen is able to run on these (likewise for IA64, which
> iirc were surfacing as x86 model 7)? These are the co-processor ones,
> aren't they?
Right, Knights Corner uses a socket mount but it's still a
co-processor. It was Knights Landing the first one that could be used
as a host processor.
> My question was more towards whether we would (wrongly)
> exclude future processors when using != 6, if Intel decided to ever
> make new CPUs with a family other than 6.
In the case here I think we should only avoid the probe for family
0xf. Newer families (or even models on family 6 not supporting
PLATFORM_INFO) will just get a #GP message which is OK I think, we
could fix that in due time.
It's better to get a #GP message for probing than to just skip
detection of CPUID faulting on unknown newer families IMO.
Thanks, Roger.
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