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Re: [PATCH RFC 0/9] x86: Merge cpuid and msr policy
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 30 Mar 2023 13:07:29 +0200
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Thu, 30 Mar 2023 11:08:27 +0000
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On Wed, Mar 29, 2023 at 09:51:28PM +0100, Andrew Cooper wrote:
> tl;dr to add MSR_ARCH_CAPS features sensibly, cpu_{featureset<->policy}() need
> to not operate on objects of differing lifetimes, so structs
> {cpuid,msr}_policy need merging and cpu_policy is the obvious name.
So the problem is that there's a chance we might get a cpu_policy
object that contains a valid (allocated) cpuid object, but not an msr
one?
Or the problem is rather with the domain struct containing separate
cpuid/msr fields not encapsulated in the cpu_policy struct?
I don't think the current set of cpu_policy operations permit you to
operate on incomplete objects anyway.
I assume you are worried about the usage of x86_msr_copy_from_buffer()
for example that could load data into the MSR_ARCH_CAPS field for the
msr object without checking that the corresponding CPUID bit is set?
> But this does mean that we now have
>
> cpu_policy->basic.$X
> cpu_policy->feat.$Y
> cpu_policy->arch_caps.$Z
I'm not sure I like the fact that we now can't differentiate between
policy fields related to MSRs or CPUID leafs.
Isn't there a chance we might in the future get some name space
collision by us having decided to unify both?
Thanks, Roger.
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