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Re: [PATCH] xen/x86: Make XEN_DOMCTL_get_vcpu_msrs more configurable
- To: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Wed, 26 Oct 2022 11:05:54 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHY58oHJ6gDkVUXak23gaU3RLT7hK4ghkAA
- Thread-topic: [PATCH] xen/x86: Make XEN_DOMCTL_get_vcpu_msrs more configurable
On 24/10/2022 17:58, Tamas K Lengyel wrote:
> Currently the XEN_DOMCTL_get_vcpu_msrs is only capable of gathering a handful
> of predetermined vcpu MSRs. In our use-case gathering the vPMU MSRs by an
> external privileged tool is necessary, thus we extend the domctl to allow for
> querying for any guest MSRs. To remain compatible with the existing setup if
> no specific MSR is requested via the domctl the default list is returned.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
Naming aside, XEN_DOMCTL_{get,set}_vcpu_msrs is supposed to be "get me
all MSRs needed to migrate a vCPU". (I do intend to retire the
hypercall as part of fixing the Xen side of migration, but that's ages away)
It seems like what you want is something more like
XEN_DOMCTL_{rd,wr}msr_list (convenient timing, given the recent ISE
update). I think those would be better as a separate pair of
hypercalls, rather than trying to repurpose an existing hypercall.
As for actually getting the values, please fix up guest_{rd,wr}msr() to
access the perf MSRs safely. I know the vpmu MSR handling is in a
tragic state, but this new get_msr subop is making the problem even more
tangled.
~Andrew
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