Re: [Xen-devel] [PATCH v1 4/5] x86/msr: introduce guest_rdmsr()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 30/08/17 11:34, Sergey Dyasli wrote:
> The new function is responsible for handling RDMSR from both HVM and PV
> guests. Currently it handles only 2 MSRs:
>
>     MSR_INTEL_PLATFORM_INFO
>     MSR_INTEL_MISC_FEATURES_ENABLES
>
> It has a different behaviour compared to the old MSR handlers: if MSR
> is being handled by guest_rdmsr() then RDMSR will either succeed (if
> a guest is allowed to access it based on its MSR policy) or produce
> a GP fault. A guest will never see a H/W value of some MSR unknown to
> this function.
>
> guest_rdmsr() unifies and replaces the handling code from
> vmx_msr_read_intercept() and priv_op_read_msr().
>
> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>

You should also note that this (along with the prep work in
init_domain_msr_policy()) fixes a bug where dom0 could probe and find
CPUID faulting, even though it couldn't actually use it.

~Andrew

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