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[Xen-devel] [ping] Re: [PATCH 2/5] x86/pv: Avoid leaking other guests' MSR_TSC_AUX values into PV context

On 26/02/18 11:25, Jan Beulich wrote:
>>>> On 20.02.18 at 12:58, <andrew.cooper3@xxxxxxxxxx> wrote:
>> If the CPU pipeline supports RDTSCP or RDPID, a guest can observe the value 
>> in
>> MSR_TSC_AUX, irrespective of whether the relevant CPUID features are
>> advertised/hidden.
>> At the moment, paravirt_ctxt_switch_to() only writes to MSR_TSC_AUX if
>> TSC_MODE_PVRDTSCP mode is enabled, but this is not the default mode.
>> Therefore, default PV guests can read the value from a previously scheduled
>> HVM vcpu, or TSC_MODE_PVRDTSCP-enabled PV guest.
>> Alter the PV path to always write to MSR_TSC_AUX, using 0 in the common 
>> case.
>> To amortise overhead cost, introduce wrmsr_tsc_aux() which performs a lazy
>> update of the MSR, and use this function consistently across the codebase.
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Despite me continuing to think that RDTSCP and RDPID should be
> fully independent features, this being in line with the SDM:
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>


Given the important of this patch, I feel it is time to ping the VT-x
and SVM maintainers for their input.


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