Re: [RFC 10/11] x86/mm: Enable CR4.PCIDE on supported systems

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On Tue, Jun 6, 2017 at 2:48 PM, Boris Ostrovsky
<boris.ostrovsky@xxxxxxxxxx> wrote:
> On 06/06/2017 05:35 PM, Andy Lutomirski wrote:
>> On Tue, Jun 6, 2017 at 2:31 PM, Boris Ostrovsky
>> <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>> --- a/arch/x86/xen/setup.c
>>>> +++ b/arch/x86/xen/setup.c
>>>> @@ -1037,6 +1037,12 @@ void __init xen_arch_setup(void)
>>>>       }
>>>>  #endif
>>>>
>>>> +     /*
>>>> +      * Xen would need some work to support PCID: CR3 handling as well
>>>> +      * as xen_flush_tlb_others() would need updating.
>>>> +      */
>>>> +     setup_clear_cpu_cap(X86_FEATURE_PCID);
>>>
>>> Capabilities for PV guests are typically set in xen_init_capabilities() now.
>> Do I need this just for PV or for all Xen guests?  Do the
>> hardware-assisted guests still use paravirt flushes?  Does the
>> hypervisor either support PCID or correctly clear the PCID CPUID bit?
>
>
> For HVM guests Xen will DTRT for CPUID so dealing with PV should be
> sufficient (and xen_arch_setup() is called on PV only anyway)
>
> As far as flushes are concerned for now it's PV only although I believe
> Juergen is thinking about doing this on HVM too.

OK.  I'll move the code to xen_init_capabilities() for the next version.

>
> -boris

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