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Re: [Xen-devel] [PATCH v2 8/8] x86/cpuid: Enable CPUID Faulting for the control domain by default
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 13 Sep 2019 15:56:20 +0100
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 13 Sep 2019 14:56:39 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 13/09/2019 07:38, Jan Beulich wrote:
>
>> v2:
>> * Introduce a command line option to retain old behaviour.
>> * Advertise virtualised faulting support to dom0 when it is used.
>>
>> RFC: The previous logic was slightly buggy in that even PVH dom0's had
>> virtualised faulting support hidden from them. Given that this case always
>> hits the CPUID intercept, how much do we care about retaining the old
>> behaviour?
> I'm having trouble with this statement: Neither the description nor
> the actual code change suggest you alter behavior in this regard
> (i.e. with the option used PVH would still be treated the same as
> PV afaict). Yet here you seem to suggest things change with this
> patch.
>
> As to the question, I think I'd consider this a bugfix, and hence
> for the behavior to be okay to change. But as per above I would
> expect the change to init_domain_msr_policy() to also include
> adding is_pv_domain() to the conditional, or alternatively to
> override opt_dom0_cpuid_faulting to true if a PVH Dom0 is being
> built.
I've pulled the bugfix out into an earlier patch so it can be backported.
>> ---
>> xen/arch/x86/cpu/common.c | 59
>> +++++++++++++++++++++++----------------------
>> xen/arch/x86/dom0_build.c | 2 ++
>> xen/arch/x86/msr.c | 3 ++-
>> xen/include/asm-x86/setup.h | 1 +
>> 4 files changed, 35 insertions(+), 30 deletions(-)
> Please also update the command line doc.
Hmm - I wonder where the hunk went... I did write one.
>
>> @@ -92,7 +93,7 @@ int init_domain_msr_policy(struct domain *d)
>> return -ENOMEM;
>>
>> /* See comment in intel_ctxt_switch_levelling() */
>> - if ( is_control_domain(d) )
>> + if ( !opt_dom0_cpuid_faulting && is_control_domain(d) )
>> mp->platform_info.cpuid_faulting = false;
> While unrelated to the overall change here, I think the comment
> would better be updated too, to drop the intel_ prefix of the
> function name.
Fixed in the bugfix patch.
~Andrew
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