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Re: [Xen-devel] [PATCH 1/6] x86/msr: Clean up the MSR_EFER constants


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 28 Jun 2018 14:36:27 +0100
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 28 Jun 2018 13:38:36 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 28/06/18 14:00, Jan Beulich wrote:
>>>> On 26.06.18 at 15:18, <andrew.cooper3@xxxxxxxxxx> wrote:
>> @@ -49,6 +28,18 @@
>>  #define ARCH_CAPS_RSBA                      (_AC(1, ULL) << 2)
>>  #define ARCH_CAPS_SSB_NO            (_AC(1, ULL) << 4)
>>  
>> +#define MSR_EFER                        0xc0000080 /* Extended Feature 
>> Enable Register */
>> +#define EFER_SCE                        (_AC(1, ULL) <<  0) /* SYSCALL 
>> Enable */
>> +#define EFER_LME                        (_AC(1, ULL) <<  8) /* Long Mode 
>> Enable */
>> +#define EFER_LMA                        (_AC(1, ULL) << 10) /* Long Mode 
>> Active */
>> +#define EFER_NXE                        (_AC(1, ULL) << 11) /* No Execute 
>> Enable */
>> +#define EFER_SVME                       (_AC(1, ULL) << 12) /* Secure 
>> Virtual Machine Enable */
>> +#define EFER_LMSLE                      (_AC(1, ULL) << 13) /* Long Mode 
>> Segment Limit Enable */
>> +#define EFER_FFXSE                      (_AC(1, ULL) << 14) /* Fast 
>> FXSAVE/FXRSTOR */
>> +
>> +#define EFER_KNOWN_MASK (EFER_SCE | EFER_LME | EFER_LMA | EFER_NXE | \
>> +                         EFER_SVME | EFER_LMSLE | EFER_FFXSE)
> When meaning to clean up and consolidate these and others, why
> don't we switch to architectural MSR names at the same time? While
> this will increase source size a little, it'll
> - allow grep-ing for the MSRs' uses by their SDM names,
> - significantly reduce the risk of name clashes with something on e.g.
>   the arm side (EFER may not be the most risky one here, but some
>   of the subsequent patches certainly seem to incur such a risk).
>
> I.e. here MSR_IA32_EFER and IA32_EFER_SCE etc.
>
> Other than this I'm certainly fine in general with this cleanup.

Removing IA32 is a deliberate and intended properly.  The
non-architectural vs architectural nature of MSRs changes over time
meaning the names here get stale.

As for grepability, most MSRs can't currently be located like that, and
(naming instability aside) I believe the reduction in code volume is
more important property to have.

There is no chance of clashing with ARM, as these are all arch-specific
constants.  Any common code referencing them should be fixed by becoming
arch-specific code.

As for other clashes, that is always a (slim) risk, but if we encounter
such a problem, we can easily fix the problem there an then.

~Andrew

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