Re: [Xen-devel] [PATCH 1/5] xen/vm_event: Added support for XSETBV events

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/05/15 10:06, Razvan Cojocaru wrote:
> On 05/07/2015 09:03 PM, Andrew Cooper wrote:
>> In an effort to be architecture neutral, it might be an idea to have
>> something like
>>
>> struct vm_event_write_cr {
>>     uint64_t index;
>>     uint64_t old_val, new_val;
>> };
>>
>> And have a per-arch index of control registers, such as
>>
>> X86_CR0
>> X86_CR3
>> X86_CR4
>> X86_XCR0
>> ...
>> ARM32_$foo
> Staging's vm_event.h looks like this now:
>
>  63 /* CR0 was updated */
>  64 #define VM_EVENT_REASON_MOV_TO_CR0              4
>  65 /* CR3 was updated */
>  66 #define VM_EVENT_REASON_MOV_TO_CR3              5
>  67 /* CR4 was updated */
>  68 #define VM_EVENT_REASON_MOV_TO_CR4              6
>  69 /* An MSR was updated. */
>  70 #define VM_EVENT_REASON_MOV_TO_MSR              7
>
> Now, I can change VM_EVENT_REASON_MOV_TO_CR0 to
> VM_EVENT_REASON_MOV_TO_CR and use that for all CR and XCR events (well,
> only XCR0 now).
>
> Should VM_EVENT_REASON_MOV_TO_MSR become 5, or should we keep backward
> compatibility with prior clients and leave a gap?

For Tamas' cleanup series, we accepted ABI/API incompatible changes to
try and get the interface in order.  Therefore, until 4.6 is released,
anything goes, and I am very much in favour of more changes to clean the
arch-specific bits out of the common bits.

~Andrew

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