Re: [PATCH v2] KVM: VMX: Update instruction length on intercepted BP

[Jan Kiszka <jan.kiszka@siemens.com>]

Gleb Natapov wrote:
> On Wed, Feb 17, 2010 at 01:13:29PM +0200, Avi Kivity wrote:
>> On 02/17/2010 12:43 PM, Gleb Natapov wrote:
>>>> And, again: This is an _existing_ user space ABI. We could only provide
>>>> an alternative, but we have to maintain what is there at least for some
>>>> longer grace period.
>>>>
>>> But it was always broken for SVM and was broken for VMX for a year and
>>> nobody noticed, so may be instead of reintroducing old interface we should
>>> do it right this time?
>> We need to fix the existing interface first, and then think long and
>> hard if we want yet another interface, since we're likely to screw
>> it up as well.
>>
>> The more interfaces we introduce, the harder maintenance becomes.
>>
> We are in a sad state if we cannot improve interface. The current one
> outsource part of CPU functionality into userspace. This should be a big
> no-no.

I still disagree on this. Moving the decision logic to user space
prevented to re-implement a gdbstub in kernel space. I oversaw that
re-injecting #BP over older SVM was broken, but it is now fixed for all
vendors. So moving it back to kernel has actually no long-term reason.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux