Re: [PATCH 5/9] [VMX] Do not re-execute INTn instruction.

[Avi Kivity <avi@redhat.com>]

Gleb Natapov wrote:
>>> +	u8 event_exit_inst_len;
>>> +
>>>       
>> Can we simply read the field when we need, instead of a new field?
>>
>>     
> Usually relying on vm exit information to be valid before vm entry
> is wrong because migration can happen in a meantime. In this particular
> case it is not so obvious since we don't want to migrate pending soft
> interrupt, but re-execute instruction instead (we could migrate it
> theoretically and may be we should, but when migrating from AMD to
> Intel we don't have this info anyway). Another case where instruction
> length as read from vmx may be outdated at interrupt injection time is
> if exception happened during interrupt delivery and exception should be
> re-injected first.
>   

Note that in some cases we do keep things in vmcs/vmcb fields -- the 
registers, segments, etc.  This is because we have per-vendor accessors 
for them, so we maintain a "virtual data structure" that common code can 
access.

We could do something similar with the interrupt queue - keep part of it 
in the vmcs/vmcb and use accessors to modify it.  But I don't think it's 
worthwhile; for vmx we have to read and write it anyway (since, unlike 
the registers, the exit and entry fields are different) and for svm it's 
in memory anyway so reading and writing it back is very cheap.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.