RE: switching from KVM guest to the host .... TLBs not present?

Avi Kivity wrote:
> Zhang, Xiantao wrote:
>> Jes Sorensen wrote:
>> 
>>> Avi Kivity wrote:
>>> 
>>>> Applied, but I note that entering the guest with any lock held is
>>>> problematic, as the guest may spend an arbitrary amount of time in
>>>> guest mode.  Really, entering the guest is almost exactly like
>>>> exiting to userspace. 
>>>> 
>>> Hi Avi,
>>> 
>>> I had a look at this and reworked the locking some, so we don't hold
>>> the slots_lock when entering the guest.
>>> 
>>> How does this look? Xiantao any thoughts of whether it's unsafe to
>>> call kvm_vcpu_post_transition without holding that semaphore? I
>>> believe it should be fine. 
>>> 
>>> I am still seeing issues where the host can get a lock timeout when
>>> running large guests, but the situation seems to be better with
>>> this patch applied. 
>>> 
>> 
>> I remembered this lock should be used to avoid guest memory
>> mappings' changes once vcpu in guest mode before.  Since ia64's
>> memory virtualization locates in VMM, so have to take the lock in
>> VMM, otherwise, guest may access memory with old mapping, but this
>> machanism should be ineffective after optimizing guest's TLB flush
>> in kvm_vcpu_pre_transition.  So this lock shouldn't be held noe.
>> This patch looks fine! Thanks Jes!      
>> 
>> Acked-by : Xiantao Zhang<[email protected]>
>> 
>> But anyway, we should implement kvm_arch_flush_shadow to prevent
>> guest using old mapping to access memory, otherwise guest may have
>> issues even probably crash host once guest memory mapping changes
>> frequently.   
>> 
>> 
> 
> Shouldn't we implement kvm_arch_flush_shadow() before we apply this?

It should be another issue.  Even holding the lock in guest mode, it still have issue.  Okay, anyway I will work out a patch to fix it. 
Xiantao