Re: [PATCH v2 05/10] KVM: x86: interrupt based APF 'page ready' event delivery

[Paolo Bonzini]

On 09/06/20 21:10, Vivek Goyal wrote:
> Hi Vitaly,
> 
> Have a question about page ready events. 
> 
> Now we deliver PAGE_NOT_PRESENT page faults only if guest is not in
> kernel mode. So say kernel tried to access a page and we halted cpu.
> When page is available, we will inject page_ready interrupt. At
> that time we don't seem to check whether page_not_present was injected
> or not. 
> 
> IOW, we seem to deliver page_ready irrespective of the fact whether
> PAGE_NOT_PRESENT was delivered or not. And that means we will be
> sending page present tokens to guest. Guest will not have a state
> associated with that token and think that page_not_present has
> not been delivered yet and allocate an element in hash table for
> future page_not_present event. And that will lead to memory leak
> and token conflict etc.

Yes, and this is https://bugzilla.kernel.org/show_bug.cgi?id=208081
which I was looking at right today.

> While setting up async pf, should we keep track whether associated
> page_not_present was delivered to guest or not and deliver page_ready
> accordingly.

Yes, I think so.

Paolo