Re: [PATCHv4 1/2] x86/ept: invalidate guest physical mappings on VMENTER

[David Vrabel <david.vrabel@citrix.com>]

On 14/12/15 14:52, Andrew Cooper wrote:
> On 14/12/15 14:39, David Vrabel wrote:
>> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
>> index eef0372..6e0cf89 100644
>> --- a/xen/arch/x86/mm/p2m-ept.c
>> +++ b/xen/arch/x86/mm/p2m-ept.c
[...]
>> +    on_selected_cpus(d->domain_dirty_cpumask,
>>                       __ept_sync_domain, p2m, 1);
> 
> You can drop __ept_sync_domain() entirely by using
> smp_send_event_check_mask() instead, which is a no-op IPI (and slightly
> less overhead while holding the IPI lock).

We need to wait until the IPI has been handled on the remote PCPUs since
we may immediately free a page table page.  If a VCPU was still running
it may use paging-structure-cache entries referring to that freed page.

>> -    cpumask_var_t synced_mask;
>> +    cpumask_var_t invalidate;
> 
> Could you include a small comment here to describe the behaviour?  Perhaps:
> 
> /* Whether an INVEPT should be issued on VMENTER? */

Good point.

David