CCing Marcelo, On Wed, Jun 18, 2014 at 02:50:44PM +0800, Tang Chen wrote: > Hi Gleb, > > Thanks for the quick reply. Please see below. > > On 06/18/2014 02:12 PM, Gleb Natapov wrote: > >On Wed, Jun 18, 2014 at 01:50:00PM +0800, Tang Chen wrote: > >>[Questions] > >>And by the way, would you guys please answer the following questions for me ? > >> > >>1. What's the ept identity pagetable for ? Only one page is enough ? > >> > >>2. Is the ept identity pagetable only used in realmode ? > >> Can we free it once the guest is up (vcpu in protect mode)? > >> > >>3. Now, ept identity pagetable is allocated in qemu userspace. > >> Can we allocate it in kernel space ? > >What would be the benefit? > > I think the benefit is we can hot-remove the host memory a kvm guest > is using. > > For now, only memory in ZONE_MOVABLE can be migrated/hot-removed. And the > kernel > will never use ZONE_MOVABLE memory. So if we can allocate these two pages in > kernel space, we can pin them without any trouble. When doing memory > hot-remove, > the kernel will not try to migrate these two pages. But we can do that by other means, no? The patch you've sent for instance. > > > > >> > >>4. If I want to migrate these two pages, what do you think is the best way ? > >> > >I answered most of those here: http://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg103718.html > > I'm sorry I must missed this email. > > Seeing your advice, we can unpin these two pages and repin them in the next > EPT violation. > So about this problem, which solution would you prefer, allocate these two > pages in kernel > space, or migrate them before memory hot-remove ? > > I think the first solution is simpler. But I'm not quite sure if there is > any other pages > pinned in memory. If we have the same problem with other kvm pages, I think > it is better to > solve it in the second way. > > What do you think ? Remove pinning is preferable. In fact looks like for identity pagetable it should be trivial, just don't pin. APIC access page is a little bit more complicated since its physical address needs to be tracked to be updated in VMCS. -- Gleb. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>