On Fri, Aug 5, 2011 at 2:08 AM, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: > On 2011-08-05 10:40, Cyclonus J wrote: >> On Fri, Aug 5, 2011 at 12:41 AM, Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: >>> On 2011-08-05 09:20, Cyclonus J wrote: >>>> hi, >>>> >>>> I am wondering if it is possible to map guest MMIO to host MMIO, the >>>> purpose is to reduce VM_EXIT as the page tables will be setup before >>>> MMIO accessing from guest. Here is what I have in mind: >>> >>> This is already the case if you pass through devices AND aligment&size >>> of the MMIO resource allows this. >> >> I assume here pass through means using VT-d? > > ...or AMD IOMMU. Yes. > >> Unfortunately, I can't >> use it for my case and I need to para-virtualize guest OS as well. > > Even with PV, you can't avoid VM exits if the IO access has side > effects, ie. is supposed to trigger some device activity. Or if it is > backed by some logic. > > You can only avoid exits if MMIO behaves like RAM. But then it's better > to use RAM directly, like virtio but also real devices do for request data. > > Again my question what device you want to optimize precisely. This is for graphic card. Currently, every MMIO access with take a VM_EXIT which is too expensive I think. CJ > > Jan > > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
