On Thu, 04 Jan 2007 17:48:45 +0200 Avi Kivity <[EMAIL PROTECTED]> wrote:
> The current kvm shadow page table implementation does not cache shadow > page tables (except for global translations, used for kernel addresses) > across context switches. This means that after a context switch, every > memory access will trap into the host. After a while, the shadow page > tables will be rebuild, and the guest can proceed at native speed until > the next context switch. > > The natural solution, then, is to cache shadow page tables across > context switches. Unfortunately, this introduces a bucketload of problems: > > - the guest does not notify the processor (and hence kvm) that it > modifies a page table entry if it has reason to believe that the > modification will be followed by a tlb flush. It becomes necessary to > write-protect guest page tables so that we can use the page fault when > the access occurs as a notification. > - write protecting the guest page tables means we need to keep track of > which ptes map those guest page table. We need to add reverse mapping > for all mapped writable guest pages. > - when the guest does access the write-protected page, we need to allow > it to perform the write in some way. We do that either by emulating the > write, or removing all shadow page tables for that page and allowing the > write to proceed, depending on circumstances. > > This patchset implements the ideas above. While a lot of tuning remains > to be done (for example, a sane page replacement algorithm), a guest > running with this patchset applied is much faster and more responsive > than with 2.6.20-rc3. Some preliminary benchmarks are available in > http://article.gmane.org/gmane.comp.emulators.kvm.devel/661. > > The patchset is bisectable compile-wise. Is this intended for 2.6.20, or would you prefer that we release what we have now and hold this off for 2.6.21? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/