diff options
Diffstat (limited to 'Documentation/virtual')
| -rw-r--r-- | Documentation/virtual/kvm/mmu.txt | 28 |
1 files changed, 1 insertions, 27 deletions
diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt index 367a952f50ab..f365102c80f5 100644 --- a/Documentation/virtual/kvm/mmu.txt +++ b/Documentation/virtual/kvm/mmu.txt @@ -224,10 +224,6 @@ Shadow pages contain the following information: A bitmap indicating which sptes in spt point (directly or indirectly) at pages that may be unsynchronized. Used to quickly locate all unsychronized pages reachable from a given page. - mmu_valid_gen: - Generation number of the page. It is compared with kvm->arch.mmu_valid_gen - during hash table lookup, and used to skip invalidated shadow pages (see - "Zapping all pages" below.) clear_spte_count: Only present on 32-bit hosts, where a 64-bit spte cannot be written atomically. The reader uses this while running out of the MMU lock @@ -402,27 +398,6 @@ causes its disallow_lpage to be incremented, thus preventing instantiation of a large spte. The frames at the end of an unaligned memory slot have artificially inflated ->disallow_lpages so they can never be instantiated. -Zapping all pages (page generation count) -========================================= - -For the large memory guests, walking and zapping all pages is really slow -(because there are a lot of pages), and also blocks memory accesses of -all VCPUs because it needs to hold the MMU lock. - -To make it be more scalable, kvm maintains a global generation number -which is stored in kvm->arch.mmu_valid_gen. Every shadow page stores -the current global generation-number into sp->mmu_valid_gen when it -is created. Pages with a mismatching generation number are "obsolete". - -When KVM need zap all shadow pages sptes, it just simply increases the global -generation-number then reload root shadow pages on all vcpus. As the VCPUs -create new shadow page tables, the old pages are not used because of the -mismatching generation number. - -KVM then walks through all pages and zaps obsolete pages. While the zap -operation needs to take the MMU lock, the lock can be released periodically -so that the VCPUs can make progress. - Fast invalidation of MMIO sptes =============================== @@ -435,8 +410,7 @@ shadow pages, and is made more scalable with a similar technique. MMIO sptes have a few spare bits, which are used to store a generation number. The global generation number is stored in kvm_memslots(kvm)->generation, and increased whenever guest memory info -changes. This generation number is distinct from the one described in -the previous section. +changes. When KVM finds an MMIO spte, it checks the generation number of the spte. If the generation number of the spte does not equal the global generation |