summaryrefslogtreecommitdiff
path: root/Documentation/virtual
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/virtual')
-rw-r--r--Documentation/virtual/kvm/mmu.txt28
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