KVM: MMU: Make pte_list_desc fit cache lines well

We have PTE_LIST_EXT + 1 pointers in this structure and these 40/20
bytes do not fit cache lines well.  Furthermore, some allocators may
use 64/32-byte objects for the pte_list_desc cache.

This patch solves this problem by changing PTE_LIST_EXT from 4 to 3.

For shadow paging, the new size is still large enough to hold both the
kernel and process mappings for usual anonymous pages.  For file
mappings, there may be a slight change in the cache usage.

Note: with EPT/NPT we almost always have a single spte in each reverse
mapping and we will not see any change by this.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index dc5f2459db6c..3213348e3a93 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -135,8 +135,6 @@ module_param(dbg, bool, 0644);
 #define PT64_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | PT_USER_MASK \
                         | PT64_NX_MASK)
 
-#define PTE_LIST_EXT 4
-
 #define ACC_EXEC_MASK    1
 #define ACC_WRITE_MASK   PT_WRITABLE_MASK
 #define ACC_USER_MASK    PT_USER_MASK
@@ -151,6 +149,9 @@ module_param(dbg, bool, 0644);
 
 #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level)
 
+/* make pte_list_desc fit well in cache line */
+#define PTE_LIST_EXT 3
+
 struct pte_list_desc {
         u64 *sptes[PTE_LIST_EXT];
         struct pte_list_desc *more;