KVM: MMU: Avoid handling same rmap_pde in kvm_handle_hva_range()

When we invalidate a THP page, we call the handler with the same
rmap_pde argument 512 times in the following loop:

  for each guest page in the range
    for each level
      unmap using rmap

This patch avoids these extra handler calls by changing the loop order
like this:

  for each level
    for each rmap in the range
      unmap using rmap

With the preceding patches in the patch series, this made THP page
invalidation more than 5 times faster on our x86 host: the host became
more responsive during swapping the guest's memory as a result.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 18 insertions, 10 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 58adec384489..a5d6ef785b7e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1277,7 +1277,7 @@ static int kvm_handle_hva_range(struct kvm *kvm,
 
         kvm_for_each_memslot(memslot, slots) {
                 unsigned long hva_start, hva_end;
-                gfn_t gfn, gfn_end;
+                gfn_t gfn_start, gfn_end;
 
                 hva_start = max(start, memslot->userspace_addr);
                 hva_end = min(end, memslot->userspace_addr +
@@ -1286,19 +1286,27 @@ static int kvm_handle_hva_range(struct kvm *kvm,
                         continue;
                 /*
                  * {gfn(page) | page intersects with [hva_start, hva_end)} =
-                 * {gfn, gfn+1, ..., gfn_end-1}.
+                 * {gfn_start, gfn_start+1, ..., gfn_end-1}.
                  */
-                gfn = hva_to_gfn_memslot(hva_start, memslot);
+                gfn_start = hva_to_gfn_memslot(hva_start, memslot);
                 gfn_end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, memslot);
 
-                for (; gfn < gfn_end; ++gfn) {
-                        for (j = PT_PAGE_TABLE_LEVEL;
-                             j < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++j) {
-                                unsigned long *rmapp;
+                for (j = PT_PAGE_TABLE_LEVEL;
+                     j < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++j) {
+                        unsigned long idx, idx_end;
+                        unsigned long *rmapp;
 
-                                rmapp = __gfn_to_rmap(gfn, j, memslot);
-                                ret |= handler(kvm, rmapp, memslot, data);
-                        }
+                        /*
+                         * {idx(page_j) | page_j intersects with
+                         *  [hva_start, hva_end)} = {idx, idx+1, ..., idx_end}.
+                         */
+                        idx = gfn_to_index(gfn_start, memslot->base_gfn, j);
+                        idx_end = gfn_to_index(gfn_end - 1, memslot->base_gfn, j);
+
+                        rmapp = __gfn_to_rmap(gfn_start, j, memslot);
+
+                        for (; idx <= idx_end; ++idx)
+                                ret |= handler(kvm, rmapp++, memslot, data);
                 }
         }