KVM: Remove unnecessary divide operations

This patch converts unnecessary divide and modulo operations
in the KVM large page related code into logical operations.
This allows to convert gfn_t to u64 while not breaking 32
bit builds.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

2 files changed, 6 insertions, 5 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2bda62485c4c..50c79b9f5c38 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -44,7 +44,8 @@
 
 /* KVM Hugepage definitions for x86 */
 #define KVM_NR_PAGE_SIZES       3
-#define KVM_HPAGE_SHIFT(x)      (PAGE_SHIFT + (((x) - 1) * 9))
+#define KVM_HPAGE_GFN_SHIFT(x)  (((x) - 1) * 9)
+#define KVM_HPAGE_SHIFT(x)      (PAGE_SHIFT + KVM_HPAGE_GFN_SHIFT(x))
 #define KVM_HPAGE_SIZE(x)       (1UL << KVM_HPAGE_SHIFT(x))
 #define KVM_HPAGE_MASK(x)       (~(KVM_HPAGE_SIZE(x) - 1))
 #define KVM_PAGES_PER_HPAGE(x)  (KVM_HPAGE_SIZE(x) / PAGE_SIZE)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index ca07ed083b59..a20fd613acfe 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -423,8 +423,8 @@ static int *slot_largepage_idx(gfn_t gfn,
 {
         unsigned long idx;
 
-        idx = (gfn / KVM_PAGES_PER_HPAGE(level)) -
-              (slot->base_gfn / KVM_PAGES_PER_HPAGE(level));
+        idx = (gfn >> KVM_HPAGE_GFN_SHIFT(level)) -
+              (slot->base_gfn >> KVM_HPAGE_GFN_SHIFT(level));
         return &slot->lpage_info[level - 2][idx].write_count;
 }
 
@@ -528,8 +528,8 @@ static unsigned long *gfn_to_rmap(struct kvm *kvm, gfn_t gfn, int level)
         if (likely(level == PT_PAGE_TABLE_LEVEL))
                 return &slot->rmap[gfn - slot->base_gfn];
 
-        idx = (gfn / KVM_PAGES_PER_HPAGE(level)) -
-                (slot->base_gfn / KVM_PAGES_PER_HPAGE(level));
+        idx = (gfn >> KVM_HPAGE_GFN_SHIFT(level)) -
+                (slot->base_gfn >> KVM_HPAGE_GFN_SHIFT(level));
 
         return &slot->lpage_info[level - 2][idx].rmap_pde;
 }