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 <[email protected]> Signed-off-by: Marcelo Tosatti <[email protected]>
chewitt · Aug 1, 2010 · 8285541 · 8285541
1 parent 95c87e2
commit 8285541
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Showing 6 changed files with 15 additions and 11 deletions.
diff --git a/arch/ia64/include/asm/kvm_host.h b/arch/ia64/include/asm/kvm_host.h
@@ -235,6 +235,7 @@ struct kvm_vm_data {
 #define KVM_REQ_PTC_G		32
 #define KVM_REQ_RESUME		33
 
+#define KVM_HPAGE_GFN_SHIFT(x)	0
 #define KVM_NR_PAGE_SIZES	1
 #define KVM_PAGES_PER_HPAGE(x)	1
 

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
@@ -35,6 +35,7 @@
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
 
 /* We don't currently support large pages. */
+#define KVM_HPAGE_GFN_SHIFT(x)	0
 #define KVM_NR_PAGE_SIZES	1
 #define KVM_PAGES_PER_HPAGE(x)	(1UL<<31)
 

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
@@ -41,7 +41,8 @@ struct sca_block {
 } __attribute__((packed));
 
 #define KVM_NR_PAGE_SIZES 2
-#define KVM_HPAGE_SHIFT(x) (PAGE_SHIFT + ((x) - 1) * 8)
+#define KVM_HPAGE_GFN_SHIFT(x) (((x) - 1) * 8)
+#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/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
@@ -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;
 }

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
@@ -626,9 +626,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		if (new.lpage_info[i])
 			continue;
 
-		lpages = 1 + (base_gfn + npages - 1) /
-			     KVM_PAGES_PER_HPAGE(level);
-		lpages -= base_gfn / KVM_PAGES_PER_HPAGE(level);
+		lpages = 1 + ((base_gfn + npages - 1)
+			     >> KVM_HPAGE_GFN_SHIFT(level));
+		lpages -= base_gfn >> KVM_HPAGE_GFN_SHIFT(level);
 
 		new.lpage_info[i] = vmalloc(lpages * sizeof(*new.lpage_info[i]));
 
@@ -638,9 +638,9 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		memset(new.lpage_info[i], 0,
 		       lpages * sizeof(*new.lpage_info[i]));
 
-		if (base_gfn % KVM_PAGES_PER_HPAGE(level))
+		if (base_gfn & (KVM_PAGES_PER_HPAGE(level) - 1))
 			new.lpage_info[i][0].write_count = 1;
-		if ((base_gfn+npages) % KVM_PAGES_PER_HPAGE(level))
+		if ((base_gfn+npages) & (KVM_PAGES_PER_HPAGE(level) - 1))
 			new.lpage_info[i][lpages - 1].write_count = 1;
 		ugfn = new.userspace_addr >> PAGE_SHIFT;
 		/*