KVM: PPC: Reduce calls to get current->mm by storing the value locally

Reduces the number of calls to get_current() in order to get the value of
current->mm by doing it once and storing the value, since it is not
supposed to change inside the same process).
Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -508,6 +508,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	struct vm_area_struct *vma;
 	unsigned long rcbits;
 	long mmio_update;
+	struct mm_struct *mm;
 
 	if (kvm_is_radix(kvm))
 		return kvmppc_book3s_radix_page_fault(run, vcpu, ea, dsisr);
@@ -584,6 +585,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	is_ci = false;
 	pfn = 0;
 	page = NULL;
+	mm = current->mm;
 	pte_size = PAGE_SIZE;
 	writing = (dsisr & DSISR_ISSTORE) != 0;
 	/* If writing != 0, then the HPTE must allow writing, if we get here */
@@ -592,8 +594,8 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	npages = get_user_pages_fast(hva, 1, writing ? FOLL_WRITE : 0, pages);
 	if (npages < 1) {
 		/* Check if it's an I/O mapping */
-		down_read(&current->mm->mmap_sem);
-		vma = find_vma(current->mm, hva);
+		down_read(&mm->mmap_sem);
+		vma = find_vma(mm, hva);
 		if (vma && vma->vm_start <= hva && hva + psize <= vma->vm_end &&
 		    (vma->vm_flags & VM_PFNMAP)) {
 			pfn = vma->vm_pgoff +
@@ -602,7 +604,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			is_ci = pte_ci(__pte((pgprot_val(vma->vm_page_prot))));
 			write_ok = vma->vm_flags & VM_WRITE;
 		}
-		up_read(&current->mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 		if (!pfn)
 			goto out_put;
 	} else {
@@ -621,8 +623,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			 * hugepage split and collapse.
 			 */
 			local_irq_save(flags);
-			ptep = find_current_mm_pte(current->mm->pgd,
-						   hva, NULL, NULL);
+			ptep = find_current_mm_pte(mm->pgd, hva, NULL, NULL);
 			if (ptep) {
 				pte = kvmppc_read_update_linux_pte(ptep, 1);
 				if (__pte_write(pte))