KVM: MMU: Clean up the error handling of walk_addr_generic()

Avoid two step jump to the error handling part.  This eliminates the use
of the variables present and rsvd_fault.

We also use the const type qualifier to show that write/user/fetch_fault
do not change in the function.

Both of these were suggested by Ingo Molnar.

Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 32 insertions, 50 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 1caeb4d22e01..f0746d27e33e 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -125,18 +125,17 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
         gfn_t table_gfn;
         unsigned index, pt_access, uninitialized_var(pte_access);
         gpa_t pte_gpa;
-        bool eperm, present, rsvd_fault;
-        int offset, write_fault, user_fault, fetch_fault;
-
-        write_fault = access & PFERR_WRITE_MASK;
-        user_fault = access & PFERR_USER_MASK;
-        fetch_fault = access & PFERR_FETCH_MASK;
+        bool eperm;
+        int offset;
+        const int write_fault = access & PFERR_WRITE_MASK;
+        const int user_fault  = access & PFERR_USER_MASK;
+        const int fetch_fault = access & PFERR_FETCH_MASK;
+        u16 errcode = 0;
 
         trace_kvm_mmu_pagetable_walk(addr, write_fault, user_fault,
                                      fetch_fault);
 walk:
-        present = true;
-        eperm = rsvd_fault = false;
+        eperm = false;
         walker->level = mmu->root_level;
         pte           = mmu->get_cr3(vcpu);
 
@@ -144,10 +143,8 @@ walk:
         if (walker->level == PT32E_ROOT_LEVEL) {
                 pte = kvm_pdptr_read_mmu(vcpu, mmu, (addr >> 30) & 3);
                 trace_kvm_mmu_paging_element(pte, walker->level);
-                if (!is_present_gpte(pte)) {
-                        present = false;
+                if (!is_present_gpte(pte))
                         goto error;
-                }
                 --walker->level;
         }
 #endif
@@ -170,35 +167,27 @@ walk:
 
                 real_gfn = mmu->translate_gpa(vcpu, gfn_to_gpa(table_gfn),
                                               PFERR_USER_MASK|PFERR_WRITE_MASK);
-                if (unlikely(real_gfn == UNMAPPED_GVA)) {
-                        present = false;
-                        break;
-                }
+                if (unlikely(real_gfn == UNMAPPED_GVA))
+                        goto error;
                 real_gfn = gpa_to_gfn(real_gfn);
 
                 host_addr = gfn_to_hva(vcpu->kvm, real_gfn);
-                if (unlikely(kvm_is_error_hva(host_addr))) {
-                        present = false;
-                        break;
-                }
+                if (unlikely(kvm_is_error_hva(host_addr)))
+                        goto error;
 
                 ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
-                if (unlikely(__copy_from_user(&pte, ptep_user, sizeof(pte)))) {
-                        present = false;
-                        break;
-                }
+                if (unlikely(__copy_from_user(&pte, ptep_user, sizeof(pte))))
+                        goto error;
 
                 trace_kvm_mmu_paging_element(pte, walker->level);
 
-                if (unlikely(!is_present_gpte(pte))) {
-                        present = false;
-                        break;
-                }
+                if (unlikely(!is_present_gpte(pte)))
+                        goto error;
 
                 if (unlikely(is_rsvd_bits_set(&vcpu->arch.mmu, pte,
                                               walker->level))) {
-                        rsvd_fault = true;
-                        break;
+                        errcode |= PFERR_RSVD_MASK | PFERR_PRESENT_MASK;
+                        goto error;
                 }
 
                 if (unlikely(write_fault && !is_writable_pte(pte)
@@ -213,17 +202,15 @@ walk:
                         eperm = true;
 #endif
 
-                if (!eperm && !rsvd_fault
-                    && unlikely(!(pte & PT_ACCESSED_MASK))) {
+                if (!eperm && unlikely(!(pte & PT_ACCESSED_MASK))) {
                         int ret;
                         trace_kvm_mmu_set_accessed_bit(table_gfn, index,
                                                        sizeof(pte));
                         ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
                                                   pte, pte|PT_ACCESSED_MASK);
-                        if (unlikely(ret < 0)) {
-                                present = false;
-                                break;
-                        } else if (ret)
+                        if (unlikely(ret < 0))
+                                goto error;
+                        else if (ret)
                                 goto walk;
 
                         mark_page_dirty(vcpu->kvm, table_gfn);
@@ -276,8 +263,10 @@ walk:
                 --walker->level;
         }
 
-        if (unlikely(!present || eperm || rsvd_fault))
+        if (unlikely(eperm)) {
+                errcode |= PFERR_PRESENT_MASK;
                 goto error;
+        }
 
         if (write_fault && unlikely(!is_dirty_gpte(pte))) {
                 int ret;
@@ -285,10 +274,9 @@ walk:
                 trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
                 ret = FNAME(cmpxchg_gpte)(vcpu, mmu, ptep_user, index,
                                           pte, pte|PT_DIRTY_MASK);
-                if (unlikely(ret < 0)) {
-                        present = false;
+                if (unlikely(ret < 0))
                         goto error;
-                } else if (ret)
+                else if (ret)
                         goto walk;
 
                 mark_page_dirty(vcpu->kvm, table_gfn);
@@ -303,20 +291,14 @@ walk:
         return 1;
 
 error:
-        walker->fault.vector = PF_VECTOR;
-        walker->fault.error_code_valid = true;
-        walker->fault.error_code = 0;
-        if (present)
-                walker->fault.error_code |= PFERR_PRESENT_MASK;
-
-        walker->fault.error_code |= write_fault | user_fault;
-
+        errcode |= write_fault | user_fault;
         if (fetch_fault && (mmu->nx ||
                             kvm_read_cr4_bits(vcpu, X86_CR4_SMEP)))
-                walker->fault.error_code |= PFERR_FETCH_MASK;
-        if (rsvd_fault)
-                walker->fault.error_code |= PFERR_RSVD_MASK;
+                errcode |= PFERR_FETCH_MASK;
 
+        walker->fault.vector = PF_VECTOR;
+        walker->fault.error_code_valid = true;
+        walker->fault.error_code = errcode;
         walker->fault.address = addr;
         walker->fault.nested_page_fault = mmu != vcpu->arch.walk_mmu;