x86/HVM: prevent infinite VM entry retries

This reverts the VMX side of commit 28b4baac ("x86/HVM: don't crash
guest upon problems occurring in user mode") and gets SVM in line with
the resulting VMX behavior. This is because Andrew validly says

"A failed vmentry is overwhelmingly likely to be caused by corrupt
 VMC[SB] state.  As a result, injecting a fault and retrying the the
 vmentry is likely to fail in the same way."

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Tim Deegan <tim@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 939869015a8d240e8ee785f12da100df6dd2ff91..a7655bdb8e05aa4b9f8d2aa56c7b2cf30a32629a 100644 (file)
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2371,8 +2371,8 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
                 goto out;
             case NESTEDHVM_VMEXIT_FATALERROR:
                 gdprintk(XENLOG_ERR, "unexpected nestedsvm_vmexit() error\n");
-                goto exit_and_crash;
-
+                domain_crash(v->domain);
+                goto out;
             default:
                 BUG();
             case NESTEDHVM_VMEXIT_ERROR:
@@ -2385,18 +2385,22 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
         case NESTEDHVM_VMEXIT_FATALERROR:
             gdprintk(XENLOG_ERR,
                 "unexpected nestedsvm_check_intercepts() error\n");
-            goto exit_and_crash;
+            domain_crash(v->domain);
+            goto out;
         default:
             gdprintk(XENLOG_INFO, "nestedsvm_check_intercepts() returned %i\n",
                 nsret);
-            goto exit_and_crash;
+            domain_crash(v->domain);
+            goto out;
         }
     }
 
     if ( unlikely(exit_reason == VMEXIT_INVALID) )
     {
+        gdprintk(XENLOG_ERR, "invalid VMCB state:\n");
         svm_vmcb_dump(__func__, vmcb);
-        goto exit_and_crash;
+        domain_crash(v->domain);
+        goto out;
     }
 
     perfc_incra(svmexits, exit_reason);
@@ -2431,13 +2435,13 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
 
     case VMEXIT_EXCEPTION_DB:
         if ( !v->domain->debugger_attached )
-            goto exit_and_crash;
+            goto unexpected_exit_type;
         domain_pause_for_debugger();
         break;
 
     case VMEXIT_EXCEPTION_BP:
         if ( !v->domain->debugger_attached )
-            goto exit_and_crash;
+            goto unexpected_exit_type;
         /* AMD Vol2, 15.11: INT3, INTO, BOUND intercepts do not update RIP. */
         if ( (inst_len = __get_instruction_length(v, INSTR_INT3)) == 0 )
             break;
@@ -2684,7 +2688,7 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
         break;
 
     default:
-    exit_and_crash:
+    unexpected_exit_type:
         gdprintk(XENLOG_ERR, "unexpected VMEXIT: exit reason = %#"PRIx64", "
                  "exitinfo1 = %#"PRIx64", exitinfo2 = %#"PRIx64"\n",
                  exit_reason, 

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 2907afa408a1fef04d8ccdcc9918a9b026942c36..0bf92b25c2435913b828e880e1c30a6a0acc8b4d 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -134,18 +134,6 @@ static void vmx_vcpu_destroy(struct vcpu *v)
     passive_domain_destroy(v);
 }
 
-/* Only crash the guest if the problem originates in kernel mode. */
-static void vmx_crash_or_fault(struct vcpu *v)
-{
-    struct segment_register ss;
-
-    vmx_get_segment_register(v, x86_seg_ss, &ss);
-    if ( ss.attr.fields.dpl )
-        hvm_inject_hw_exception(TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE);
-    else
-        domain_crash(v->domain);
-}
-
 static DEFINE_PER_CPU(struct vmx_msr_state, host_msr_state);
 
 static const u32 msr_index[] =
@@ -2520,7 +2508,7 @@ static void vmx_failed_vmentry(unsigned int exit_reason,
     vmcs_dump_vcpu(curr);
     printk("**************************************\n");
 
-    vmx_crash_or_fault(curr);
+    domain_crash(curr->domain);
 }
 
 void vmx_enter_realmode(struct cpu_user_regs *regs)
@@ -3173,8 +3161,19 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
     /* fall through */
     default:
     exit_and_crash:
-        gdprintk(XENLOG_WARNING, "Bad vmexit (reason %#lx)\n", exit_reason);
-        vmx_crash_or_fault(v);
+        {
+            struct segment_register ss;
+
+            gdprintk(XENLOG_WARNING, "Bad vmexit (reason %#lx)\n",
+                     exit_reason);
+
+            vmx_get_segment_register(v, x86_seg_ss, &ss);
+            if ( ss.attr.fields.dpl )
+                hvm_inject_hw_exception(TRAP_invalid_op,
+                                        HVM_DELIVER_NO_ERROR_CODE);
+            else
+                domain_crash(v->domain);
+        }
         break;
     }