[Xen-devel] AMD support of hvm_vcpu.single_step

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

Hi AMD folks,

I am unable to see support of single step on amd platform. On intel,
hvm_vcpu.single_step will cause MTF to be set in vmx_intr_assist:

    /* Block event injection when single step with MTF. */
    if ( unlikely(v->arch.hvm_vcpu.single_step) )
    {           
        v->arch.hvm_vmx.exec_control |= CPU_BASED_MONITOR_TRAP_FLAG;
        vmx_update_cpu_exec_control(v);
        return;
    }       

I don't see equivalent on amd? 

Furthermore, as a second issue, in __update_guest_eip(), imo the exception 
is injected into the guest prematurely :

    if ( regs->eflags & X86_EFLAGS_TF )
            hvm_inject_hw_exception(TRAP_debug,
    HVM_DELIVER_NO_ERROR_CODE);

Reason being, in the BP path, __update_guest_eip is called before
domain_pause_for_debugger(). As such, if the BP is handled, there is no
need to inject into the guest. right?

I've the following patch in my tree for the single step issue. LMK what
you think.

thanks
Mukesh


diff --git a/xen/arch/x86/hvm/svm/intr.c b/xen/arch/x86/hvm/svm/intr.c
index 023151a..28d2c6d 100644
--- a/xen/arch/x86/hvm/svm/intr.c
+++ b/xen/arch/x86/hvm/svm/intr.c
@@ -139,6 +139,12 @@ void svm_intr_assist(void)
     struct hvm_intack intack;
     enum hvm_intblk intblk;
 
+    if ( unlikely(v->arch.hvm_vcpu.single_step) )
+    {
+        guest_cpu_user_regs()->eflags |= X86_EFLAGS_TF;
+        return;
+    }
+
     /* Crank the handle on interrupt state. */
     pt_update_irq(v);
 
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index d307dfb..b55825b 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2340,12 +2368,14 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
         break;
 
     case VMEXIT_EXCEPTION_DB:
+        if ( !v->domain->debugger_attached )
+            goto exit_and_crash;
+        else
+            regs->eflags &= ~X86_EFLAGS_TF;
-        if ( !v->domain->debugger_attached )
-            goto exit_and_crash;
         domain_pause_for_debugger();
         break;


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