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Re: [Xen-devel] [PATCH v3 04/16] hypervisor part of add vmware_port to xl.cfg

On 09/08/14 11:01, Boris Ostrovsky wrote:
On 09/08/2014 09:15 AM, Don Slutz wrote:
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index b5188e6..12079be 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -59,6 +59,7 @@
  #include <public/sched.h>
  #include <asm/hvm/vpt.h>
  #include <asm/hvm/trace.h>
+#include <asm/hvm/vmport.h>
  #include <asm/hap.h>
  #include <asm/apic.h>
  #include <asm/debugger.h>
@@ -2065,6 +2066,38 @@ svm_vmexit_do_vmsave(struct vmcb_struct *vmcb,
  +static void svm_vmexit_gp_intercept(struct cpu_user_regs *regs,
+                                    struct vcpu *v)
+    struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
+    unsigned long inst_len;
+    unsigned long inst_addr = svm_rip2pointer(v);
+    int rc;
+    static const enum instruction_index list[] = {
+    };
+    regs->error_code = vmcb->exitinfo1;

I am not sure this is a good idea. I have a feeling this may mess up fault reporting in case of double faults (e.g. see AMD volume 2 section 15.2, Example paragraph).

Do you really need to save it into regs or can out pass exitinfo1 as error_code argument directly to vmport_gp_check()?

Nope.  I can pass this on.

+    inst_len = __get_instruction_length_from_list(
+        v, list, ARRAY_SIZE(list), 0);
+ rc = vmport_gp_check(regs, v, inst_len, inst_addr, vmcb->exitinfo2);

You probably want to call this only when __get_instruction_length_from_list() succeeded (i.e. instr_len >0)

This check is inside the vmport_gp_check(). I can extract it to both callers
if that makes sense.

What happens when you have a non-VMware-aware guest that performs this access? Prior to this patch it would get a #GP but now it will continue happily running, right? This changes user-visible behavior.

It depends on the setting of vmware_port. It will still get a #GP if vmware_port is zero. And yes when the config of a guest is changed
to include vmware_port, this changes user-visible behavior.

I wonder whether we should enable #GP intercepts only when we know that the guest is VMware-aware (which we do as far as I can tell since we have a config option).

This may make sense.  The way the code is now, the only change is how
long it takes to get a #GP when vmware_port is zero.

I did some looking into enabling and disabling #GP intercepts but did not
come up with a simple way at the time.  I also thought about it and came
to the conclusion and the number of #GPs that a guest takes which is not
VMware-aware is very few.  So add a lot of complex code seemed to me
to be worse.  I can look at it again.

   -Don Slutz


+    if ( !rc )
+        __update_guest_eip(regs, inst_len);
+    else
+    {
+ "gp: rc=%d e2=%lx ec=%lx ip=%"PRIx64" (%ld) ax=%"PRIx64 + " bx=%"PRIx64" cx=%"PRIx64" dx=%"PRIx64" si=%"PRIx64
+                       " di=%"PRIx64, rc,
+                       (unsigned long)vmcb->exitinfo2,
+                       (unsigned long)regs->error_code,
+ regs->rip, inst_len, regs->rax, regs->rbx, regs->rcx,
+                       regs->rdx, regs->rsi, regs->rdi);
+        hvm_inject_hw_exception(TRAP_gp_fault, regs->error_code);
+    }

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