[Xen-devel] [PATCH RFC V2 4/6] xen: Support for VMCALL mem_events

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

Added support for VMCALL events (the memory introspection library
will have the guest trigger VMCALLs, which will then be sent along
via the mem_event mechanism).

Changes since V1:
 - Added a #define and an comment explaining a previous magic
   constant.
 - Had MEM_EVENT_REASON_VMCALL explicitly not honour
   HVMPME_onchangeonly.

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c          |    9 +++++++++
 xen/arch/x86/hvm/vmx/vmx.c      |   18 +++++++++++++++++-
 xen/include/asm-x86/hvm/hvm.h   |    1 +
 xen/include/public/hvm/params.h |    4 +++-
 xen/include/public/mem_event.h  |    5 +++++
 5 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 89a0382..6e86d7c 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -5564,6 +5564,7 @@ long do_hvm_op(unsigned long op, 
XEN_GUEST_HANDLE_PARAM(void) arg)
             case HVM_PARAM_MEMORY_EVENT_INT3:
             case HVM_PARAM_MEMORY_EVENT_SINGLE_STEP:
             case HVM_PARAM_MEMORY_EVENT_MSR:
+            case HVM_PARAM_MEMORY_EVENT_VMCALL:
                 if ( d == current->domain )
                 {
                     rc = -EPERM;
@@ -6199,6 +6200,14 @@ void hvm_memory_event_msr(unsigned long msr, unsigned 
long value)
                            value, ~value, 1, msr);
 }
 
+void hvm_memory_event_vmcall(unsigned long rip, unsigned long eax)
+{
+    hvm_memory_event_traps(current->domain->arch.hvm_domain
+                             .params[HVM_PARAM_MEMORY_EVENT_VMCALL],
+                           MEM_EVENT_REASON_VMCALL,
+                           rip, ~rip, 1, eax);
+}
+
 int hvm_memory_event_int3(unsigned long gla) 
 {
     uint32_t pfec = PFEC_page_present;
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 2caa04a..6c63225 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2879,8 +2879,24 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs)
     case EXIT_REASON_VMCALL:
     {
         int rc;
+        unsigned long eax = regs->eax;
+
         HVMTRACE_1D(VMMCALL, regs->eax);
-        rc = hvm_do_hypercall(regs);
+
+        /* Don't send a VMCALL mem_event unless something
+         * caused the guests's eax register to contain the
+         * VMCALL_EVENT_REQUEST constant. */
+        if ( regs->eax != VMCALL_EVENT_REQUEST )
+        {
+            rc = hvm_do_hypercall(regs);
+        }
+        else
+        {
+            hvm_memory_event_vmcall(guest_cpu_user_regs()->eip, eax);
+            update_guest_eip();
+            break;
+        }
+
         if ( rc != HVM_HCALL_preempted )
         {
             update_guest_eip(); /* Safe: VMCALL */
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 0ebd478..3c0af30 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -475,6 +475,7 @@ void hvm_memory_event_cr0(unsigned long value, unsigned 
long old);
 void hvm_memory_event_cr3(unsigned long value, unsigned long old);
 void hvm_memory_event_cr4(unsigned long value, unsigned long old);
 void hvm_memory_event_msr(unsigned long msr, unsigned long value);
+void hvm_memory_event_vmcall(unsigned long rip, unsigned long eax);
 /* Called for current VCPU on int3: returns -1 if no listener */
 int hvm_memory_event_int3(unsigned long gla);
 
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index 614ff5f..d8f89b5 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -151,6 +151,8 @@
 /* Location of the VM Generation ID in guest physical address space. */
 #define HVM_PARAM_VM_GENERATION_ID_ADDR 34
 
-#define HVM_NR_PARAMS          35
+#define HVM_PARAM_MEMORY_EVENT_VMCALL 35
+
+#define HVM_NR_PARAMS          36
 
 #endif /* __XEN_PUBLIC_HVM_PARAMS_H__ */
diff --git a/xen/include/public/mem_event.h b/xen/include/public/mem_event.h
index b9af728..7a59083 100644
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -47,6 +47,11 @@
 #define MEM_EVENT_REASON_SINGLESTEP  6    /* single step was invoked: gla/gfn 
are RIP */
 #define MEM_EVENT_REASON_MSR         7    /* MSR was hit: gfn is MSR value, 
gla is MSR address;
                                              does NOT honour 
HVMPME_onchangeonly */
+#define MEM_EVENT_REASON_VMCALL      8    /* VMCALL: gfn is RIP, gla is EAX;
+                                             does NOT honour 
HVMPME_onchangeonly */
+
+/* VMCALL mem_events will only be sent when the guest's EAX holds this value. 
*/
+#define VMCALL_EVENT_REQUEST 0x494E5452 /* 'INTR' */
 
 /* Using a custom struct (not hvm_hw_cpu) so as to not fill
  * the mem_event ring buffer too quickly. */
-- 
1.7.9.5


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