[Xen-devel] [PATCH V3 1/2] xen, libxc: Fine grained control of REP emulation optimizations

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

Previously, if vm_event emulation support was enabled, then REP
optimizations were disabled when emulating REP-compatible
instructions. This patch allows fine-tuning of this behaviour by
providing a dedicated libxc helper function.

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

---
Changes since V2:
 - Now only checking ->arch.mem_access_emulate_each_rep in
   hvmemul_virtual_to_linear() (previously was also checking
   ->arch.mem_access_emulate_enabled.
 - Disabling ->arch.mem_access_emulate_enabled when monitoring
   is disabled.
 - Changed the if()s in vm_event_resume() to a switch().
 - Added Ian Campbell's ack.
---
 tools/libxc/include/xenctrl.h |   12 ++++++++++++
 tools/libxc/xc_monitor.c      |   13 +++++++++++++
 xen/arch/x86/hvm/emulate.c    |    2 +-
 xen/arch/x86/monitor.c        |    7 ++++++-
 xen/arch/x86/vm_event.c       |    2 ++
 xen/include/asm-x86/domain.h  |    1 +
 xen/include/public/domctl.h   |    1 +
 7 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 3482544..3bfa00b 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -2428,6 +2428,18 @@ int xc_monitor_software_breakpoint(xc_interface *xch, 
domid_t domain_id,
 int xc_monitor_guest_request(xc_interface *xch, domid_t domain_id,
                              bool enable, bool sync);
 
+/**
+ * This function enables / disables emulation for each REP for a
+ * REP-compatible instruction.
+ *
+ * @parm xch a handle to an open hypervisor interface.
+ * @parm domain_id the domain id one wants to get the node affinity of.
+ * @parm enable if 0 optimize when possible, else emulate each REP.
+ * @return 0 on success, -1 on failure.
+ */
+int xc_monitor_emulate_each_rep(xc_interface *xch, domid_t domain_id,
+                                bool enable);
+
 /***
  * Memory sharing operations.
  *
diff --git a/tools/libxc/xc_monitor.c b/tools/libxc/xc_monitor.c
index 065669c..b1705dd 100644
--- a/tools/libxc/xc_monitor.c
+++ b/tools/libxc/xc_monitor.c
@@ -143,3 +143,16 @@ int xc_monitor_guest_request(xc_interface *xch, domid_t 
domain_id, bool enable,
 
     return do_domctl(xch, &domctl);
 }
+
+int xc_monitor_emulate_each_rep(xc_interface *xch, domid_t domain_id,
+                                bool enable)
+{
+    DECLARE_DOMCTL;
+
+    domctl.cmd = XEN_DOMCTL_monitor_op;
+    domctl.domain = domain_id;
+    domctl.u.monitor_op.op = XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP;
+    domctl.u.monitor_op.event = enable;
+
+    return do_domctl(xch, &domctl);
+}
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 5934c72..39774b7 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -514,7 +514,7 @@ static int hvmemul_virtual_to_linear(
      * being triggered for repeated writes to a whole page.
      */
     *reps = min_t(unsigned long, *reps,
-                  unlikely(current->domain->arch.mem_access_emulate_enabled)
+                  unlikely(current->domain->arch.mem_access_emulate_each_rep)
                            ? 1 : 4096);
 
     reg = hvmemul_get_seg_reg(seg, hvmemul_ctxt);
diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
index 3d52135..7611f7b 100644
--- a/xen/arch/x86/monitor.c
+++ b/xen/arch/x86/monitor.c
@@ -73,10 +73,15 @@ int monitor_domctl(struct domain *d, struct 
xen_domctl_monitor_op *mop)
     if ( rc )
         return rc;
 
-    if ( mop->op == XEN_DOMCTL_MONITOR_OP_GET_CAPABILITIES )
+    switch ( mop->op )
     {
+    case XEN_DOMCTL_MONITOR_OP_GET_CAPABILITIES:
         mop->event = capabilities;
         return 0;
+
+    case XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP:
+        d->arch.mem_access_emulate_each_rep = !!mop->event;
+        return 0;
     }
 
     /*
diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index e4e0aa4..c38d37b 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -54,6 +54,8 @@ void vm_event_cleanup_domain(struct domain *d)
         xfree(v->arch.vm_event);
         v->arch.vm_event = NULL;
     }
+
+    d->arch.mem_access_emulate_each_rep = 0;
 }
 
 void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v)
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index f0aeade..f1d7ed6 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -386,6 +386,7 @@ struct arch_domain
 
     /* Mem_access emulation control */
     bool_t mem_access_emulate_enabled;
+    bool_t mem_access_emulate_each_rep;
 } __cacheline_aligned;
 
 #define has_arch_pdevs(d)    (!list_empty(&(d)->arch.pdev_list))
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 794d4d5..ae241f2 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -1007,6 +1007,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_psr_cmt_op_t);
 #define XEN_DOMCTL_MONITOR_OP_ENABLE            0
 #define XEN_DOMCTL_MONITOR_OP_DISABLE           1
 #define XEN_DOMCTL_MONITOR_OP_GET_CAPABILITIES  2
+#define XEN_DOMCTL_MONITOR_OP_EMULATE_EACH_REP  3
 
 #define XEN_DOMCTL_MONITOR_EVENT_WRITE_CTRLREG         0
 #define XEN_DOMCTL_MONITOR_EVENT_MOV_TO_MSR            1
-- 
1.7.9.5


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