[Xen-devel] [PATCH 2/6] x86: save GUEST_BNDCFGS on context switch...

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

...to avoid the need for a VMCS reload when the value of MSR_IA32_BNDCFGS is
read by the tool-stack.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c     | 18 +++++++++++++++---
 xen/arch/x86/hvm/vmx/vmx.c |  3 +++
 xen/include/asm-x86/msr.h  |  5 +++++
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 5fd5478b7d..b86aed7c24 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -311,6 +311,7 @@ int hvm_set_guest_pat(struct vcpu *v, u64 guest_pat)
 bool hvm_set_guest_bndcfgs(struct vcpu *v, uint64_t val)
 {
     const struct cpuid_policy *cp = v->domain->arch.cpuid;
+    struct vcpu_msrs *msrs = v->arch.msrs;
 
     if ( !cp->feat.mpx )
         return false;
@@ -347,7 +348,8 @@ bool hvm_set_guest_bndcfgs(struct vcpu *v, uint64_t val)
             /* nothing, best effort only */;
     }
 
-    hvm_funcs.set_guest_bndcfgs(v, val);
+    msrs->bndcfgs.raw = val;
+    hvm_funcs.set_guest_bndcfgs(v, msrs->bndcfgs.raw);
 
     return true;
 }
@@ -355,12 +357,22 @@ bool hvm_set_guest_bndcfgs(struct vcpu *v, uint64_t val)
 bool hvm_get_guest_bndcfgs(struct vcpu *v, uint64_t *val)
 {
     const struct cpuid_policy *cp = v->domain->arch.cpuid;
+    struct vcpu_msrs *msrs = v->arch.msrs;
 
     if ( !cp->feat.mpx )
         return false;
 
-    ASSERT(hvm_funcs.get_guest_bndcfgs);
-    *val = hvm_funcs.get_guest_bndcfgs(v);
+    /*
+     * The value only need be read in current context as a context
+     * switch will save the value into msrs->bndcfgs.
+     */
+    if ( v == current )
+    {
+        ASSERT(hvm_funcs.get_guest_bndcfgs);
+        msrs->bndcfgs.raw = hvm_funcs.get_guest_bndcfgs(v);
+    }
+
+    *val = msrs->bndcfgs.raw;
 
     return true;
 }
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 4bfabe8d0e..7dba92da45 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -497,6 +497,9 @@ static void vmx_restore_host_msrs(void)
 
 static void vmx_save_guest_msrs(struct vcpu *v)
 {
+    if ( cpu_has_mpx && cpu_has_vmx_mpx )
+        __vmread(GUEST_BNDCFGS, &v->arch.msrs->bndcfgs.raw);
+
     /*
      * We cannot cache SHADOW_GS_BASE while the VCPU runs, as it can
      * be updated at any time via SWAPGS, which we cannot trap.
diff --git a/xen/include/asm-x86/msr.h b/xen/include/asm-x86/msr.h
index ad8688a61f..c69ce56963 100644
--- a/xen/include/asm-x86/msr.h
+++ b/xen/include/asm-x86/msr.h
@@ -305,6 +305,11 @@ struct vcpu_msrs
      * values here may be stale in current context.
      */
     uint32_t dr_mask[4];
+
+    /* 0x00000d90 - MSR_IA32_BNDCFGS */
+    struct {
+        uint64_t raw;
+    } bndcfgs;
 };
 
 void init_guest_msr_policy(void);
-- 
2.20.1


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