svm: Greatly reduce total number of CR8 intercepts

This patch reduces the number of CR8 intercept to a fraction of the
number of CR8 intercepts without.  First, CR8 read intercepts are
completely disabled since the SVM vTPR is kept kept in sync with the
HVM vLAPIC TPR.  Second, CR8 write intercepts are enabled and disabled
based upon certain conditions.  Most of the time, CR8 write intercepts
are disabled.  They are enabled only when there is a pending interrupt
that can't be delivered because of either the current ISR or TPR (aka
PPR) because this is the only time the TPR matters.

With this patch, the number of CR8 intercepts dropped from around
10,000,000 to around 6,000 during boot of Windows 2003 Server 64-bit
(this is a rough estimate).

Signed-off-by: Travis Betak <travis.betak@amd.com>
Signed-off-by: Keir Fraser <keir@xensource.com>
xen-unstable changeset:   15844:924c153e0cf90e7c6f9033842d702d0fbc122d29
xen-unstable date:        Mon Sep 10 16:13:13 2007 +0100

diff --git a/xen/arch/x86/hvm/svm/intr.c b/xen/arch/x86/hvm/svm/intr.c
index 0730586308c748bdfc81e4fbe0b75319c45011c9..a4aa30bc935684ebad29d0ca63271dbc123ac416 100644 (file)
--- a/xen/arch/x86/hvm/svm/intr.c
+++ b/xen/arch/x86/hvm/svm/intr.c
@@ -31,6 +31,7 @@
 #include <asm/hvm/hvm.h>
 #include <asm/hvm/io.h>
 #include <asm/hvm/support.h>
+#include <asm/hvm/vlapic.h>
 #include <asm/hvm/svm/svm.h>
 #include <asm/hvm/svm/intr.h>
 #include <xen/event.h>
@@ -59,6 +60,32 @@ static inline int svm_inject_extint(struct vcpu *v, int trap)
 
     return 0;
 }
+
+static void update_cr8_intercept(
+    struct vcpu *v, int intr_window_enabled)
+{
+    struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
+    struct vlapic *vlapic = vcpu_vlapic(v);
+    int max_irr;
+
+    vmcb->cr_intercepts &= ~CR_INTERCEPT_CR8_WRITE;
+ 
+    /* 
+     * If ExtInts are masked then that dominates the TPR --- the 'interrupt
+     * window' has already been enabled in this case.
+     */
+    if ( intr_window_enabled )
+        return;
+
+    /* Is there an interrupt pending at the LAPIC? Nothing to do if not. */
+    if ( !vlapic_enabled(vlapic) || 
+         ((max_irr = vlapic_find_highest_irr(vlapic)) == -1) )
+        return;
+
+    /* Highest-priority pending interrupt is masked by the TPR? */
+    if ( (vmcb->vintr.fields.tpr & 0xf) >= (max_irr >> 4) )
+        vmcb->cr_intercepts |= CR_INTERCEPT_CR8_WRITE;
+}
     
 asmlinkage void svm_intr_assist(void) 
 {
@@ -66,6 +93,7 @@ asmlinkage void svm_intr_assist(void)
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
     int intr_type = APIC_DM_EXTINT;
     int intr_vector = -1;
+    int intr_window_enabled = 0;
 
     /*
      * Previous Interrupt delivery caused this intercept?
@@ -83,7 +111,7 @@ asmlinkage void svm_intr_assist(void)
         vmcb->exitintinfo.bytes = 0;
         HVMTRACE_1D(REINJ_VIRQ, v, intr_vector);
         svm_inject_extint(v, intr_vector);
-        return;
+        goto out;
     }
 
     /*
@@ -92,13 +120,13 @@ asmlinkage void svm_intr_assist(void)
      * external physical interrupt was pending when we executed VMRUN.
      */
     if ( vmcb->vintr.fields.irq )
-        return;
+        goto out;
 
     /* Crank the handle on interrupt state and check for new interrrupts. */
     pt_update_irq(v);
     hvm_set_callback_irq_level();
     if ( !cpu_has_pending_irq(v) )
-        return;
+        goto out;
 
     /*
      * If the guest can't take an interrupt right now, create a 'fake'
@@ -122,7 +150,8 @@ asmlinkage void svm_intr_assist(void)
         vmcb->general1_intercepts |= GENERAL1_INTERCEPT_VINTR;
         HVMTRACE_2D(INJ_VIRQ, v, 0x0, /*fake=*/ 1);
         svm_inject_extint(v, 0x0); /* actual vector doesn't matter */
-        return;
+        intr_window_enabled = 1;
+        goto out;
     }
 
     /* Okay, we can deliver the interrupt: grab it and update PIC state. */
@@ -133,6 +162,9 @@ asmlinkage void svm_intr_assist(void)
     svm_inject_extint(v, intr_vector);
 
     pt_intr_post(v, intr_vector, intr_type);
+
+ out:
+    update_cr8_intercept(v, intr_window_enabled);
 }
 
 /*

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 69e6d733ec879ed0b45b5f5047a566a941cc6030..270dace6040fc7a042ce5398f894366340569ad1 100644 (file)
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2422,6 +2422,16 @@ asmlinkage void svm_vmexit_handler(struct cpu_user_regs *regs)
     struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
     int inst_len, rc;
 
+    /*
+     * Before doing anything else, we need to sync up the VLAPIC's TPR with
+     * SVM's vTPR if CR8 writes are currently disabled.  It's OK if the 
+     * guest doesn't touch the CR8 (e.g. 32-bit Windows) because we update
+     * the vTPR on MMIO writes to the TPR
+     */
+    if ( !(vmcb->cr_intercepts & CR_INTERCEPT_CR8_WRITE) )
+        vlapic_set_reg(vcpu_vlapic(v), APIC_TASKPRI,
+                       (vmcb->vintr.fields.tpr & 0x0F) << 4);
+
     exit_reason = vmcb->exitcode;
 
     HVMTRACE_2D(VMEXIT, v, vmcb->rip, exit_reason);

diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
index b8df6f90ede96cdaf60b34dbf986abb7a225b5fd..41b61969ce1be8b80360e6379ea682f27b2cda48 100644 (file)
--- a/xen/arch/x86/hvm/svm/vmcb.c
+++ b/xen/arch/x86/hvm/svm/vmcb.c
@@ -131,8 +131,14 @@ static int construct_vmcb(struct vcpu *v)
     /* Intercept all debug-register writes. */
     vmcb->dr_intercepts = ~0u;
 
-    /* Intercept all control-register accesses, except to CR2. */
-    vmcb->cr_intercepts = ~(CR_INTERCEPT_CR2_READ | CR_INTERCEPT_CR2_WRITE);
+    /*
+     * Intercept all control-register accesses except for CR2 reads/writes
+     * and CR8 reads (and actually CR8 writes, but that's a special case
+     * that's handled in svm/intr.c). 
+     */
+    vmcb->cr_intercepts = ~(CR_INTERCEPT_CR2_READ |
+                            CR_INTERCEPT_CR2_WRITE |
+                            CR_INTERCEPT_CR8_READ);
 
     /* I/O and MSR permission bitmaps. */
     arch_svm->msrpm = alloc_xenheap_pages(get_order_from_bytes(MSRPM_SIZE));