[Xen-devel] [PATCH v6 17/19] x86/VPMU: NMI-based VPMU support

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Add support for using NMIs as PMU interrupts.

Most of processing is still performed by vpmu_do_interrupt(). However, since
certain operations are not NMI-safe we defer them to a softint that 
vpmu_do_interrupt()
will schedule:
* For PV guests that would be send_guest_vcpu_virq()
* For HVM guests it's VLAPIC accesses and hvm_get_segment_register() (the later
can be called in privileged profiling mode when the interrupted guest is an HVM 
one).

With send_guest_vcpu_virq() and hvm_get_segment_register() for PV(H) and vlapic
accesses for HVM moved to sofint, the only routines/macros that 
vpmu_do_interrupt()
calls in NMI mode are:
* memcpy()
* querying domain type (is_XX_domain())
* guest_cpu_user_regs()
* XLAT_cpu_user_regs()
* raise_softirq()
* vcpu_vpmu()
* vpmu_ops->arch_vpmu_save()
* vpmu_ops->do_interrupt() (in the future for PVH support)

The latter two only access PMU MSRs with {rd,wr}msrl() (not the _safe versions
which would not be NMI-safe).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
Tested-by: Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/svm/vpmu.c       |   1 +
 xen/arch/x86/hvm/vmx/vpmu_core2.c |   1 +
 xen/arch/x86/hvm/vpmu.c           | 183 +++++++++++++++++++++++++++++++-------
 3 files changed, 152 insertions(+), 33 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/vpmu.c b/xen/arch/x86/hvm/svm/vpmu.c
index 42c3530..8711e86 100644
--- a/xen/arch/x86/hvm/svm/vpmu.c
+++ b/xen/arch/x86/hvm/svm/vpmu.c
@@ -185,6 +185,7 @@ static inline void context_load(struct vcpu *v)
     }
 }
 
+/* Must be NMI-safe */
 static void amd_vpmu_load(struct vcpu *v)
 {
     struct vpmu_struct *vpmu = vcpu_vpmu(v);
diff --git a/xen/arch/x86/hvm/vmx/vpmu_core2.c 
b/xen/arch/x86/hvm/vmx/vpmu_core2.c
index 8182dc3..c06b305 100644
--- a/xen/arch/x86/hvm/vmx/vpmu_core2.c
+++ b/xen/arch/x86/hvm/vmx/vpmu_core2.c
@@ -303,6 +303,7 @@ static inline void __core2_vpmu_save(struct vcpu *v)
         rdmsrl(MSR_CORE_PERF_GLOBAL_STATUS, core2_vpmu_cxt->global_status);
 }
 
+/* Must be NMI-safe */
 static int core2_vpmu_save(struct vcpu *v)
 {
     struct vpmu_struct *vpmu = vcpu_vpmu(v);
diff --git a/xen/arch/x86/hvm/vpmu.c b/xen/arch/x86/hvm/vpmu.c
index 7cb2231..f73ebbb 100644
--- a/xen/arch/x86/hvm/vpmu.c
+++ b/xen/arch/x86/hvm/vpmu.c
@@ -36,6 +36,7 @@
 #include <asm/hvm/svm/svm.h>
 #include <asm/hvm/svm/vmcb.h>
 #include <asm/apic.h>
+#include <asm/nmi.h>
 #include <public/pmu.h>
 
 /*
@@ -48,34 +49,60 @@ uint64_t __read_mostly vpmu_features = 0;
 static void parse_vpmu_param(char *s);
 custom_param("vpmu", parse_vpmu_param);
 
+static void pmu_softnmi(void);
+
 static DEFINE_PER_CPU(struct vcpu *, last_vcpu);
+static DEFINE_PER_CPU(struct vcpu *, sampled_vcpu);
+
+static uint32_t __read_mostly vpmu_interrupt_type = PMU_APIC_VECTOR;
 
 static void __init parse_vpmu_param(char *s)
 {
-    switch ( parse_bool(s) )
-    {
-    case 0:
-        break;
-    default:
-        if ( !strcmp(s, "bts") )
-            vpmu_features |= XENPMU_FEATURE_INTEL_BTS;
-        else if ( *s )
+    char *ss;
+
+    vpmu_mode = XENPMU_MODE_ON;
+    if (*s == '\0')
+        return;
+
+    do {
+        ss = strchr(s, ',');
+        if ( ss )
+            *ss = '\0';
+
+        switch  ( parse_bool(s) )
         {
-            printk("VPMU: unknown flag: %s - vpmu disabled!\n", s);
+        case 0:
+            vpmu_mode = XENPMU_MODE_OFF;
+            return;
+        case -1:
+            if ( !strcmp(s, "nmi") )
+                vpmu_interrupt_type = APIC_DM_NMI;
+            else if ( !strcmp(s, "bts") )
+                vpmu_features |= XENPMU_FEATURE_INTEL_BTS;
+            else if ( !strcmp(s, "priv") )
+            {
+                vpmu_mode &= ~XENPMU_MODE_ON;
+                vpmu_mode |= XENPMU_MODE_PRIV;
+            }
+            else
+            {
+                printk("VPMU: unknown flag: %s - vpmu disabled!\n", s);
+                vpmu_mode = XENPMU_MODE_OFF;
+                return;
+            }
+        default:
             break;
         }
-        /* fall through */
-    case 1:
-        vpmu_mode = XENPMU_MODE_ON;
-        break;
-    }
+
+        s = ss + 1;
+    } while ( ss );
 }
 
 void vpmu_lvtpc_update(uint32_t val)
 {
     struct vpmu_struct *vpmu = vcpu_vpmu(current);
 
-    vpmu->hw_lapic_lvtpc = PMU_APIC_VECTOR | (val & APIC_LVT_MASKED);
+    vpmu->hw_lapic_lvtpc = vpmu_interrupt_type | (val & APIC_LVT_MASKED);
 
     /* Postpone APIC updates for PV guests if PMU interrupt is pending */
     if ( !is_pv_domain(current->domain) ||
@@ -84,6 +111,27 @@ void vpmu_lvtpc_update(uint32_t val)
         apic_write(APIC_LVTPC, vpmu->hw_lapic_lvtpc);
 }
 
+static void vpmu_send_nmi(struct vcpu *v)
+{
+    struct vlapic *vlapic;
+    u32 vlapic_lvtpc;
+    unsigned char int_vec;
+
+    ASSERT( is_hvm_vcpu(v) );
+
+    vlapic = vcpu_vlapic(v);
+    if ( !is_vlapic_lvtpc_enabled(vlapic) )
+        return;
+
+    vlapic_lvtpc = vlapic_get_reg(vlapic, APIC_LVTPC);
+    int_vec = vlapic_lvtpc & APIC_VECTOR_MASK;
+
+    if ( GET_APIC_DELIVERY_MODE(vlapic_lvtpc) == APIC_MODE_FIXED )
+        vlapic_set_irq(vcpu_vlapic(v), int_vec, 0);
+    else
+        v->nmi_pending = 1;
+}
+
 int vpmu_do_msr(unsigned int msr, uint64_t *msr_content, uint8_t rw)
 {
     struct vpmu_struct *vpmu = vcpu_vpmu(current);
@@ -125,6 +173,7 @@ int vpmu_do_msr(unsigned int msr, uint64_t *msr_content, 
uint8_t rw)
     return 0;
 }
 
+/* This routine may be called in NMI context */
 int vpmu_do_interrupt(struct cpu_user_regs *regs)
 {
     struct vcpu *v = current;
@@ -209,9 +258,13 @@ int vpmu_do_interrupt(struct cpu_user_regs *regs)
             memcpy(&v->arch.vpmu.xenpmu_data->pmu.r.regs,
                    gregs, sizeof(struct cpu_user_regs));
 
-            hvm_get_segment_register(current, x86_seg_cs, &cs);
-            gregs = &v->arch.vpmu.xenpmu_data->pmu.r.regs;
-            gregs->cs = cs.attr.fields.dpl;
+            /* This is unsafe in NMI context, we'll do it in softint handler */
+            if ( !(vpmu_interrupt_type & APIC_DM_NMI ) )
+            {
+                hvm_get_segment_register(current, x86_seg_cs, &cs);
+                gregs = &v->arch.vpmu.xenpmu_data->pmu.r.regs;
+                gregs->cs = cs.attr.fields.dpl;
+            }
         }
 
         v->arch.vpmu.xenpmu_data->domain_id = current->domain->domain_id;
@@ -222,30 +275,30 @@ int vpmu_do_interrupt(struct cpu_user_regs *regs)
         apic_write(APIC_LVTPC, vpmu->hw_lapic_lvtpc | APIC_LVT_MASKED);
         vpmu->hw_lapic_lvtpc |= APIC_LVT_MASKED;
 
-        send_guest_vcpu_virq(v, VIRQ_XENPMU);
+        if ( vpmu_interrupt_type & APIC_DM_NMI )
+        {
+            per_cpu(sampled_vcpu, smp_processor_id()) = current;
+            raise_softirq(PMU_SOFTIRQ);
+        }
+        else
+            send_guest_vcpu_virq(v, VIRQ_XENPMU);
 
         return 1;
     }
 
     if ( vpmu->arch_vpmu_ops )
     {
-        struct vlapic *vlapic = vcpu_vlapic(v);
-        u32 vlapic_lvtpc;
-        unsigned char int_vec;
-
         if ( !vpmu->arch_vpmu_ops->do_interrupt(regs) )
             return 0;
 
-        if ( !is_vlapic_lvtpc_enabled(vlapic) )
-            return 1;
-
-        vlapic_lvtpc = vlapic_get_reg(vlapic, APIC_LVTPC);
-        int_vec = vlapic_lvtpc & APIC_VECTOR_MASK;
-
-        if ( GET_APIC_DELIVERY_MODE(vlapic_lvtpc) == APIC_MODE_FIXED )
-            vlapic_set_irq(vcpu_vlapic(v), int_vec, 0);
+        if ( vpmu_interrupt_type & APIC_DM_NMI )
+        {
+            per_cpu(sampled_vcpu, smp_processor_id()) = current;
+            raise_softirq(PMU_SOFTIRQ);
+        }
         else
-            v->nmi_pending = 1;
+            vpmu_send_nmi(v);
+
         return 1;
     }
 
@@ -276,6 +329,8 @@ static void vpmu_save_force(void *arg)
     vpmu_reset(vpmu, VPMU_CONTEXT_SAVE);
 
     per_cpu(last_vcpu, smp_processor_id()) = NULL;
+
+    pmu_softnmi();
 }
 
 void vpmu_save(struct vcpu *v)
@@ -293,7 +348,10 @@ void vpmu_save(struct vcpu *v)
         if ( vpmu->arch_vpmu_ops->arch_vpmu_save(v) )
             vpmu_reset(vpmu, VPMU_CONTEXT_LOADED);
 
-    apic_write(APIC_LVTPC, PMU_APIC_VECTOR | APIC_LVT_MASKED);
+    apic_write(APIC_LVTPC, vpmu_interrupt_type | APIC_LVT_MASKED);
+
+    /* Make sure there are no outstanding PMU NMIs */
+    pmu_softnmi();
 }
 
 void vpmu_load(struct vcpu *v)
@@ -338,6 +396,8 @@ void vpmu_load(struct vcpu *v)
         vpmu_save_force(prev);
         vpmu_reset(vpmu, VPMU_CONTEXT_LOADED);
 
+        pmu_softnmi();
+
         vpmu = vcpu_vpmu(v);
     }
 
@@ -442,11 +502,53 @@ static void vpmu_unload_all(void)
     }
 }
 
+/* Process the softirq set by PMU NMI handler */
+static void pmu_softnmi(void)
+{
+    struct cpu_user_regs *regs;
+    struct vcpu *v, *sampled = per_cpu(sampled_vcpu, smp_processor_id());
+
+    if ( sampled == NULL )
+        return;
+    per_cpu(sampled_vcpu, smp_processor_id()) = NULL;
+
+    if ( (vpmu_mode & XENPMU_MODE_PRIV) ||
+         (sampled->domain->domain_id >= DOMID_FIRST_RESERVED) )
+        v = hardware_domain->vcpu[smp_processor_id() %
+                                  hardware_domain->max_vcpus];
+    else
+    {
+        if ( is_hvm_domain(sampled->domain) )
+        {
+            vpmu_send_nmi(sampled);
+            return;
+        }
+        v = sampled;
+    }
+
+    regs = &v->arch.vpmu.xenpmu_data->pmu.r.regs;
+    if ( !is_pv_domain(sampled->domain) )
+    {
+        struct segment_register cs;
+
+        hvm_get_segment_register(sampled, x86_seg_cs, &cs);
+        regs->cs = cs.attr.fields.dpl;
+    }
+
+    send_guest_vcpu_virq(v, VIRQ_XENPMU);
+}
+
+int pmu_nmi_interrupt(struct cpu_user_regs *regs, int cpu)
+{
+    return vpmu_do_interrupt(regs);
+}
+
 static int pvpmu_init(struct domain *d, xen_pmu_params_t *params)
 {
     struct vcpu *v;
     struct page_info *page;
     uint64_t gfn = params->d.val;
+    static bool_t __read_mostly pvpmu_initted = 0;
 
     if ( !is_pv_domain(d) )
         return -EINVAL;
@@ -472,6 +574,21 @@ static int pvpmu_init(struct domain *d, xen_pmu_params_t 
*params)
         return -EINVAL;
     }
 
+    if ( !pvpmu_initted )
+    {
+        if (reserve_lapic_nmi() == 0)
+            set_nmi_callback(pmu_nmi_interrupt);
+        else
+        {
+            printk("Failed to reserve PMU NMI\n");
+            put_page(page);
+            return -EBUSY;
+        }
+        open_softirq(PMU_SOFTIRQ, pmu_softnmi);
+
+        pvpmu_initted = 1;
+    }
+
     vpmu_initialise(v);
 
     return 0;
-- 
1.8.1.4


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