[Qemu-devel] [PATCH 1/5] target-i386: kvm: Allocate kvm_msrs struct once per VCPU

[Eduardo Habkost <ehabkost@redhat.com>]

Instead of using 2400 bytes in the stack for 150 MSR entries in
kvm_get_msrs() and kvm_put_msrs(), allocate a buffer once for
each VCPU.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 target-i386/cpu-qom.h |  4 ++++
 target-i386/kvm.c     | 37 +++++++++++++++++++------------------
 2 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
index e3bfe9d..f349b30 100644
--- a/target-i386/cpu-qom.h
+++ b/target-i386/cpu-qom.h
@@ -69,6 +69,8 @@ typedef struct X86CPUClass {
     void (*parent_reset)(CPUState *cpu);
 } X86CPUClass;
 
+struct kvm_msrs;
+
 /**
  * X86CPU:
  * @env: #CPUX86State
@@ -119,6 +121,8 @@ typedef struct X86CPU {
     struct DeviceState *apic_state;
     struct MemoryRegion *cpu_as_root, *cpu_as_mem, *smram;
     Notifier machine_done;
+
+    struct kvm_msrs *kvm_msr_buf;
 } X86CPU;
 
 static inline X86CPU *x86_env_get_cpu(CPUX86State *env)
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 6dc9846..660b2d9 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -52,6 +52,9 @@
 #define MSR_KVM_WALL_CLOCK  0x11
 #define MSR_KVM_SYSTEM_TIME 0x12
 
+#define MSR_BUF_SIZE \
+    (sizeof(struct kvm_msrs) + 150 * sizeof(struct kvm_msr_entry))
+
 #ifndef BUS_MCEERR_AR
 #define BUS_MCEERR_AR 4
 #endif
@@ -841,6 +844,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
     if (has_xsave) {
         env->kvm_xsave_buf = qemu_memalign(4096, sizeof(struct kvm_xsave));
     }
+    cpu->kvm_msr_buf = g_malloc0(MSR_BUF_SIZE);
 
     if (env->features[FEAT_1_EDX] & CPUID_MTRR) {
         has_msr_mtrr = true;
@@ -1349,6 +1353,11 @@ static void kvm_msr_entry_set(struct kvm_msr_entry *entry,
     entry->data = value;
 }
 
+static void kvm_msr_buf_reset(X86CPU *cpu)
+{
+    memset(cpu->kvm_msr_buf, 0, MSR_BUF_SIZE);
+}
+
 static int kvm_put_tscdeadline_msr(X86CPU *cpu)
 {
     CPUX86State *env = &cpu->env;
@@ -1397,13 +1406,11 @@ static int kvm_put_msr_feature_control(X86CPU *cpu)
 static int kvm_put_msrs(X86CPU *cpu, int level)
 {
     CPUX86State *env = &cpu->env;
-    struct {
-        struct kvm_msrs info;
-        struct kvm_msr_entry entries[150];
-    } msr_data;
-    struct kvm_msr_entry *msrs = msr_data.entries;
+    struct kvm_msr_entry *msrs = cpu->kvm_msr_buf->entries;
     int n = 0, i;
 
+    kvm_msr_buf_reset(cpu);
+
     kvm_msr_entry_set(&msrs[n++], MSR_IA32_SYSENTER_CS, env->sysenter_cs);
     kvm_msr_entry_set(&msrs[n++], MSR_IA32_SYSENTER_ESP, env->sysenter_esp);
     kvm_msr_entry_set(&msrs[n++], MSR_IA32_SYSENTER_EIP, env->sysenter_eip);
@@ -1562,11 +1569,9 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
         }
     }
 
-    msr_data.info = (struct kvm_msrs) {
-        .nmsrs = n,
-    };
+    cpu->kvm_msr_buf->nmsrs = n;
 
-    return kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, &msr_data);
+    return kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, cpu->kvm_msr_buf);
 
 }
 
@@ -1775,13 +1780,11 @@ static int kvm_get_sregs(X86CPU *cpu)
 static int kvm_get_msrs(X86CPU *cpu)
 {
     CPUX86State *env = &cpu->env;
-    struct {
-        struct kvm_msrs info;
-        struct kvm_msr_entry entries[150];
-    } msr_data;
-    struct kvm_msr_entry *msrs = msr_data.entries;
+    struct kvm_msr_entry *msrs = cpu->kvm_msr_buf->entries;
     int ret, i, n;
 
+    kvm_msr_buf_reset(cpu);
+
     n = 0;
     msrs[n++].index = MSR_IA32_SYSENTER_CS;
     msrs[n++].index = MSR_IA32_SYSENTER_ESP;
@@ -1904,11 +1907,9 @@ static int kvm_get_msrs(X86CPU *cpu)
         }
     }
 
-    msr_data.info = (struct kvm_msrs) {
-        .nmsrs = n,
-    };
+    cpu->kvm_msr_buf->nmsrs = n;
 
-    ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_MSRS, &msr_data);
+    ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_MSRS, cpu->kvm_msr_buf);
     if (ret < 0) {
         return ret;
     }
-- 
2.1.0