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authorAvi Kivity <avi@redhat.com>2009-09-07 11:12:18 +0300
committerAvi Kivity <avi@redhat.com>2009-12-03 09:32:21 +0200
commit18863bdd60f895f3b3ba16b15e8331aee781e8ec (patch)
tree2d0e456a8d2dc12def13f2fed386ca9e5a440823 /arch/x86/kvm
parent44ea2b1758d88ad822e65b1c4c21ca6164494e27 (diff)
downloadop-kernel-dev-18863bdd60f895f3b3ba16b15e8331aee781e8ec.zip
op-kernel-dev-18863bdd60f895f3b3ba16b15e8331aee781e8ec.tar.gz
KVM: x86 shared msr infrastructure
The various syscall-related MSRs are fairly expensive to switch. Currently we switch them on every vcpu preemption, which is far too often: - if we're switching to a kernel thread (idle task, threaded interrupt, kernel-mode virtio server (vhost-net), for example) and back, then there's no need to switch those MSRs since kernel threasd won't be exiting to userspace. - if we're switching to another guest running an identical OS, most likely those MSRs will have the same value, so there's little point in reloading them. - if we're running the same OS on the guest and host, the MSRs will have identical values and reloading is unnecessary. This patch uses the new user return notifiers to implement last-minute switching, and checks the msr values to avoid unnecessary reloading. Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r--arch/x86/kvm/Kconfig1
-rw-r--r--arch/x86/kvm/x86.c81
2 files changed, 82 insertions, 0 deletions
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index b84e571..4cd4983 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -28,6 +28,7 @@ config KVM
select HAVE_KVM_IRQCHIP
select HAVE_KVM_EVENTFD
select KVM_APIC_ARCHITECTURE
+ select USER_RETURN_NOTIFIER
---help---
Support hosting fully virtualized guest machines using hardware
virtualization extensions. You will need a fairly recent
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e16cdc9..58c5cdd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -37,6 +37,7 @@
#include <linux/iommu.h>
#include <linux/intel-iommu.h>
#include <linux/cpufreq.h>
+#include <linux/user-return-notifier.h>
#include <trace/events/kvm.h>
#undef TRACE_INCLUDE_FILE
#define CREATE_TRACE_POINTS
@@ -87,6 +88,25 @@ EXPORT_SYMBOL_GPL(kvm_x86_ops);
int ignore_msrs = 0;
module_param_named(ignore_msrs, ignore_msrs, bool, S_IRUGO | S_IWUSR);
+#define KVM_NR_SHARED_MSRS 16
+
+struct kvm_shared_msrs_global {
+ int nr;
+ struct kvm_shared_msr {
+ u32 msr;
+ u64 value;
+ } msrs[KVM_NR_SHARED_MSRS];
+};
+
+struct kvm_shared_msrs {
+ struct user_return_notifier urn;
+ bool registered;
+ u64 current_value[KVM_NR_SHARED_MSRS];
+};
+
+static struct kvm_shared_msrs_global __read_mostly shared_msrs_global;
+static DEFINE_PER_CPU(struct kvm_shared_msrs, shared_msrs);
+
struct kvm_stats_debugfs_item debugfs_entries[] = {
{ "pf_fixed", VCPU_STAT(pf_fixed) },
{ "pf_guest", VCPU_STAT(pf_guest) },
@@ -123,6 +143,64 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
{ NULL }
};
+static void kvm_on_user_return(struct user_return_notifier *urn)
+{
+ unsigned slot;
+ struct kvm_shared_msr *global;
+ struct kvm_shared_msrs *locals
+ = container_of(urn, struct kvm_shared_msrs, urn);
+
+ for (slot = 0; slot < shared_msrs_global.nr; ++slot) {
+ global = &shared_msrs_global.msrs[slot];
+ if (global->value != locals->current_value[slot]) {
+ wrmsrl(global->msr, global->value);
+ locals->current_value[slot] = global->value;
+ }
+ }
+ locals->registered = false;
+ user_return_notifier_unregister(urn);
+}
+
+void kvm_define_shared_msr(unsigned slot, u32 msr)
+{
+ int cpu;
+ u64 value;
+
+ if (slot >= shared_msrs_global.nr)
+ shared_msrs_global.nr = slot + 1;
+ shared_msrs_global.msrs[slot].msr = msr;
+ rdmsrl_safe(msr, &value);
+ shared_msrs_global.msrs[slot].value = value;
+ for_each_online_cpu(cpu)
+ per_cpu(shared_msrs, cpu).current_value[slot] = value;
+}
+EXPORT_SYMBOL_GPL(kvm_define_shared_msr);
+
+static void kvm_shared_msr_cpu_online(void)
+{
+ unsigned i;
+ struct kvm_shared_msrs *locals = &__get_cpu_var(shared_msrs);
+
+ for (i = 0; i < shared_msrs_global.nr; ++i)
+ locals->current_value[i] = shared_msrs_global.msrs[i].value;
+}
+
+void kvm_set_shared_msr(unsigned slot, u64 value)
+{
+ struct kvm_shared_msrs *smsr = &__get_cpu_var(shared_msrs);
+
+ if (value == smsr->current_value[slot])
+ return;
+ smsr->current_value[slot] = value;
+ wrmsrl(shared_msrs_global.msrs[slot].msr, value);
+ if (!smsr->registered) {
+ smsr->urn.on_user_return = kvm_on_user_return;
+ user_return_notifier_register(&smsr->urn);
+ smsr->registered = true;
+ }
+}
+EXPORT_SYMBOL_GPL(kvm_set_shared_msr);
+
unsigned long segment_base(u16 selector)
{
struct descriptor_table gdt;
@@ -4815,6 +4893,9 @@ int kvm_arch_hardware_enable(void *garbage)
int cpu = raw_smp_processor_id();
per_cpu(cpu_tsc_khz, cpu) = 0;
}
+
+ kvm_shared_msr_cpu_online();
+
return kvm_x86_ops->hardware_enable(garbage);
}
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