Commit 18863bdd authored by Avi Kivity's avatar Avi Kivity
Browse files

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: default avatarAvi Kivity <avi@redhat.com>
parent 44ea2b17
......@@ -809,4 +809,7 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);
int kvm_cpu_get_interrupt(struct kvm_vcpu *v);
void kvm_define_shared_msr(unsigned index, u32 msr);
void kvm_set_shared_msr(unsigned index, u64 val);
#endif /* _ASM_X86_KVM_HOST_H */
......@@ -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
......
......@@ -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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