[PATCH 3.12 011/133] KVM: x86: limit PIT timer frequency

Greg Kroah-Hartman
2014-02-04T21:08:00Z

From: Marcelo Tosatti <mtosatti@redhat.com>

commit 9ed96e87c5748de4c2807ef17e81287c7304186c upstream.

Limit PIT timer frequency similarly to the limit applied by
LAPIC timer.

Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/i8254.c | 18 ++++++++++++++++++
arch/x86/kvm/lapic.c | 3 ---
arch/x86/kvm/x86.c | 3 +++
arch/x86/kvm/x86.h | 2 ++
4 files changed, 23 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -37,6 +37,7 @@

#include "irq.h"
#include "i8254.h"
+#include "x86.h"

#ifndef CONFIG_X86_64
#define mod_64(x, y) ((x) - (y) * div64_u64(x, y))
@@ -349,6 +350,23 @@ static void create_pit_timer(struct kvm
atomic_set(&ps->pending, 0);
ps->irq_ack = 1;

+ /*
+ * Do not allow the guest to program periodic timers with small
+ * interval, since the hrtimers are not throttled by the host
+ * scheduler.
+ */
+ if (ps->is_periodic) {
+ s64 min_period = min_timer_period_us * 1000LL;
+
+ if (ps->period < min_period) {
+ pr_info_ratelimited(
+ "kvm: requested %lld ns "
+ "i8254 timer period limited to %lld ns\n",
+ ps->period, min_period);
+ ps->period = min_period;
+ }
+ }
+
hrtimer_start(&ps->timer, ktime_add_ns(ktime_get(), interval),
HRTIMER_MODE_ABS);
}
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -71,9 +71,6 @@
#define VEC_POS(v) ((v) & (32 - 1))
#define REG_POS(v) (((v) >> 5) << 4)

-static unsigned int min_timer_period_us = 500;
-module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
-
static inline void apic_set_reg(struct kvm_lapic *apic, int reg_off, u32 val)
{
*((u32 *) (apic->regs + reg_off)) = val;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -94,6 +94,9 @@ EXPORT_SYMBOL_GPL(kvm_x86_ops);
static bool ignore_msrs = 0;
module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);

+unsigned int min_timer_period_us = 500;
+module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
+
bool kvm_has_tsc_control;
EXPORT_SYMBOL_GPL(kvm_has_tsc_control);
u32 kvm_max_guest_tsc_khz;
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -124,5 +124,7 @@ int kvm_write_guest_virt_system(struct x

extern u64 host_xcr0;

+extern unsigned int min_timer_period_us;
+
extern struct static_key kvm_no_apic_vcpu;
#endif