KVM: x86: limit PIT timer frequency

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

Cc: stable@kernel.org
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

4 files changed, 23 insertions, 3 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 412a5aa0ef94..518d86471b76 100644
--- 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 *kvm, u32 val, int is_period)
         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);
 }
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 206715bc603d..1ac009390780 100644
--- 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;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1dc0359e2095..0fd2bd78fccf 100644
--- 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;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 587fb9ede436..8da5823bcde6 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -125,5 +125,7 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
 #define KVM_SUPPORTED_XCR0      (XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
 extern u64 host_xcr0;
 
+extern unsigned int min_timer_period_us;
+
 extern struct static_key kvm_no_apic_vcpu;
 #endif