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    Subject[PATCH 3.12 011/133] KVM: x86: limit PIT timer frequency
    Date
    3.12-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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



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