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    SubjectRe: [PATCH RFC dontapply 5/5] kvm_para: guest side for eoi avoidance
    On Mon, Apr 23, 2012 at 05:04:40PM +0300, Michael S. Tsirkin wrote:
    > The idea is simple: there's a bit, per APIC, in guest memory,
    > that tells the guest that it does not need EOI.
    > Guest tests it using a single est and clear operation - this is
    > necessary so that host can detect interrupt nesting - and if set, it can
    > skip the EOI MSR.
    >
    > This patch is not final yet, pls don't apply
    > until host side is also finalized. Including
    > it here for completeness to show another user
    > of the new eoi_write interface.
    >
    > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    > ---
    > arch/x86/include/asm/bitops.h | 6 +++-
    > arch/x86/include/asm/kvm_para.h | 2 +
    > arch/x86/kernel/kvm.c | 51 ++++++++++++++++++++++++++++++++++++--
    > 3 files changed, 54 insertions(+), 5 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
    > index b97596e..c9c70ea 100644
    > --- a/arch/x86/include/asm/bitops.h
    > +++ b/arch/x86/include/asm/bitops.h
    > @@ -26,11 +26,13 @@
    > #if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 1)
    > /* Technically wrong, but this avoids compilation errors on some gcc
    > versions. */
    > -#define BITOP_ADDR(x) "=m" (*(volatile long *) (x))
    > +#define BITOP_ADDR_CONSTRAINT "=m"
    > #else
    > -#define BITOP_ADDR(x) "+m" (*(volatile long *) (x))
    > +#define BITOP_ADDR_CONSTRAINT "+m"
    > #endif
    >
    > +#define BITOP_ADDR(x) BITOP_ADDR_CONSTRAINT (*(volatile long *) (x))
    > +
    > #define ADDR BITOP_ADDR(addr)
    >
    > /*
    > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
    > index 734c376..195840d 100644
    > --- a/arch/x86/include/asm/kvm_para.h
    > +++ b/arch/x86/include/asm/kvm_para.h
    > @@ -22,6 +22,7 @@
    > #define KVM_FEATURE_CLOCKSOURCE2 3
    > #define KVM_FEATURE_ASYNC_PF 4
    > #define KVM_FEATURE_STEAL_TIME 5
    > +#define KVM_FEATURE_EOI 6
    >
    > /* The last 8 bits are used to indicate how to interpret the flags field
    > * in pvclock structure. If no bits are set, all flags are ignored.
    > @@ -37,6 +38,7 @@
    > #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
    > #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
    > #define MSR_KVM_STEAL_TIME 0x4b564d03
    > +#define MSR_KVM_EOI_EN 0x4b564d04
    >
    > struct kvm_steal_time {
    > __u64 steal;
    > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
    > index b8ba6e4..ad66cdd 100644
    > --- a/arch/x86/kernel/kvm.c
    > +++ b/arch/x86/kernel/kvm.c
    > @@ -39,6 +39,8 @@
    > #include <asm/desc.h>
    > #include <asm/tlbflush.h>
    > #include <asm/idle.h>
    > +#include <asm/apic.h>
    > +#include <asm/apicdef.h>
    >
    > static int kvmapf = 1;
    >
    > @@ -290,6 +292,27 @@ static void kvm_register_steal_time(void)
    > cpu, __pa(st));
    > }
    >
    > +static DEFINE_PER_CPU(u16, kvm_apic_eoi) __aligned(2) = 0;
    > +
    > +/* Our own copy of __test_and_clear_bit to make sure
    > + * it is done with a single instruction */
    > +static inline int kvm_test_and_clear_bit(int nr, volatile u16* addr)
    > +{
    > + int oldbit;
    > +
    > + asm volatile("btr %2,%1\n\t"
    > + "sbb %0,%0"
    > + : "=r" (oldbit), BITOP_ADDR_CONSTRAINT(*addr) : "Ir" (nr));
    > + return oldbit;
    > +}
    > +
    > +static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
    > +{
    > + if (kvm_test_and_clear_bit(0, &__get_cpu_var(kvm_apic_eoi)))
    > + return;
    > + apic->write(APIC_EOI, APIC_EOI_ACK);
    > +}
    > +
    > void __cpuinit kvm_guest_cpu_init(void)
    > {
    > if (!kvm_para_available())
    > @@ -307,11 +330,17 @@ void __cpuinit kvm_guest_cpu_init(void)
    > smp_processor_id());
    > }
    >
    > + if (kvm_para_has_feature(KVM_FEATURE_EOI)) {
    > + __get_cpu_var(kvm_apic_eoi) = 0;
    > + wrmsrl(MSR_KVM_EOI_EN, __pa(&__get_cpu_var(kvm_apic_eoi)) |
    > + KVM_MSR_ENABLED);
    > + }
    > +
    > if (has_steal_clock)
    > kvm_register_steal_time();
    > }
    >
    > -static void kvm_pv_disable_apf(void *unused)
    > +static void kvm_pv_disable_apf(void)
    > {
    > if (!__get_cpu_var(apf_reason).enabled)
    > return;
    > @@ -323,11 +352,18 @@ static void kvm_pv_disable_apf(void *unused)
    > smp_processor_id());
    > }
    >
    > +static void kvm_pv_guest_cpu_reboot(void *unused)
    > +{
    > + if (kvm_para_has_feature(KVM_FEATURE_EOI))
    > + wrmsrl(MSR_KVM_EOI_EN, 0);
    > + kvm_pv_disable_apf();
    > +}
    > +
    > static int kvm_pv_reboot_notify(struct notifier_block *nb,
    > unsigned long code, void *unused)
    > {
    > if (code == SYS_RESTART)
    > - on_each_cpu(kvm_pv_disable_apf, NULL, 1);
    > + on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
    > return NOTIFY_DONE;
    > }
    >
    > @@ -378,7 +414,9 @@ static void __cpuinit kvm_guest_cpu_online(void *dummy)
    > static void kvm_guest_cpu_offline(void *dummy)
    > {
    > kvm_disable_steal_time();
    > - kvm_pv_disable_apf(NULL);
    > + if (kvm_para_has_feature(KVM_FEATURE_EOI))
    > + wrmsrl(MSR_KVM_EOI_EN, 0);
    > + kvm_pv_disable_apf();
    > apf_task_wake_all();
    > }
    >
    > @@ -431,6 +469,13 @@ void __init kvm_guest_init(void)
    > pv_time_ops.steal_clock = kvm_steal_clock;
    > }
    >
    > + if (kvm_para_has_feature(KVM_FEATURE_EOI)) {
    > + /* Should happen once after apic is initialized */
    > + BUG_ON(!apic);
    What if kernel was started with noapic?

    > + BUG_ON(apic->eoi_write == kvm_guest_apic_eoi_write);
    > + apic->eoi_write = kvm_guest_apic_eoi_write;
    > + }
    > +
    > #ifdef CONFIG_SMP
    > smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
    > register_cpu_notifier(&kvm_cpu_notifier);
    > --
    > 1.7.9.111.gf3fb0

    --
    Gleb.


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