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    SubjectRe: [PATCH 6/6 V2] Add age out of guest paused flag
    On 10/31/2011 03:07 PM, Eric B Munson wrote:
    > The KVM_GUEST_PAUSED flag will prevent a guest from compaining about a soft
    > lockup but it can mask real soft lockups if the flag isn't cleared when it is
    > no longer relevant. This patch adds a kvm ioctl that the hypervisor will use
    > when it resumes a guest to start a timer for aging out the flag. The time out
    > will be specified by the hypervisor in the ioctl call.
    >
    > Signed-off-by: Eric B Munson<emunson@mgebm.net>

    Why not have the guest clear the flag when it acknowledges it?

    The hypervisor would unconditionally set the bit, and the guest would do a
    testandclear to check if the bit is set. I think that avoids the whole aging
    business.

    Regards,

    Anthony Liguori

    > ---
    > Cahnges from V1:
    > Add host functions for flag management to arch/x86/kvm/x86.c instead of
    > kvmclock.c
    >
    > arch/x86/include/asm/pvclock.h | 2 ++
    > arch/x86/kvm/x86.c | 32 ++++++++++++++++++++++++++++++++
    > include/linux/kvm.h | 2 ++
    > include/linux/kvm_host.h | 2 ++
    > 4 files changed, 38 insertions(+), 0 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
    > index 9312814..e8460b9 100644
    > --- a/arch/x86/include/asm/pvclock.h
    > +++ b/arch/x86/include/asm/pvclock.h
    > @@ -18,6 +18,8 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu);
    >
    > bool kvm_check_and_clear_host_stopped(int cpu);
    >
    > +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length);
    > +
    > /*
    > * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
    > * yielding a 64-bit result.
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index 592ac3b..fb0132a 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -46,6 +46,7 @@
    > #include<linux/hash.h>
    > #include<linux/pci.h>
    > #include<trace/events/kvm.h>
    > +#include<linux/timer.h>
    >
    > #define CREATE_TRACE_POINTS
    > #include "trace.h"
    > @@ -3300,6 +3301,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
    > kvm_set_host_stopped(vcpu);
    > break;
    > }
    > + case KVM_CLEAR_GUEST_PAUSED: {
    > + unsigned int length;
    > + r = -EFAULT;
    > + if (copy_from_user(&length, argp, sizeof length))
    > + goto out;
    > + r = 0;
    > + kvm_clear_guest_paused(vcpu, length);
    > + break;
    > + }
    > default:
    > r = -EINVAL;
    > }
    > @@ -6133,6 +6143,28 @@ void kvm_set_host_stopped(struct kvm_vcpu *vcpu)
    > }
    > EXPORT_SYMBOL_GPL(kvm_set_host_stopped);
    >
    > +static void kvm_timer_clear_guest_paused(unsigned long vcpu_addr)
    > +{
    > + struct kvm_vcpu *vcpu = (struct kvm_vcpu *)vcpu_addr;
    > + struct pvclock_vcpu_time_info *src =&vcpu->arch.hv_clock;
    > + src->flags = src->flags& (~PVCLOCK_GUEST_STOPPED);
    > +}
    > +
    > +/*
    > + * Host has resumed the guest, we need to clear the guest paused flag so we
    > + * don't mask any real soft lockups.
    > + */
    > +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length)
    > +{
    > + if (!timer_pending(&vcpu->flag_timer))
    > + setup_timer(&vcpu->flag_timer,
    > + kvm_timer_clear_guest_paused,
    > + (unsigned long)vcpu);
    > + mod_timer(&vcpu->flag_timer,
    > + jiffies + (length * HZ));
    > +}
    > +EXPORT_SYMBOL_GPL(kvm_clear_guest_paused);
    > +
    > int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
    > struct kvm_sregs *sregs)
    > {
    > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
    > index 87cab0d..bd9724c 100644
    > --- a/include/linux/kvm.h
    > +++ b/include/linux/kvm.h
    > @@ -765,6 +765,8 @@ struct kvm_clock_data {
    > #define KVM_ALLOCATE_RMA _IOR(KVMIO, 0xa9, struct kvm_allocate_rma)
    > /* VM is being stopped by host */
    > #define KVM_GUEST_PAUSED _IO(KVMIO, 0xaa)
    > +/* Start the timer to clear the paused flag */
    > +#define KVM_CLEAR_GUEST_PAUSED _IO(KVMIO, 0xab)
    >
    > #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1<< 0)
    >
    > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    > index d526231..043af4d 100644
    > --- a/include/linux/kvm_host.h
    > +++ b/include/linux/kvm_host.h
    > @@ -19,6 +19,7 @@
    > #include<linux/slab.h>
    > #include<linux/rcupdate.h>
    > #include<linux/ratelimit.h>
    > +#include<linux/timer.h>
    > #include<asm/signal.h>
    >
    > #include<linux/kvm.h>
    > @@ -154,6 +155,7 @@ struct kvm_vcpu {
    > #endif
    >
    > struct kvm_vcpu_arch arch;
    > + struct timer_list flag_timer;
    > };
    >
    > static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)



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