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    SubjectRe: [PATCH 6/6 V3] Add age out of guest paused flag
    On Fri, Nov 04, 2011 at 12:55:12PM -0400, 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>
    > Cc: mingo@redhat.com
    > Cc: hpa@zytor.com
    > Cc: arnd@arndb.de
    > Cc: ryanh@linux.vnet.ibm.com
    > Cc: aliguori@us.ibm.com
    > Cc: mtosatti@redhat.com
    > Cc: jeremy.fitzhardinge@citrix.com
    > Cc: kvm@vger.kernel.org
    > Cc: linux-arch@vger.kernel.org
    > Cc: x86@kernel.org
    > Cc: linux-kernel@vger.kernel.org
    > ---
    > Changes from V2:
    > Move function definition to kvm_host.h
    >
    > arch/x86/include/asm/kvm_host.h | 1 +
    > arch/x86/kvm/x86.c | 32 ++++++++++++++++++++++++++++++++
    > include/linux/kvm.h | 2 ++
    > include/linux/kvm_host.h | 2 ++
    > 4 files changed, 37 insertions(+), 0 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
    > index beb94c6..5cec925 100644
    > --- a/arch/x86/include/asm/kvm_host.h
    > +++ b/arch/x86/include/asm/kvm_host.h
    > @@ -673,6 +673,7 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long bytes,
    > u8 kvm_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn);
    >
    > int kvm_set_guest_paused(struct kvm_vcpu *vcpu);
    > +void kvm_clear_guest_paused(struct kvm_vcpu *vcpu, unsigned int length);
    >
    > extern bool tdp_enabled;
    >
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index 0127617..ca2187b 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"
    > @@ -3299,6 +3300,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
    > r = kvm_set_guest_paused(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;
    > }
    > @@ -6137,6 +6147,28 @@ int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
    > }
    > EXPORT_SYMBOL_GPL(kvm_set_guest_paused);
    >
    > +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);
    > +

    How about setting guest stopped flag when the guest is resumed, and
    clearing that flag on the guests watchdog timer interrupt (irrespective
    of whether a softlockup has been detected or not) ?

    Then this timer is not necessary.

    Unrelated: patch 3 is missing on the series, and please post functional
    and tested qemu-kvm patches along next time.

    Thanks.



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