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Date: Tue, 01 Nov 2011 14:34:27 -0500
From: Anthony Liguori <aliguori@...ibm.com>
To: Eric B Munson <emunson@...bm.net>
CC: avi@...hat.com, mingo@...hat.com, x86@...nel.org, hpa@...or.com,
arnd@...db.de, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
linux-arch@...r.kernel.org, ryanh@...ux.vnet.ibm.com
Subject: Re: [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@...bm.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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