Re: [PATCH 3/5 V5] Add ioctl for KVMCLOCK_GUEST_STOPPED

[Eric B Munson]

On Wed, 07 Dec 2011, Avi Kivity wrote:

 On 12/05/2011 10:19 PM, Eric B Munson wrote:
  Now that we have a flag that will tell the guest it was suspended, create an
  interface for that communication using a KVM ioctl.
 
  @@ -3295,6 +3295,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
   
  goto out;
  }
  +   case KVMCLOCK_GUEST_PAUSED: {
  +   r = kvm_set_guest_paused(vcpu);
  +   break;
  +   }
  default:
  r = -EINVAL;
  }
 
 
 You could also do this purely from userspace by reading the kvmclock msr
 and updating it.  However, it's better to do this in the kernel to avoid
 distributing responsibility for kvmclock across too many cooks.
 
 -- 
 error compiling committee.c: too many arguments to function
 

As stated in the cover letter, per Marcelo's suggestion I already tried this
method and it resulted in the guest wall clock skewing by the amount of time
the guest was suspended.  This places a new burden on the guest to be running
ntpd or equivslent to keep the wall clock correct.

Eric


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Re: [PATCH 3/5 V5] Add ioctl for KVMCLOCK_GUEST_STOPPED

[Avi Kivity]

On 12/05/2011 10:19 PM, Eric B Munson wrote:
 Now that we have a flag that will tell the guest it was suspended, create an
 interface for that communication using a KVM ioctl.

 @@ -3295,6 +3295,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
  
   goto out;
   }
 + case KVMCLOCK_GUEST_PAUSED: {
 + r = kvm_set_guest_paused(vcpu);
 + break;
 + }
   default:
   r = -EINVAL;
   }


You could also do this purely from userspace by reading the kvmclock msr
and updating it.  However, it's better to do this in the kernel to avoid
distributing responsibility for kvmclock across too many cooks.

-- 
error compiling committee.c: too many arguments to function

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[PATCH 3/5 V5] Add ioctl for KVMCLOCK_GUEST_STOPPED

[Eric B Munson]

Now that we have a flag that will tell the guest it was suspended, create an
interface for that communication using a KVM ioctl.

Signed-off-by: Eric B Munson emun...@mgebm.net

Cc: mi...@redhat.com
Cc: h...@zytor.com
Cc: a...@arndb.de
Cc: ry...@linux.vnet.ibm.com
Cc: aligu...@us.ibm.com
Cc: mtosa...@redhat.com
Cc: jeremy.fitzhardi...@citrix.com
Cc: levinsasha...@gmail.com
Cc: Jan Kiszka jan.kis...@siemens.com
Cc: kvm@vger.kernel.org
Cc: linux-a...@vger.kernel.org
Cc: x...@kernel.org
Cc: linux-ker...@vger.kernel.org
---
Changes from V4:
 Rename KVM_GUEST_PAUSED to KVMCLOCK_GUEST_PAUSED
 Add new ioctl description to api.txt

 Documentation/virtual/kvm/api.txt |   12 
 arch/x86/include/asm/kvm_host.h   |2 ++
 arch/x86/kvm/x86.c|   20 
 include/linux/kvm.h   |2 ++
 4 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt 
b/Documentation/virtual/kvm/api.txt
index 7945b0b..0f7dd99 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1450,6 +1450,18 @@ is supported; 2 if the processor requires all virtual 
machines to have
 an RMA, or 1 if the processor can use an RMA but doesn't require it,
 because it supports the Virtual RMA (VRMA) facility.
 
+4.64 KVMCLOCK_GUEST_PAUSED
+
+Capability: basic
+Architechtures: Any that implement pvclocks (currently x86 only)
+Type: vcpu ioctl
+Parameters: None
+Returns: 0 on success, -1 on error
+
+This signals to the host kernel that the specified guest is being paused by
+userspace.  The host will set a flag in the pvclock structure that is checked
+from the soft lockup watchdog.
+
 5. The kvm_run structure
 
 Application code obtains a pointer to the kvm_run structure by
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b4973f4..beb94c6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -672,6 +672,8 @@ int kvm_pv_mmu_op(struct kvm_vcpu *vcpu, unsigned long 
bytes,
  gpa_t addr, unsigned long *ret);
 u8 kvm_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn);
 
+int kvm_set_guest_paused(struct kvm_vcpu *vcpu);
+
 extern bool tdp_enabled;
 
 u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c38efd7..1dab5fd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3295,6 +3295,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 
goto out;
}
+   case KVMCLOCK_GUEST_PAUSED: {
+   r = kvm_set_guest_paused(vcpu);
+   break;
+   }
default:
r = -EINVAL;
}
@@ -6117,6 +6121,22 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 
tss_selector, int reason,
 }
 EXPORT_SYMBOL_GPL(kvm_task_switch);
 
+/*
+ * kvm_set_guest_paused() indicates to the guest kernel that it has been
+ * stopped by the hypervisor.  This function will be called from the host only.
+ * EINVAL is returned when the host attempts to set the flag for a guest that
+ * does not support pv clocks.
+ */
+int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
+{
+   struct pvclock_vcpu_time_info *src = vcpu-arch.hv_clock;
+   if (!vcpu-arch.time_page)
+   return -EINVAL;
+   src-flags |= PVCLOCK_GUEST_STOPPED;
+   return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_set_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 c3892fc..1d1ddef 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -762,6 +762,8 @@ struct kvm_clock_data {
 #define KVM_CREATE_SPAPR_TCE _IOW(KVMIO,  0xa8, struct 
kvm_create_spapr_tce)
 /* Available with KVM_CAP_RMA */
 #define KVM_ALLOCATE_RMA _IOR(KVMIO,  0xa9, struct kvm_allocate_rma)
+/* VM is being stopped by host */
+#define KVMCLOCK_GUEST_PAUSED_IO(KVMIO,   0xaa)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU(1  0)
 
-- 
1.7.5.4

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