Re: [KVM timekeeping 30/35] IOCTL for setting TSC rate

[Arnd Bergmann]

On Friday 20 August 2010 19:56:20 Glauber Costa wrote:
  @@ -675,6 +676,9 @@ struct kvm_clock_data {
   #define KVM_SET_PIT2  _IOW(KVMIO,  0xa0, struct kvm_pit_state2)
   /* Available with KVM_CAP_PPC_GET_PVINFO */
   #define KVM_PPC_GET_PVINFO _IOW(KVMIO,  0xa1, struct kvm_ppc_pvinfo)
  +/* Available with KVM_CAP_SET_TSC_RATE */
  +#define KVM_X86_GET_TSC_RATE  _IOR(KVMIO,  0xa2, __u32)
  +#define KVM_X86_SET_TSC_RATE  _IOW(KVMIO,  0xa3, __u32)
 
 wrap this into a struct?

I don't think that would improve the code. Generally, we try to *avoid* using
structs in ioctl arguments, although KVM does have a precedent of using structs
there.

In fact, the code here could be simplified by using get_user/put_user on the
simple argument, which would not be possibly with a struct.

Arnd
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[KVM timekeeping 30/35] IOCTL for setting TSC rate

[Zachary Amsden]

Add an IOCTL for setting the TSC rate for a VM, intended to
be used to migrate non-kvmclock based VMs which rely on TSC
rate staying stable across host migration.

Signed-off-by: Zachary Amsden zams...@redhat.com
---
 arch/x86/kvm/x86.c  |   36 
 include/linux/kvm.h |4 
 2 files changed, 40 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 887e30f..e618265 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1017,6 +1017,10 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
kvm_x86_ops-adjust_tsc_offset(v, tsc-tsc_timestamp);
local_irq_restore(flags);
 
+   /* hw_tsc_khz unknown at creation time, check for overrun */
+   if (this_tsc_khz  v-kvm-arch.virtual_tsc_khz)
+   vcpu-tsc_overrun = 1;
+
/* Now, see if we need to switch into trap mode */
if (vcpu-tsc_overrun  !vcpu-tsc_trapping)
kvm_x86_ops-set_tsc_trap(v, 1);
@@ -1846,6 +1850,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_DEBUGREGS:
case KVM_CAP_X86_ROBUST_SINGLESTEP:
case KVM_CAP_XSAVE:
+   case KVM_CAP_SET_TSC_RATE:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
@@ -3413,6 +3418,37 @@ long kvm_arch_vm_ioctl(struct file *filp,
r = 0;
break;
}
+   case KVM_X86_GET_TSC_RATE: {
+   u32 rate = kvm-arch.virtual_tsc_khz;
+   r = -EFAULT;
+   if (copy_to_user(argp, rate, sizeof(rate)))
+   goto out;
+   r = 0;
+   break;
+   }
+   case KVM_X86_SET_TSC_RATE: {
+   u32 rate;
+   int i;
+   struct kvm_vcpu *vcpu;
+   r = -EFAULT;
+   if (copy_from_user(rate, argp, sizeof rate))
+   goto out;
+   if (rate == 0 || rate  (1ULL  40)) {
+   r = -EINVAL;
+   break;
+   }
+   /*
+* This is intended to be called once, during VM creation.
+* Calling this with running VCPUs to dynamically change
+* speed is risky; there is no synchronization with the
+* compensation loop, so computations using virtual_tsc_khz
+* conversions may go haywire.  Use at your own risk.
+*/
+   kvm_arch_set_tsc_khz(kvm, rate);
+   kvm_for_each_vcpu(i, vcpu, kvm)
+   kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+   break;
+   }
 
default:
;
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 3707704..22d27f2 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -539,6 +539,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_XCRS 56
 #endif
 #define KVM_CAP_PPC_GET_PVINFO 57
+#define KVM_CAP_SET_TSC_RATE 58
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -675,6 +676,9 @@ struct kvm_clock_data {
 #define KVM_SET_PIT2  _IOW(KVMIO,  0xa0, struct kvm_pit_state2)
 /* Available with KVM_CAP_PPC_GET_PVINFO */
 #define KVM_PPC_GET_PVINFO   _IOW(KVMIO,  0xa1, struct kvm_ppc_pvinfo)
+/* Available with KVM_CAP_SET_TSC_RATE */
+#define KVM_X86_GET_TSC_RATE  _IOR(KVMIO,  0xa2, __u32)
+#define KVM_X86_SET_TSC_RATE  _IOW(KVMIO,  0xa3, __u32)
 
 /*
  * ioctls for vcpu fds
-- 
1.7.1

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Re: [KVM timekeeping 30/35] IOCTL for setting TSC rate

[Glauber Costa]

On Thu, Aug 19, 2010 at 10:07:44PM -1000, Zachary Amsden wrote:
 Add an IOCTL for setting the TSC rate for a VM, intended to
 be used to migrate non-kvmclock based VMs which rely on TSC
 rate staying stable across host migration.
 
 Signed-off-by: Zachary Amsden zams...@redhat.com
 ---
  arch/x86/kvm/x86.c  |   36 
  include/linux/kvm.h |4 
  2 files changed, 40 insertions(+), 0 deletions(-)
 
 diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
 index 887e30f..e618265 100644
 --- a/arch/x86/kvm/x86.c
 +++ b/arch/x86/kvm/x86.c
 @@ -1017,6 +1017,10 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
   kvm_x86_ops-adjust_tsc_offset(v, tsc-tsc_timestamp);
   local_irq_restore(flags);
  
 + /* hw_tsc_khz unknown at creation time, check for overrun */
 + if (this_tsc_khz  v-kvm-arch.virtual_tsc_khz)
 + vcpu-tsc_overrun = 1;
 +
   /* Now, see if we need to switch into trap mode */
   if (vcpu-tsc_overrun  !vcpu-tsc_trapping)
   kvm_x86_ops-set_tsc_trap(v, 1);
 @@ -1846,6 +1850,7 @@ int kvm_dev_ioctl_check_extension(long ext)
   case KVM_CAP_DEBUGREGS:
   case KVM_CAP_X86_ROBUST_SINGLESTEP:
   case KVM_CAP_XSAVE:
 + case KVM_CAP_SET_TSC_RATE:
   r = 1;
   break;
   case KVM_CAP_COALESCED_MMIO:
 @@ -3413,6 +3418,37 @@ long kvm_arch_vm_ioctl(struct file *filp,
   r = 0;
   break;
   }
 + case KVM_X86_GET_TSC_RATE: {
 + u32 rate = kvm-arch.virtual_tsc_khz;
 + r = -EFAULT;
 + if (copy_to_user(argp, rate, sizeof(rate)))
 + goto out;
 + r = 0;
 + break;
 + }
 + case KVM_X86_SET_TSC_RATE: {
 + u32 rate;
 + int i;
 + struct kvm_vcpu *vcpu;
 + r = -EFAULT;
 + if (copy_from_user(rate, argp, sizeof rate))
 + goto out;
 + if (rate == 0 || rate  (1ULL  40)) {
 + r = -EINVAL;
 + break;
 + }
 + /*
 +  * This is intended to be called once, during VM creation.
 +  * Calling this with running VCPUs to dynamically change
 +  * speed is risky; there is no synchronization with the
 +  * compensation loop, so computations using virtual_tsc_khz
 +  * conversions may go haywire.  Use at your own risk.
 +  */
 + kvm_arch_set_tsc_khz(kvm, rate);
 + kvm_for_each_vcpu(i, vcpu, kvm)
 + kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 + break;
 + }
  
   default:
   ;
 diff --git a/include/linux/kvm.h b/include/linux/kvm.h
 index 3707704..22d27f2 100644
 --- a/include/linux/kvm.h
 +++ b/include/linux/kvm.h
 @@ -539,6 +539,7 @@ struct kvm_ppc_pvinfo {
  #define KVM_CAP_XCRS 56
  #endif
  #define KVM_CAP_PPC_GET_PVINFO 57
 +#define KVM_CAP_SET_TSC_RATE 58
  
  #ifdef KVM_CAP_IRQ_ROUTING
  
 @@ -675,6 +676,9 @@ struct kvm_clock_data {
  #define KVM_SET_PIT2  _IOW(KVMIO,  0xa0, struct kvm_pit_state2)
  /* Available with KVM_CAP_PPC_GET_PVINFO */
  #define KVM_PPC_GET_PVINFO _IOW(KVMIO,  0xa1, struct kvm_ppc_pvinfo)
 +/* Available with KVM_CAP_SET_TSC_RATE */
 +#define KVM_X86_GET_TSC_RATE  _IOR(KVMIO,  0xa2, __u32)
 +#define KVM_X86_SET_TSC_RATE  _IOW(KVMIO,  0xa3, __u32)

wrap this into a struct?

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