linux-kernel - Re: [PATCH 6/6] KVM: X86: Implement userspace interface to set virtual_tsc

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Message-ID: <20110221171712.GC16508@amd.com>
Date:	Mon, 21 Feb 2011 18:17:13 +0100
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Zachary Amsden <zamsden@...hat.com>
Subject: Re: [PATCH 6/6] KVM: X86: Implement userspace interface to set
 virtual_tsc_khz

On Sun, Feb 13, 2011 at 10:12:14AM -0500, Avi Kivity wrote:
> On 02/09/2011 07:29 PM, Joerg Roedel wrote:
> > This patch implements two new vm-ioctls to get and set the
> > virtual_tsc_khz if the machine supports tsc-scaling. Setting
> > the tsc-frequency is only possible before userspace creates
> > any vcpu.
> >
> > Signed-off-by: Joerg Roedel<joerg.roedel@....com>
> > ---
> >   arch/x86/include/asm/kvm_host.h |    1 +
> >   arch/x86/kvm/svm.c              |    3 +++
> >   arch/x86/kvm/x86.c              |   38 ++++++++++++++++++++++++++++++++++++++
> >   include/linux/kvm.h             |    4 ++++
> >   4 files changed, 46 insertions(+), 0 deletions(-)
> >
> 
> Documentation/kvm/api.txt +++++++++++++
> 
> > @@ -633,6 +633,7 @@ 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);
> >
> >   extern bool tdp_enabled;
> > +extern int kvm_has_tsc_control;
> 
> bool
> 
> 
> > +	case KVM_SET_TSC_KHZ: {
> > +		u32 user_tsc_khz;
> > +
> > +		if (!kvm_has_tsc_control)
> > +			break;
> > +
> > +		/*
> > +		 * We force the tsc frequency to be set before any
> > +		 * vcpu is created
> > +		 */
> > +		if (atomic_read(&kvm->online_vcpus)>  0)
> > +			goto out;
> 
> What if a vcpu is created here?  No locking AFAICS.
> 
> > +
> > +		user_tsc_khz = arg;
> > +
> > +		kvm_arch_set_tsc_khz(kvm, user_tsc_khz);
> > +
> 
> Error check for impossible values (0, values the tsc multiplier can't 
> reach)?
> 
> > +		r = 0;
> > +		goto out;
> > +	}
> > +	case KVM_GET_TSC_KHZ: {
> > +
> > +		if (!kvm_has_tsc_control)
> > +			break;
> > +
> > +		r = -EFAULT;
> > +		if (copy_to_user(argp,&kvm->arch.virtual_tsc_khz, sizeof(__u32)))
> > +			goto out;
> 
> Should be the return value, no?
> 
> > +
> > +		r = 0;
> > +		goto out;
> > +	}
> >
> >   	default:
> >   		;
> >
> >
> > @@ -677,6 +678,9 @@ 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_TSC_CONTROL */
> > +#define KVM_SET_TSC_KHZ           _IOW(KVMIO,  0xa2, __u32)
> > +#define KVM_GET_TSC_KHZ           _IOR(KVMIO,  0xa3, __u32)
> >   
> 
> _IO() - use arg or return value
> _IOW/_IOR - copy_to/from_user()
> 
> pick one, but don't mix.

Thanks, I'll fix these issued in the next version.

Regards,

	Joerg

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