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

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Date:	Sun, 13 Feb 2011 17:12:14 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...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 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.

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

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