Re: [PATCH v5 07/10] kvm: s390: Add CPU dump functionality

From: Janosch Frank <frankja@linux.ibm.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org,
	borntraeger@linux.ibm.com
Subject: Re: [PATCH v5 07/10] kvm: s390: Add CPU dump functionality
Date: Tue, 17 May 2022 15:42:18 +0200	[thread overview]
Message-ID: <0cf0234a-4ef5-3d08-ac80-afde1473fff7@linux.ibm.com> (raw)
In-Reply-To: <20220517133240.28f188c0@p-imbrenda>

On 5/17/22 13:32, Claudio Imbrenda wrote:
> On Mon, 16 May 2022 09:08:14 +0000
> Janosch Frank <frankja@linux.ibm.com> wrote:
> 
>> The previous patch introduced the per-VM dump functions now let's
>> focus on dumping the VCPU state via the newly introduced
>> KVM_S390_PV_CPU_COMMAND ioctl which mirrors the VM UV ioctl and can be
>> extended with new commands later.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>   arch/s390/kvm/kvm-s390.c | 73 ++++++++++++++++++++++++++++++++++++++++
>>   arch/s390/kvm/kvm-s390.h |  1 +
>>   arch/s390/kvm/pv.c       | 16 +++++++++
>>   include/uapi/linux/kvm.h |  4 +++
>>   4 files changed, 94 insertions(+)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 6bf9dd85d50f..c0c848c84552 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -5129,6 +5129,52 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
>>   	return -ENOIOCTLCMD;
>>   }
>>   
>> +static int kvm_s390_handle_pv_vcpu_dump(struct kvm_vcpu *vcpu,
>> +					struct kvm_pv_cmd *cmd)
>> +{
>> +	struct kvm_s390_pv_dmp dmp;
>> +	void *data;
>> +	int ret;
>> +
>> +	/* Dump initialization is a prerequisite */
>> +	if (!vcpu->kvm->arch.pv.dumping)
>> +		return -EINVAL;
>> +
>> +	if (copy_from_user(&dmp, (__u8 __user *)cmd->data, sizeof(dmp)))
>> +		return -EFAULT;
>> +
>> +	/* We only handle this subcmd right now */
>> +	if (dmp.subcmd != KVM_PV_DUMP_CPU)
>> +		return -EINVAL;
>> +
>> +	/* CPU dump length is the same as create cpu storage donation. */
>> +	if (dmp.buff_len != uv_info.guest_cpu_stor_len)
>> +		return -EINVAL;
>> +
>> +	data = vzalloc(uv_info.guest_cpu_stor_len);
> 
> is it really so big that you need to do a virtual allocation?
> (I thought it was at most a few pages)

It's at least a page

> 
> can you at least use kvzalloc?

Sure

> 
>> +	if (!data)
>> +		return -ENOMEM;
>> +
>> +	ret = kvm_s390_pv_dump_cpu(vcpu, data, &cmd->rc, &cmd->rrc);
>> +
>> +	VCPU_EVENT(vcpu, 3, "PROTVIRT DUMP CPU %d rc %x rrc %x",
>> +		   vcpu->vcpu_id, cmd->rc, cmd->rrc);
>> +
>> +	if (ret) {
>> +		vfree(data);
>> +		return -EINVAL;
> 
> if (ret)
> 	ret = -EINVAL;
> 
>> +	}
>> +
>> +	/* On success copy over the dump data */
>> +	if (copy_to_user((__u8 __user *)dmp.buff_addr, data, uv_info.guest_cpu_stor_len)) {
> 
> if (!ret && ...)
> 	ret = -EFAULT;
> 
>> +		vfree(data);
>> +		return -EFAULT;
>> +	}
>> +
>> +	vfree(data);
>> +	return 0;
> 
> return ret;
> 
> 
> this way you have only one free and one return, should be more readable
> 
>> +}
>> +
>>   long kvm_arch_vcpu_ioctl(struct file *filp,
>>   			 unsigned int ioctl, unsigned long arg)
>>   {
>> @@ -5293,6 +5339,33 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>>   					   irq_state.len);
>>   		break;
>>   	}
>> +	case KVM_S390_PV_CPU_COMMAND: {
>> +		struct kvm_pv_cmd cmd;
>> +
>> +		r = -EINVAL;
>> +		if (!is_prot_virt_host())
>> +			break;
>> +
>> +		r = -EFAULT;
>> +		if (copy_from_user(&cmd, argp, sizeof(cmd)))
>> +			break;
>> +
>> +		r = -EINVAL;
>> +		if (cmd.flags)
>> +			break;
>> +
>> +		/* We only handle this cmd right now */
>> +		if (cmd.cmd != KVM_PV_DUMP)
>> +			break;
>> +
>> +		r = kvm_s390_handle_pv_vcpu_dump(vcpu, &cmd);
>> +
>> +		/* Always copy over UV rc / rrc data */
>> +		if (copy_to_user((__u8 __user *)argp, &cmd.rc,
>> +				 sizeof(cmd.rc) + sizeof(cmd.rrc)))
>> +			r = -EFAULT;
>> +		break;
>> +	}
>>   	default:
>>   		r = -ENOTTY;
>>   	}
>> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
>> index 2868dd0bba25..a39815184350 100644
>> --- a/arch/s390/kvm/kvm-s390.h
>> +++ b/arch/s390/kvm/kvm-s390.h
>> @@ -250,6 +250,7 @@ int kvm_s390_pv_set_sec_parms(struct kvm *kvm, void *hdr, u64 length, u16 *rc,
>>   int kvm_s390_pv_unpack(struct kvm *kvm, unsigned long addr, unsigned long size,
>>   		       unsigned long tweak, u16 *rc, u16 *rrc);
>>   int kvm_s390_pv_set_cpu_state(struct kvm_vcpu *vcpu, u8 state);
>> +int kvm_s390_pv_dump_cpu(struct kvm_vcpu *vcpu, void *buff, u16 *rc, u16 *rrc);
>>   int kvm_s390_pv_dump_stor_state(struct kvm *kvm, void __user *buff_user,
>>   				u64 *gaddr, u64 buff_user_len, u16 *rc, u16 *rrc);
>>   
>> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
>> index fd261667d2c2..8c72330efc0e 100644
>> --- a/arch/s390/kvm/pv.c
>> +++ b/arch/s390/kvm/pv.c
>> @@ -300,6 +300,22 @@ int kvm_s390_pv_set_cpu_state(struct kvm_vcpu *vcpu, u8 state)
>>   	return 0;
>>   }
>>   
>> +int kvm_s390_pv_dump_cpu(struct kvm_vcpu *vcpu, void *buff, u16 *rc, u16 *rrc)
>> +{
>> +	struct uv_cb_dump_cpu uvcb = {
>> +		.header.cmd = UVC_CMD_DUMP_CPU,
>> +		.header.len = sizeof(uvcb),
>> +		.cpu_handle = vcpu->arch.pv.handle,
>> +		.dump_area_origin = (u64)buff,
>> +	};
>> +	int cc;
>> +
>> +	cc = uv_call_sched(0, (u64)&uvcb);
>> +	*rc = uvcb.header.rc;
>> +	*rrc = uvcb.header.rrc;
>> +	return cc;
>> +}
>> +
>>   /* Size of the cache for the storage state dump data. 1MB for now */
>>   #define DUMP_BUFF_LEN HPAGE_SIZE
>>   
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 1c60c2d314ba..0a8b57654ea7 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1657,6 +1657,7 @@ enum pv_cmd_dmp_id {
>>   	KVM_PV_DUMP_INIT,
>>   	KVM_PV_DUMP_CONFIG_STOR_STATE,
>>   	KVM_PV_DUMP_COMPLETE,
>> +	KVM_PV_DUMP_CPU,
>>   };
>>   
>>   struct kvm_s390_pv_dmp {
>> @@ -2118,4 +2119,7 @@ struct kvm_stats_desc {
>>   /* Available with KVM_CAP_XSAVE2 */
>>   #define KVM_GET_XSAVE2		  _IOR(KVMIO,  0xcf, struct kvm_xsave)
>>   
>> +/* Available with KVM_CAP_S390_PROTECTED_DUMP */
>> +#define KVM_S390_PV_CPU_COMMAND	_IOWR(KVMIO, 0xd0, struct kvm_pv_cmd)
>> +
>>   #endif /* __LINUX_KVM_H */
>