linux-kernel - Re: [PATCH v10 2/3] KVM: s390: guest support for topology function

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Date:   Mon, 27 Jun 2022 19:40:25 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, cohuck@...hat.com, david@...hat.com,
        thuth@...hat.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        wintera@...ux.ibm.com, seiden@...ux.ibm.com, nrb@...ux.ibm.com
Subject: Re: [PATCH v10 2/3] KVM: s390: guest support for topology function



On 6/24/22 11:32, Claudio Imbrenda wrote:
> On Mon, 20 Jun 2022 14:54:36 +0200
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
> 
>> We report a topology change to the guest for any CPU hotplug.
>>
>> The reporting to the guest is done using the Multiprocessor
>> Topology-Change-Report (MTCR) bit of the utility entry in the guest's
>> SCA which will be cleared during the interpretation of PTF.
>>
>> On every vCPU creation we set the MCTR bit to let the guest know the
>> next time he uses the PTF with command 2 instruction that the
>> topology changed and that he should use the STSI(15.1.x) instruction
>> to get the topology details.
>>
>> STSI(15.1.x) gives information on the CPU configuration topology.
>> Let's accept the interception of STSI with the function code 15 and
>> let the userland part of the hypervisor handle it when userland
>> support the CPU Topology facility.
>>
>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h | 11 ++++++++---
>>   arch/s390/kvm/kvm-s390.c         | 27 ++++++++++++++++++++++++++-
>>   arch/s390/kvm/priv.c             | 15 +++++++++++----
>>   arch/s390/kvm/vsie.c             |  3 +++
>>   4 files changed, 48 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index 766028d54a3e..bb54196d4ed6 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -97,15 +97,19 @@ struct bsca_block {
>>   	union ipte_control ipte_control;
>>   	__u64	reserved[5];
>>   	__u64	mcn;
>> -	__u64	reserved2;
>> +#define SCA_UTILITY_MTCR	0x8000
>> +	__u16	utility;
>> +	__u8	reserved2[6];
>>   	struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
>>   };
>>   
>>   struct esca_block {
>>   	union ipte_control ipte_control;
>> -	__u64   reserved1[7];
>> +	__u64   reserved1[6];
>> +	__u16	utility;
>> +	__u8	reserved2[6];
>>   	__u64   mcn[4];
>> -	__u64   reserved2[20];
>> +	__u64   reserved3[20];
>>   	struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS];
>>   };
>>   
>> @@ -249,6 +253,7 @@ struct kvm_s390_sie_block {
>>   #define ECB_SPECI	0x08
>>   #define ECB_SRSI	0x04
>>   #define ECB_HOSTPROTINT	0x02
>> +#define ECB_PTF		0x01
>>   	__u8	ecb;			/* 0x0061 */
>>   #define ECB2_CMMA	0x80
>>   #define ECB2_IEP	0x20
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 8fcb56141689..95b96019ca8e 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
>>   	return ret;
>>   }
>>   
>> +/**
>> + * kvm_s390_sca_set_mtcr
> 
> the format for kdoc is:
> 
> 	function_name - very short description
> 
> please add a very short description. something like:
> 
> 	kvm_s390_sca_set_mtcr - update mtcr to signal topology change


OK, thanks,

Pierre

-- 
Pierre Morel
IBM Lab Boeblingen