diff mbox series

[v8,2/2] s390x: KVM: resetting the Topology-Change-Report

Message ID 20220420113430.11876-3-pmorel@linux.ibm.com (mailing list archive)
State New, archived
Headers show
Series s390x: KVM: CPU Topology | expand

Commit Message

Pierre Morel April 20, 2022, 11:34 a.m. UTC 
During a subsystem reset the Topology-Change-Report is cleared.
Let's give userland the possibility to clear the MTCR in the case
of a subsystem reset.

To migrate the MTCR, let's give userland the possibility to
query the MTCR state.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
---
 arch/s390/include/uapi/asm/kvm.h |   9 +++
 arch/s390/kvm/kvm-s390.c         | 103 +++++++++++++++++++++++++++++++
 2 files changed, 112 insertions(+)

Comments

kernel test robot April 21, 2022, 6:40 a.m. UTC | #1 
Hi Pierre,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kvm/master]
[also build test WARNING on v5.18-rc3]
[cannot apply to kvms390/next mst-vhost/linux-next next-20220420]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Pierre-Morel/s390x-KVM-CPU-Topology/20220420-194302
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git master
config: s390-randconfig-r044-20220420 (https://download.01.org/0day-ci/archive/20220420/202204202111.vLX6pMo0-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project bac6cd5bf85669e3376610cfc4c4f9ca015e7b9b)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install s390 cross compiling tool for clang build
        # apt-get install binutils-s390x-linux-gnu
        # https://github.com/intel-lab-lkp/linux/commit/0bdeef651636ac2ef4918fb6e3230614e2fb3581
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Pierre-Morel/s390x-KVM-CPU-Topology/20220420-194302
        git checkout 0bdeef651636ac2ef4918fb6e3230614e2fb3581
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash arch/s390/kvm/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from arch/s390/kvm/kvm-s390.c:22:
   In file included from include/linux/kvm_host.h:41:
   In file included from include/linux/kvm_para.h:5:
   In file included from include/uapi/linux/kvm_para.h:37:
   In file included from arch/s390/include/asm/kvm_para.h:25:
   In file included from arch/s390/include/asm/diag.h:12:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:10:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:75:
   include/asm-generic/io.h:464:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __raw_readb(PCI_IOBASE + addr);
                             ~~~~~~~~~~ ^
   include/asm-generic/io.h:477:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:37:59: note: expanded from macro '__le16_to_cpu'
   #define __le16_to_cpu(x) __swab16((__force __u16)(__le16)(x))
                                                             ^
   include/uapi/linux/swab.h:102:54: note: expanded from macro '__swab16'
   #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
                                                        ^
   In file included from arch/s390/kvm/kvm-s390.c:22:
   In file included from include/linux/kvm_host.h:41:
   In file included from include/linux/kvm_para.h:5:
   In file included from include/uapi/linux/kvm_para.h:37:
   In file included from arch/s390/include/asm/kvm_para.h:25:
   In file included from arch/s390/include/asm/diag.h:12:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:10:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:75:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:35:59: note: expanded from macro '__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:115:54: note: expanded from macro '__swab32'
   #define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
                                                        ^
   In file included from arch/s390/kvm/kvm-s390.c:22:
   In file included from include/linux/kvm_host.h:41:
   In file included from include/linux/kvm_para.h:5:
   In file included from include/uapi/linux/kvm_para.h:37:
   In file included from arch/s390/include/asm/kvm_para.h:25:
   In file included from arch/s390/include/asm/diag.h:12:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:10:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:75:
   include/asm-generic/io.h:501:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writeb(value, PCI_IOBASE + addr);
                               ~~~~~~~~~~ ^
   include/asm-generic/io.h:511:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:521:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:609:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsb(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:617:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsw(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:625:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsl(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:634:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesb(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   include/asm-generic/io.h:643:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesw(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   include/asm-generic/io.h:652:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesl(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
>> arch/s390/kvm/kvm-s390.c:1773:6: warning: variable 'val' set but not used [-Wunused-but-set-variable]
           int val;
               ^
   13 warnings generated.


vim +/val +1773 arch/s390/kvm/kvm-s390.c

  1758	
  1759	/**
  1760	 * kvm_s390_sca_clear_mtcr
  1761	 * @kvm: guest KVM description
  1762	 *
  1763	 * Is only relevant if the topology facility is present,
  1764	 * the caller should check KVM facility 11
  1765	 *
  1766	 * Updates the Multiprocessor Topology-Change-Report to signal
  1767	 * the guest with a topology change.
  1768	 */
  1769	static int kvm_s390_sca_clear_mtcr(struct kvm *kvm)
  1770	{
  1771		struct bsca_block *sca = kvm->arch.sca;
  1772		struct kvm_vcpu *vcpu;
> 1773		int val;
  1774	
  1775		vcpu = kvm_s390_get_first_vcpu(kvm);
  1776		if (!vcpu)
  1777			return -ENODEV;
  1778	
  1779		ipte_lock(vcpu);
  1780		val = READ_ONCE(sca->utility);
  1781		WRITE_ONCE(sca->utility, sca->utility & ~SCA_UTILITY_MTCR);
  1782		ipte_unlock(vcpu);
  1783	
  1784		return 0;
  1785	}
  1786
kernel test robot April 21, 2022, 6:41 a.m. UTC | #2 
Hi Pierre,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kvm/master]
[also build test WARNING on v5.18-rc3]
[cannot apply to kvms390/next mst-vhost/linux-next next-20220420]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Pierre-Morel/s390x-KVM-CPU-Topology/20220420-194302
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git master
config: s390-allyesconfig (https://download.01.org/0day-ci/archive/20220421/202204210249.JUYt00GG-lkp@intel.com/config)
compiler: s390-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/0bdeef651636ac2ef4918fb6e3230614e2fb3581
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Pierre-Morel/s390x-KVM-CPU-Topology/20220420-194302
        git checkout 0bdeef651636ac2ef4918fb6e3230614e2fb3581
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash arch/s390/kvm/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   arch/s390/kvm/kvm-s390.c: In function 'kvm_s390_sca_clear_mtcr':
>> arch/s390/kvm/kvm-s390.c:1773:13: warning: variable 'val' set but not used [-Wunused-but-set-variable]
    1773 |         int val;
         |             ^~~


vim +/val +1773 arch/s390/kvm/kvm-s390.c

  1758	
  1759	/**
  1760	 * kvm_s390_sca_clear_mtcr
  1761	 * @kvm: guest KVM description
  1762	 *
  1763	 * Is only relevant if the topology facility is present,
  1764	 * the caller should check KVM facility 11
  1765	 *
  1766	 * Updates the Multiprocessor Topology-Change-Report to signal
  1767	 * the guest with a topology change.
  1768	 */
  1769	static int kvm_s390_sca_clear_mtcr(struct kvm *kvm)
  1770	{
  1771		struct bsca_block *sca = kvm->arch.sca;
  1772		struct kvm_vcpu *vcpu;
> 1773		int val;
  1774	
  1775		vcpu = kvm_s390_get_first_vcpu(kvm);
  1776		if (!vcpu)
  1777			return -ENODEV;
  1778	
  1779		ipte_lock(vcpu);
  1780		val = READ_ONCE(sca->utility);
  1781		WRITE_ONCE(sca->utility, sca->utility & ~SCA_UTILITY_MTCR);
  1782		ipte_unlock(vcpu);
  1783	
  1784		return 0;
  1785	}
  1786
David Hildenbrand April 28, 2022, 1:50 p.m. UTC | #3 
On 20.04.22 13:34, Pierre Morel wrote:
> During a subsystem reset the Topology-Change-Report is cleared.
> Let's give userland the possibility to clear the MTCR in the case
> of a subsystem reset.
> 
> To migrate the MTCR, let's give userland the possibility to
> query the MTCR state.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  arch/s390/include/uapi/asm/kvm.h |   9 +++
>  arch/s390/kvm/kvm-s390.c         | 103 +++++++++++++++++++++++++++++++
>  2 files changed, 112 insertions(+)
> 
> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
> index 7a6b14874d65..bb3df6d49f27 100644
> --- a/arch/s390/include/uapi/asm/kvm.h
> +++ b/arch/s390/include/uapi/asm/kvm.h
> @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req {
>  #define KVM_S390_VM_CRYPTO		2
>  #define KVM_S390_VM_CPU_MODEL		3
>  #define KVM_S390_VM_MIGRATION		4
> +#define KVM_S390_VM_CPU_TOPOLOGY	5
>  
>  /* kvm attributes for mem_ctrl */
>  #define KVM_S390_VM_MEM_ENABLE_CMMA	0
> @@ -171,6 +172,14 @@ struct kvm_s390_vm_cpu_subfunc {
>  #define KVM_S390_VM_MIGRATION_START	1
>  #define KVM_S390_VM_MIGRATION_STATUS	2
>  
> +/* kvm attributes for cpu topology */
> +#define KVM_S390_VM_CPU_TOPO_MTR_CLEAR	0
> +#define KVM_S390_VM_CPU_TOPO_MTR_SET	1
> +
> +struct kvm_s390_cpu_topology {
> +	__u16 mtcr;
> +};

Just wondering:

1) Do we really need a struct for that
2) Do we want to leave some room for later expansion?

> +
>  /* for KVM_GET_REGS and KVM_SET_REGS */
>  struct kvm_regs {
>  	/* general purpose regs for s390 */
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 925ccc59f283..755f325c9e70 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1756,6 +1756,100 @@ static int kvm_s390_sca_set_mtcr(struct kvm *kvm)
>  	return 0;
>  }
>  
> +/**
> + * kvm_s390_sca_clear_mtcr
> + * @kvm: guest KVM description
> + *
> + * Is only relevant if the topology facility is present,
> + * the caller should check KVM facility 11
> + *
> + * Updates the Multiprocessor Topology-Change-Report to signal
> + * the guest with a topology change.
> + */
> +static int kvm_s390_sca_clear_mtcr(struct kvm *kvm)
> +{
> +	struct bsca_block *sca = kvm->arch.sca;
> +	struct kvm_vcpu *vcpu;
> +	int val;
> +
> +	vcpu = kvm_s390_get_first_vcpu(kvm);
> +	if (!vcpu)
> +		return -ENODEV;

It would be cleaner to have ipte_lock/ipte_unlock variants that are
independent of a vcpu.

Instead of checking for "vcpu->arch.sie_block->eca & ECA_SII" we might
just check for sclp.has_siif. Everything else that performs the
lock/unlock should be contained in "struct kvm" directly, unless I am
missing something.

[...]

> +
> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
> +{
> +	struct kvm_s390_cpu_topology *topology;
> +	int ret = 0;
> +
> +	if (!test_kvm_facility(kvm, 11))
> +		return -ENXIO;
> +
> +	topology = kzalloc(sizeof(*topology), GFP_KERNEL);
> +	if (!topology)
> +		return -ENOMEM;

I'm confused. We're allocating a __u16 to then free it again below? Why
not simply use a value on the stack like in kvm_s390_vm_get_migration()?



u16 mtcr;
...
mtcr = kvm_s390_sca_get_mtcr(kvm);

if (copy_to_user((void __user *)attr->addr, &mtcr, sizeof(mtcr)))
	return -EFAULT;
return 0;



> +
> +	topology->mtcr =  kvm_s390_sca_get_mtcr(kvm);

s/  / /

> +	if (copy_to_user((void __user *)attr->addr, topology,
> +			 sizeof(struct kvm_s390_cpu_topology)))
> +		ret = -EFAULT;
> +
> +	kfree(topology);
> +	return ret;
> +}
> +
Pierre Morel May 4, 2022, 8:05 a.m. UTC | #4 
On 4/28/22 15:50, David Hildenbrand wrote:
> On 20.04.22 13:34, Pierre Morel wrote:
>> During a subsystem reset the Topology-Change-Report is cleared.
>> Let's give userland the possibility to clear the MTCR in the case
>> of a subsystem reset.
>>
>> To migrate the MTCR, let's give userland the possibility to
>> query the MTCR state.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> ---
>>   arch/s390/include/uapi/asm/kvm.h |   9 +++
>>   arch/s390/kvm/kvm-s390.c         | 103 +++++++++++++++++++++++++++++++
>>   2 files changed, 112 insertions(+)
>>
>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>> index 7a6b14874d65..bb3df6d49f27 100644
>> --- a/arch/s390/include/uapi/asm/kvm.h
>> +++ b/arch/s390/include/uapi/asm/kvm.h
>> @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req {
>>   #define KVM_S390_VM_CRYPTO		2
>>   #define KVM_S390_VM_CPU_MODEL		3
>>   #define KVM_S390_VM_MIGRATION		4
>> +#define KVM_S390_VM_CPU_TOPOLOGY	5
>>   
>>   /* kvm attributes for mem_ctrl */
>>   #define KVM_S390_VM_MEM_ENABLE_CMMA	0
>> @@ -171,6 +172,14 @@ struct kvm_s390_vm_cpu_subfunc {
>>   #define KVM_S390_VM_MIGRATION_START	1
>>   #define KVM_S390_VM_MIGRATION_STATUS	2
>>   
>> +/* kvm attributes for cpu topology */
>> +#define KVM_S390_VM_CPU_TOPO_MTR_CLEAR	0
>> +#define KVM_S390_VM_CPU_TOPO_MTR_SET	1
>> +
>> +struct kvm_s390_cpu_topology {
>> +	__u16 mtcr;
>> +};
> 
> Just wondering:
> 
> 1) Do we really need a struct for that
> 2) Do we want to leave some room for later expansion?

Yes it is the goal, if we want to report more topology information for 
the case the vCPUs are not pin on the real CPUs.
In this case I think we need to report more information on the vCPU 
topology to the guest.
For now I explicitly limited the case to pinned vCPUs.

But the change from a u16 to a structure can be done at that moment.

> 
>> +
>>   /* for KVM_GET_REGS and KVM_SET_REGS */
>>   struct kvm_regs {
>>   	/* general purpose regs for s390 */
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 925ccc59f283..755f325c9e70 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -1756,6 +1756,100 @@ static int kvm_s390_sca_set_mtcr(struct kvm *kvm)
>>   	return 0;
>>   }
>>   
>> +/**
>> + * kvm_s390_sca_clear_mtcr
>> + * @kvm: guest KVM description
>> + *
>> + * Is only relevant if the topology facility is present,
>> + * the caller should check KVM facility 11
>> + *
>> + * Updates the Multiprocessor Topology-Change-Report to signal
>> + * the guest with a topology change.
>> + */
>> +static int kvm_s390_sca_clear_mtcr(struct kvm *kvm)
>> +{
>> +	struct bsca_block *sca = kvm->arch.sca;
>> +	struct kvm_vcpu *vcpu;
>> +	int val;
>> +
>> +	vcpu = kvm_s390_get_first_vcpu(kvm);
>> +	if (!vcpu)
>> +		return -ENODEV;
> 
> It would be cleaner to have ipte_lock/ipte_unlock variants that are
> independent of a vcpu.
> 
> Instead of checking for "vcpu->arch.sie_block->eca & ECA_SII" we might
> just check for sclp.has_siif. Everything else that performs the
> lock/unlock should be contained in "struct kvm" directly, unless I am
> missing something.

No you are right, ipte_lock/unlock are independent of the vcpu.
I already had a patch on this but I did not think about sclp.has_siif 
and it was still heavy.

> 
> [...]
> 
>> +
>> +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
>> +{
>> +	struct kvm_s390_cpu_topology *topology;
>> +	int ret = 0;
>> +
>> +	if (!test_kvm_facility(kvm, 11))
>> +		return -ENXIO;
>> +
>> +	topology = kzalloc(sizeof(*topology), GFP_KERNEL);
>> +	if (!topology)
>> +		return -ENOMEM;
> 
> I'm confused. We're allocating a __u16 to then free it again below? Why
> not simply use a value on the stack like in kvm_s390_vm_get_migration()?

comes from the idea to bring up more information.
But done like this it has no point.


> 
> 
> 
> u16 mtcr;
> ...
> mtcr = kvm_s390_sca_get_mtcr(kvm);
> 
> if (copy_to_user((void __user *)attr->addr, &mtcr, sizeof(mtcr)))
> 	return -EFAULT;
> return 0;

yes, thanks.

> 
> 
> 
>> +
>> +	topology->mtcr =  kvm_s390_sca_get_mtcr(kvm);
> 
> s/  / /

yes too

> 
>> +	if (copy_to_user((void __user *)attr->addr, topology,
>> +			 sizeof(struct kvm_s390_cpu_topology)))
>> +		ret = -EFAULT;
>> +
>> +	kfree(topology);
>> +	return ret;
>> +}
>> +
> 
> 


Thanks a lot David,

Regards,
Pierre
diff mbox series

Patch

diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
index 7a6b14874d65..bb3df6d49f27 100644
--- a/arch/s390/include/uapi/asm/kvm.h
+++ b/arch/s390/include/uapi/asm/kvm.h
@@ -74,6 +74,7 @@  struct kvm_s390_io_adapter_req {
 #define KVM_S390_VM_CRYPTO		2
 #define KVM_S390_VM_CPU_MODEL		3
 #define KVM_S390_VM_MIGRATION		4
+#define KVM_S390_VM_CPU_TOPOLOGY	5
 
 /* kvm attributes for mem_ctrl */
 #define KVM_S390_VM_MEM_ENABLE_CMMA	0
@@ -171,6 +172,14 @@  struct kvm_s390_vm_cpu_subfunc {
 #define KVM_S390_VM_MIGRATION_START	1
 #define KVM_S390_VM_MIGRATION_STATUS	2
 
+/* kvm attributes for cpu topology */
+#define KVM_S390_VM_CPU_TOPO_MTR_CLEAR	0
+#define KVM_S390_VM_CPU_TOPO_MTR_SET	1
+
+struct kvm_s390_cpu_topology {
+	__u16 mtcr;
+};
+
 /* for KVM_GET_REGS and KVM_SET_REGS */
 struct kvm_regs {
 	/* general purpose regs for s390 */
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 925ccc59f283..755f325c9e70 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1756,6 +1756,100 @@  static int kvm_s390_sca_set_mtcr(struct kvm *kvm)
 	return 0;
 }
 
+/**
+ * kvm_s390_sca_clear_mtcr
+ * @kvm: guest KVM description
+ *
+ * Is only relevant if the topology facility is present,
+ * the caller should check KVM facility 11
+ *
+ * Updates the Multiprocessor Topology-Change-Report to signal
+ * the guest with a topology change.
+ */
+static int kvm_s390_sca_clear_mtcr(struct kvm *kvm)
+{
+	struct bsca_block *sca = kvm->arch.sca;
+	struct kvm_vcpu *vcpu;
+	int val;
+
+	vcpu = kvm_s390_get_first_vcpu(kvm);
+	if (!vcpu)
+		return -ENODEV;
+
+	ipte_lock(vcpu);
+	val = READ_ONCE(sca->utility);
+	WRITE_ONCE(sca->utility, sca->utility & ~SCA_UTILITY_MTCR);
+	ipte_unlock(vcpu);
+
+	return 0;
+}
+
+/**
+ * kvm_s390_sca_get_mtcr
+ * @kvm: guest KVM description
+ *
+ * Is only relevant if the topology facility is present,
+ * the caller should check KVM facility 11
+ *
+ * reports to QEMU the Multiprocessor Topology-Change-Report.
+ */
+static int kvm_s390_sca_get_mtcr(struct kvm *kvm)
+{
+	struct bsca_block *sca = kvm->arch.sca;
+	struct kvm_vcpu *vcpu;
+	int val;
+
+	vcpu = kvm_s390_get_first_vcpu(kvm);
+	if (!vcpu)
+		return -ENODEV;
+
+	ipte_lock(vcpu);
+	val = READ_ONCE(sca->utility);
+	ipte_unlock(vcpu);
+
+	return val;
+}
+
+static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+	int ret = -EFAULT;
+
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
+	switch (attr->attr) {
+	case KVM_S390_VM_CPU_TOPO_MTR_SET:
+		ret = kvm_s390_sca_set_mtcr(kvm);
+		break;
+	case KVM_S390_VM_CPU_TOPO_MTR_CLEAR:
+		ret = kvm_s390_sca_clear_mtcr(kvm);
+		break;
+	}
+
+	return ret;
+}
+
+static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+	struct kvm_s390_cpu_topology *topology;
+	int ret = 0;
+
+	if (!test_kvm_facility(kvm, 11))
+		return -ENXIO;
+
+	topology = kzalloc(sizeof(*topology), GFP_KERNEL);
+	if (!topology)
+		return -ENOMEM;
+
+	topology->mtcr =  kvm_s390_sca_get_mtcr(kvm);
+	if (copy_to_user((void __user *)attr->addr, topology,
+			 sizeof(struct kvm_s390_cpu_topology)))
+		ret = -EFAULT;
+
+	kfree(topology);
+	return ret;
+}
+
 static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 {
 	int ret;
@@ -1776,6 +1870,9 @@  static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_MIGRATION:
 		ret = kvm_s390_vm_set_migration(kvm, attr);
 		break;
+	case KVM_S390_VM_CPU_TOPOLOGY:
+		ret = kvm_s390_set_topology(kvm, attr);
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1801,6 +1898,9 @@  static int kvm_s390_vm_get_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_MIGRATION:
 		ret = kvm_s390_vm_get_migration(kvm, attr);
 		break;
+	case KVM_S390_VM_CPU_TOPOLOGY:
+		ret = kvm_s390_get_topology(kvm, attr);
+		break;
 	default:
 		ret = -ENXIO;
 		break;
@@ -1874,6 +1974,9 @@  static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
 	case KVM_S390_VM_MIGRATION:
 		ret = 0;
 		break;
+	case KVM_S390_VM_CPU_TOPOLOGY:
+		ret = test_kvm_facility(kvm, 11) ? 0 : -ENXIO;
+		break;
 	default:
 		ret = -ENXIO;
 		break;