linux-kernel - Re: [PATCH 5/9] KVM: selftests: Align memory region addresses to 1M on s390x

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Date:   Fri, 24 May 2019 20:17:43 +0200
From:   Thomas Huth <thuth@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Andrew Jones <drjones@...hat.com>
Cc:     Janosch Frank <frankja@...ux.ibm.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH 5/9] KVM: selftests: Align memory region addresses to 1M
 on s390x

On 24/05/2019 10.29, Christian Borntraeger wrote:
> 
> 
> On 23.05.19 19:40, Andrew Jones wrote:
>> On Thu, May 23, 2019 at 06:43:05PM +0200, Thomas Huth wrote:
>>> On s390x, there is a constraint that memory regions have to be aligned
>>> to 1M (or running the VM will fail). Introduce a new "alignment" variable
>>> in the vm_userspace_mem_region_add() function which now can be used for
>>> both, huge page and s390x alignment requirements.
>>>
>>> Signed-off-by: Thomas Huth <thuth@...hat.com>
>>> ---
>>>  tools/testing/selftests/kvm/lib/kvm_util.c | 21 ++++++++++++++++-----
>>>  1 file changed, 16 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
>>> index 08edb8436c47..656df9d5cd4d 100644
>>> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
>>> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
>>> @@ -559,6 +559,7 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>>>  	unsigned long pmem_size = 0;
>>>  	struct userspace_mem_region *region;
>>>  	size_t huge_page_size = KVM_UTIL_PGS_PER_HUGEPG * vm->page_size;
>>> +	size_t alignment;
>>>  
>>>  	TEST_ASSERT((guest_paddr % vm->page_size) == 0, "Guest physical "
>>>  		"address not on a page boundary.\n"
>>> @@ -608,9 +609,20 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>>>  	TEST_ASSERT(region != NULL, "Insufficient Memory");
>>>  	region->mmap_size = npages * vm->page_size;
>>>  
>>> -	/* Enough memory to align up to a huge page. */
>>> +#ifdef __s390x__
>>> +	/* On s390x, the host address must be aligned to 1M (due to PGSTEs) */
>>> +	alignment = 0x100000;
>>> +#else
>>> +	alignment = 1;
>>> +#endif
>>> +
>>>  	if (src_type == VM_MEM_SRC_ANONYMOUS_THP)
>>> -		region->mmap_size += huge_page_size;
>>> +		alignment = huge_page_size;
>>
>> I guess s390x won't ever support VM_MEM_SRC_ANONYMOUS_THP? If it does,
>> then we need 'alignment = max(huge_page_size, alignment)'. Actually
>> that might be a nice way to write this anyway for future-proofing.
> 
> I can do 
> -		alignment = huge_page_size;
> +		alignment = max(huge_page_size, alignment);
> 
> when applying.

Yes, please, that's certainly cleaner this way.

 Thanks,
  Thomas