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

[Christian Borntraeger]

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@xxxxxxxxxx>
>> ---
>>  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.


> 
>> +
>> +	/* Add enough memory to align up if necessary */
>> +	if (alignment > 1)
>> +		region->mmap_size += alignment;
>> +
>>  	region->mmap_start = mmap(NULL, region->mmap_size,
>>  				  PROT_READ | PROT_WRITE,
>>  				  MAP_PRIVATE | MAP_ANONYMOUS
>> @@ -620,9 +632,8 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
>>  		    "test_malloc failed, mmap_start: %p errno: %i",
>>  		    region->mmap_start, errno);
>>  
>> -	/* Align THP allocation up to start of a huge page. */
>> -	region->host_mem = align(region->mmap_start,
>> -				 src_type == VM_MEM_SRC_ANONYMOUS_THP ?  huge_page_size : 1);
>> +	/* Align host address */
>> +	region->host_mem = align(region->mmap_start, alignment);
>>  
>>  	/* As needed perform madvise */
>>  	if (src_type == VM_MEM_SRC_ANONYMOUS || src_type == VM_MEM_SRC_ANONYMOUS_THP) {
>> -- 
>> 2.21.0
>>
>