Re: [kvm-unit-tests PATCH v2 2/4] lib: s390x: sie: Allocate physical guest memory via memalign

Christoph Schlameuss
2026-04-21T15:31:17Z

On Tue Apr 21, 2026 at 5:16 PM CEST, Christoph Schlameuss wrote:
> On Mon Apr 20, 2026 at 10:44 AM CEST, Janosch Frank wrote:
>> alloc_pages_flags() alignes the allocation on the same order as its
>> requested size. Since we use virtual memory for SIE we can instead
>> align to 1MB by using memalign() which is less wasteful.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>> lib/s390x/sie.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/s390x/sie.c b/lib/s390x/sie.c
>> index 47d4cdde..b1b0a8a0 100644
>> --- a/lib/s390x/sie.c
>> +++ b/lib/s390x/sie.c
>> @@ -171,7 +171,8 @@ uint8_t *sie_guest_alloc(uint64_t guest_size)
>> guest_virt = (uint8_t *)ALIGN(get_ram_size() + guest_counter * 4UL * SZ_1G, SZ_2G);
>> guest_counter++;
>>
>> - guest_phys = alloc_pages(get_order(guest_size) - 12);
>> + guest_phys = memalign_pages_flags(SZ_1M, guest_size, 0);
>
> There is a const for that:
>
> guest_phys = memalign_pages_flags(SZ_1M, guest_size, AREA_ANY);
>

Oh, and with that fixed:

Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>

>> + assert(guest_phys);
>> /*
>> * Establish a new mapping of the guest memory so it can be 2GB aligned
>> * without actually requiring 2GB physical memory.