Re: [PATCH v5 3/3] selftests/lam: Add test cases for different LAM tag widths

[Maciej Wieczor-Retman]

On 2026-04-07 at 13:06:40 -0700, Sohil Mehta wrote:
>The subject needs a change. No new tests are being added now, right?

Oh, right, I'll correct that.

>On 4/7/2026 10:45 AM, Maciej Wieczor-Retman wrote:
>> From: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
>>
>> diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
>> index 1919fa6daec0..d27f947ea694 100644
>> --- a/tools/testing/selftests/x86/lam.c
>> +++ b/tools/testing/selftests/x86/lam.c
>> @@ -26,9 +26,9 @@
>>
>>  /* LAM modes, these definitions were copied from kernel code */
>>  #define LAM_NONE                0
>> -#define LAM_U57_BITS            6
>> +#define LAM_BITS                4
>>
>> -#define LAM_U57_MASK            (0x3fULL << 57)
>> +#define LAM_MASK                (0xfULL << 57)
>
>How about calculating the LAM_MASK from the LAM bits similar to the core
>code in patch 1?
>
>Also, when copying over the defines it would be useful to name them
>exactly the same as the core code. That way any name changes would
>happen in sync.

Yes, both of these sound handy, I'll change it.

>
>> @@ -247,10 +247,10 @@ static uint64_t set_metadata(uint64_t src, unsigned long lam)
>>  	srand(time(NULL));
>>
>>  	switch (lam) {
>> -	case LAM_U57_BITS: /* Set metadata in bits 62:57 */
>> +	case LAM_BITS: /* Set metadata in bits 62:57 */
>
>This needs to change to 60:57 similar to the change below.

Hah, thanks, I thought I got them all :)

>
>>  		/* Get a random non-zero value as metadata */
>> -		metadata = (rand() % ((1UL << LAM_U57_BITS) - 1) + 1) << 57;
>> -		metadata |= (src & ~(LAM_U57_MASK));
>> +		metadata = (rand() % ((1UL << LAM_BITS) - 1) + 1) << 57;
>> +		metadata |= (src & ~(LAM_MASK));
>>  		break;
>>  	default:
>>  		metadata = src;
>> @@ -291,7 +291,7 @@ int handle_max_bits(struct testcases *test)
>>  	unsigned long bits = 0;
>>
>>  	if (exp_bits != LAM_NONE)
>> -		exp_bits = LAM_U57_BITS;
>> +		exp_bits = LAM_BITS;
>>
>>  	/* Get LAM max tag bits */
>>  	if (syscall(SYS_arch_prctl, ARCH_GET_MAX_TAG_BITS, &bits) == -1)
>> @@ -719,8 +719,8 @@ int do_uring(unsigned long lam)
>>  			uint64_t addr = ((uint64_t)fi->iovecs[i].iov_base);
>>
>>  			switch (lam) {
>> -			case LAM_U57_BITS: /* Clear bits 62:57 */
>> -				addr = (addr & ~(LAM_U57_MASK));
>> +			case LAM_BITS: /* Clear bits 60:57 */
>
>Just like this one.

-- 
Kind regards
Maciej Wieczór-Retman