Re: [PATCH 2/2] iommufd/selftest: Test reserved regions near ULONG_MAX

[Robin Murphy <robin.murphy@arm.com>]

On 2025-07-18 9:13 am, Nicolin Chen wrote:
> On Thu, Jul 17, 2025 at 07:45:51PM -0700, Nicolin Chen wrote:
>> On Thu, Jul 17, 2025 at 04:15:09PM -0300, Jason Gunthorpe wrote:
>>
>>> +TEST_F(iommufd_ioas, reserved_overflow)
>>> +{
>>> +	struct iommu_test_cmd test_cmd = {
>>> +		.size = sizeof(test_cmd),
>>> +		.op = IOMMU_TEST_OP_ADD_RESERVED,
>>> +		.id = self->ioas_id,
>>> +		.add_reserved = { .start = 6,
>>> +				  .length = 0xffffffffffff8001 },
>>> +	};
>>> +	__u64 iova;
>>> +
>>> +	ASSERT_EQ(0,
>>> +		  ioctl(self->fd, _IOMMU_TEST_CMD(IOMMU_TEST_OP_ADD_RESERVED),
>>> +			&test_cmd));
>>> +	test_err_ioctl_ioas_map(ENOSPC, buffer, 0x5000, &iova);
>>
>> When:
>> PAGE_SIZE=SZ_64K = 0x10000
>> MOCK_PAGE_SIZE = PAGE_SIZE / 2 = 0x8000
>>
>> This likely fails the alignment test, returning -EINVAL instead:
>>
>> # iommufd.c:988:reserved_overflow:Expected 28 (28) == errno (22)
>> # reserved_overflow: Test failed
>> #          FAIL  iommufd_ioas.mock_domain_limit.reserved_overflow
>>
>> So, I think we'd have to pick a number aligned to MOCK_PAGE_SIZE?
>> e.g. changing to 0x18000 for example can pass.
> 
> I realized that we can't change the number as it won't reproduce
> on PAGE_SIZE=4K. So, perhaps it should just SKIP other page sizes
> than 4K.

Shouldn't it work to parametrise both numbers accordingly, e.g. (if my 
Friday-evening maths holds up) reserve "1UL - MOCK_PAGE_SIZE * 16" then 
map "MOCK_PAGE_SIZE * 10"?

Robin.