Re: [PATCH 1/6] mm/selftests: Fix virtual_address_range test issues.

[Dev Jain <dev.jain@arm.com>]

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On 23/06/25 11:02 pm, Donet Tom wrote:
> On Mon, Jun 23, 2025 at 10:23:02AM +0530, Dev Jain wrote:
>> On 21/06/25 11:25 pm, Donet Tom wrote:
>>> On Fri, Jun 20, 2025 at 08:15:25PM +0530, Dev Jain wrote:
>>>> On 19/06/25 1:53 pm, Donet Tom wrote:
>>>>> On Wed, Jun 18, 2025 at 08:13:54PM +0530, Dev Jain wrote:
>>>>>> On 18/06/25 8:05 pm, Lorenzo Stoakes wrote:
>>>>>>> On Wed, Jun 18, 2025 at 07:47:18PM +0530, Dev Jain wrote:
>>>>>>>> On 18/06/25 7:37 pm, Lorenzo Stoakes wrote:
>>>>>>>>> On Wed, Jun 18, 2025 at 07:28:16PM +0530, Dev Jain wrote:
>>>>>>>>>> On 18/06/25 5:27 pm, Lorenzo Stoakes wrote:
>>>>>>>>>>> On Wed, Jun 18, 2025 at 05:15:50PM +0530, Dev Jain wrote:
>>>>>>>>>>> Are you accounting for sys.max_map_count? If not, then you'll be hitting that
>>>>>>>>>>> first.
>>>>>>>>>> run_vmtests.sh will run the test in overcommit mode so that won't be an issue.
>>>>>>>>> Umm, what? You mean overcommit all mode, and that has no bearing on the max
>>>>>>>>> mapping count check.
>>>>>>>>>
>>>>>>>>> In do_mmap():
>>>>>>>>>
>>>>>>>>> 	/* Too many mappings? */
>>>>>>>>> 	if (mm->map_count > sysctl_max_map_count)
>>>>>>>>> 		return -ENOMEM;
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> As well as numerous other checks in mm/vma.c.
>>>>>>>> Ah sorry, didn't look at the code properly just assumed that overcommit_always meant overriding
>>>>>>>> this.
>>>>>>> No problem! It's hard to be aware of everything in mm :)
>>>>>>>
>>>>>>>>> I'm not sure why an overcommit toggle is even necessary when you could use
>>>>>>>>> MAP_NORESERVE or simply map PROT_NONE to avoid the OVERCOMMIT_GUESS limits?
>>>>>>>>>
>>>>>>>>> I'm pretty confused as to what this test is really achieving honestly. This
>>>>>>>>> isn't a useful way of asserting mmap() behaviour as far as I can tell.
>>>>>>>> Well, seems like a useful way to me at least : ) Not sure if you are in the mood
>>>>>>>> to discuss that but if you'd like me to explain from start to end what the test
>>>>>>>> is doing, I can do that : )
>>>>>>>>
>>>>>>> I just don't have time right now, I guess I'll have to come back to it
>>>>>>> later... it's not the end of the world for it to be iffy in my view as long as
>>>>>>> it passes, but it might just not be of great value.
>>>>>>>
>>>>>>> Philosophically I'd rather we didn't assert internal implementation details like
>>>>>>> where we place mappings in userland memory. At no point do we promise to not
>>>>>>> leave larger gaps if we feel like it :)
>>>>>> You have a fair point. Anyhow a debate for another day.
>>>>>>
>>>>>>> I'm guessing, reading more, the _real_ test here is some mathematical assertion
>>>>>>> about layout from HIGH_ADDR_SHIFT -> end of address space when using hints.
>>>>>>>
>>>>>>> But again I'm not sure that achieves much and again also is asserting internal
>>>>>>> implementation details.
>>>>>>>
>>>>>>> Correct behaviour of this kind of thing probably better belongs to tests in the
>>>>>>> userland VMA testing I'd say.
>>>>>>>
>>>>>>> Sorry I don't mean to do down work you've done before, just giving an honest
>>>>>>> technical appraisal!
>>>>>> Nah, it will be rather hilarious to see it all go down the drain xD
>>>>>>
>>>>>>> Anyway don't let this block work to fix the test if it's failing. We can revisit
>>>>>>> this later.
>>>>>> Sure. @Aboorva and Donet, I still believe that the correct approach is to elide
>>>>>> the gap check at the crossing boundary. What do you think?
>>>>>>
>>>>> One problem I am seeing with this approach is that, since the hint address
>>>>> is generated randomly, the VMAs are also being created at randomly based on
>>>>> the hint address.So, for the VMAs created at high addresses, we cannot guarantee
>>>>> that the gaps between them will be aligned to MAP_CHUNK_SIZE.
>>>>>
>>>>> High address VMAs
>>>>> -----------------
>>>>> 1000000000000-1000040000000 r--p 00000000 00:00 0
>>>>> 2000000000000-2000040000000 r--p 00000000 00:00 0
>>>>> 4000000000000-4000040000000 r--p 00000000 00:00 0
>>>>> 8000000000000-8000040000000 r--p 00000000 00:00 0
>>>>> e80009d260000-fffff9d260000 r--p 00000000 00:00 0
>>>>>
>>>>> I have a different approach to solve this issue.
>>>> It is really weird that such a large amount of VA space
>>>> is left between the two VMAs yet mmap is failing.
>>>>
>>>>
>>>>
>>>> Can you please do the following:
>>>> set /proc/sys/vm/max_map_count to the highest value possible.
>>>> If running without run_vmtests.sh, set /proc/sys/vm/overcommit_memory to 1.
>>>> In validate_complete_va_space:
>>>>
>>>> if (start_addr >= HIGH_ADDR_MARK && found == false) {
>>>> 	found = true;
>>>> 	continue;
>>>> }
>>> Thanks Dev for the suggestion. I set max_map_count and set overcommit
>>> memory to 1, added this code change as well, and then tried. Still, the
>>> test is failing
>>>
>>>> where found is initialized to false. This will skip the check
>>>> for the boundary.
>>>>
>>>> After this can you tell whether the test is still failing.
>>>>
>>>> Also can you give me the complete output of proc/pid/maps
>>>> after putting a sleep at the end of the test.
>>>>
>>> on powerpc support DEFAULT_MAP_WINDOW is 128TB and with
>>> total address space size is 4PB With hint it can map upto
>>> 4PB. Since the hint addres is random in this test random hing VMAs
>>> are getting created. IIUC this is expected only.
>>>
>>>
>>> 10000000-10010000 r-xp 00000000 fd:05 134226638                          /home/donet/linux/tools/testing/selftests/mm/virtual_address_range
>>> 10010000-10020000 r--p 00000000 fd:05 134226638                          /home/donet/linux/tools/testing/selftests/mm/virtual_address_range
>>> 10020000-10030000 rw-p 00010000 fd:05 134226638                          /home/donet/linux/tools/testing/selftests/mm/virtual_address_range
>>> 30000000-10030000000 r--p 00000000 00:00 0                               [anon:virtual_address_range]
>>> 10030770000-100307a0000 rw-p 00000000 00:00 0                            [heap]
>>> 1004f000000-7fff8f000000 r--p 00000000 00:00 0                           [anon:virtual_address_range]
>>> 7fff8faf0000-7fff8fe00000 rw-p 00000000 00:00 0
>>> 7fff8fe00000-7fff90030000 r-xp 00000000 fd:00 792355                     /usr/lib64/libc.so.6
>>> 7fff90030000-7fff90040000 r--p 00230000 fd:00 792355                     /usr/lib64/libc.so.6
>>> 7fff90040000-7fff90050000 rw-p 00240000 fd:00 792355                     /usr/lib64/libc.so.6
>>> 7fff90050000-7fff90130000 r-xp 00000000 fd:00 792358                     /usr/lib64/libm.so.6
>>> 7fff90130000-7fff90140000 r--p 000d0000 fd:00 792358                     /usr/lib64/libm.so.6
>>> 7fff90140000-7fff90150000 rw-p 000e0000 fd:00 792358                     /usr/lib64/libm.so.6
>>> 7fff90160000-7fff901a0000 r--p 00000000 00:00 0                          [vvar]
>>> 7fff901a0000-7fff901b0000 r-xp 00000000 00:00 0                          [vdso]
>>> 7fff901b0000-7fff90200000 r-xp 00000000 fd:00 792351                     /usr/lib64/ld64.so.2
>>> 7fff90200000-7fff90210000 r--p 00040000 fd:00 792351                     /usr/lib64/ld64.so.2
>>> 7fff90210000-7fff90220000 rw-p 00050000 fd:00 792351                     /usr/lib64/ld64.so.2
>>> 7fffc9770000-7fffc9880000 rw-p 00000000 00:00 0                          [stack]
>>> 1000000000000-1000040000000 r--p 00000000 00:00 0                        [anon:virtual_address_range]
>>> 2000000000000-2000040000000 r--p 00000000 00:00 0                        [anon:virtual_address_range]
>>> 4000000000000-4000040000000 r--p 00000000 00:00 0                        [anon:virtual_address_range]
>>> 8000000000000-8000040000000 r--p 00000000 00:00 0                        [anon:virtual_address_range]
>>> eb95410220000-fffff90220000 r--p 00000000 00:00 0                        [anon:virtual_address_range]
>>>
>>>
>>>
>>>
>>> If I give the hint address serially from 128TB then the address
>>> space is contigous and gap is also MAP_SIZE, the test is passing.
>>>
>>> 10000000-10010000 r-xp 00000000 fd:05 134226638                          /home/donet/linux/tools/testing/selftests/mm/virtual_address_range
>>> 10010000-10020000 r--p 00000000 fd:05 134226638                          /home/donet/linux/tools/testing/selftests/mm/virtual_address_range
>>> 10020000-10030000 rw-p 00010000 fd:05 134226638                          /home/donet/linux/tools/testing/selftests/mm/virtual_address_range
>>> 33000000-10033000000 r--p 00000000 00:00 0                               [anon:virtual_address_range]
>>> 10033380000-100333b0000 rw-p 00000000 00:00 0                            [heap]
>>> 1006f0f0000-10071000000 rw-p 00000000 00:00 0
>>> 10071000000-7fffb1000000 r--p 00000000 00:00 0                           [anon:virtual_address_range]
>>> 7fffb15d0000-7fffb1800000 r-xp 00000000 fd:00 792355                     /usr/lib64/libc.so.6
>>> 7fffb1800000-7fffb1810000 r--p 00230000 fd:00 792355                     /usr/lib64/libc.so.6
>>> 7fffb1810000-7fffb1820000 rw-p 00240000 fd:00 792355                     /usr/lib64/libc.so.6
>>> 7fffb1820000-7fffb1900000 r-xp 00000000 fd:00 792358                     /usr/lib64/libm.so.6
>>> 7fffb1900000-7fffb1910000 r--p 000d0000 fd:00 792358                     /usr/lib64/libm.so.6
>>> 7fffb1910000-7fffb1920000 rw-p 000e0000 fd:00 792358                     /usr/lib64/libm.so.6
>>> 7fffb1930000-7fffb1970000 r--p 00000000 00:00 0                          [vvar]
>>> 7fffb1970000-7fffb1980000 r-xp 00000000 00:00 0                          [vdso]
>>> 7fffb1980000-7fffb19d0000 r-xp 00000000 fd:00 792351                     /usr/lib64/ld64.so.2
>>> 7fffb19d0000-7fffb19e0000 r--p 00040000 fd:00 792351                     /usr/lib64/ld64.so.2
>>> 7fffb19e0000-7fffb19f0000 rw-p 00050000 fd:00 792351                     /usr/lib64/ld64.so.2
>>> 7fffc5470000-7fffc5580000 rw-p 00000000 00:00 0                          [stack]
>>> 800000000000-2aab000000000 r--p 00000000 00:00 0                         [anon:virtual_address_range]
>>>
>>>
>> Thank you for this output. I can't wrap my head around why this behaviour changes
>> when you generate the hint sequentially. The mmap() syscall is supposed to do the
>> following (irrespective of high VA space or not) - if the allocation at the hint
> Yes, it is working as expected. On PowerPC, the DEFAULT_MAP_WINDOW is
> 128TB, and the system can map up to 4PB.
>
> In the test, the first mmap call maps memory up to 128TB without any
> hint, so the VMAs are created below the 128TB boundary.
>
> In the second mmap call, we provide a hint starting from 256TB, and
> the hint address is generated randomly above 256TB. The mappings are
> correctly created at these hint addresses. Since the hint addresses
> are random, the resulting VMAs are also created at random locations.
>
> So, what I tried is: mapping from 0 to 128TB without any hint, and
> then for the second mmap, instead of starting the hint from 256TB, I
> started from 128TB. Instead of using random hint addresses, I used
> sequential hint addresses from 128TB up to 512TB. With this change,
> the VMAs are created in order, and the test passes.
>
> 800000000000-2aab000000000 r--p 00000000 00:00 0    128TB to 512TB VMA
>
> I think we will see same behaviour on x86 with X86_FEATURE_LA57.
>
> I will send the updated patch in V2.

Since you say it fails on both radix and hash, it means that the generic
code path is failing. I see that on my system, when I run the test with
LPA2 config, write() fails with errno set to -ENOMEM. Can you apply
the following diff and check whether the test fails still. Doing this
fixed it for arm64.

diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c

index b380e102b22f..3032902d01f2 100644

--- a/tools/testing/selftests/mm/virtual_address_range.c

+++ b/tools/testing/selftests/mm/virtual_address_range.c

@@ -173,10 +173,6 @@ static int validate_complete_va_space(void)

                  */

                 hop = 0;

                 while (start_addr + hop < end_addr) {

-                       if (write(fd, (void *)(start_addr + hop), 1) != 1)

-                               return 1;

-                       lseek(fd, 0, SEEK_SET);

-

                         if (is_marked_vma(vma_name))

                                 munmap((char *)(start_addr + hop), MAP_CHUNK_SIZE);

>
>> addr succeeds, then all is well, otherwise, do a top-down search for a large
>> enough gap. I am not aware of the nuances in powerpc but I really am suspecting
>> a bug in powerpc mmap code. Can you try to do some tracing - which function
>> eventually fails to find the empty gap?
>>
>> Through my limited code tracing - we should end up in slice_find_area_topdown,
>> then we ask the generic code to find the gap using vm_unmapped_area. So I
>> suspect something is happening between this, probably slice_scan_available().
>>
>>>>>    From 0 to 128TB, we map memory directly without using any hint. For the range above
>>>>> 256TB up to 512TB, we perform the mapping using hint addresses. In the current test,
>>>>> we use random hint addresses, but I have modified it to generate hint addresses linearly
>>>>> starting from 128TB.
>>>>>
>>>>> With this change:
>>>>>
>>>>> The 0–128TB range is mapped without hints and verified accordingly.
>>>>>
>>>>> The 128TB–512TB range is mapped using linear hint addresses and then verified.
>>>>>
>>>>> Below are the VMAs obtained with this approach:
>>>>>
>>>>> 10000000-10010000 r-xp 00000000 fd:05 135019531
>>>>> 10010000-10020000 r--p 00000000 fd:05 135019531
>>>>> 10020000-10030000 rw-p 00010000 fd:05 135019531
>>>>> 20000000-10020000000 r--p 00000000 00:00 0
>>>>> 10020800000-10020830000 rw-p 00000000 00:00 0
>>>>> 1004bcf0000-1004c000000 rw-p 00000000 00:00 0
>>>>> 1004c000000-7fff8c000000 r--p 00000000 00:00 0
>>>>> 7fff8c130000-7fff8c360000 r-xp 00000000 fd:00 792355
>>>>> 7fff8c360000-7fff8c370000 r--p 00230000 fd:00 792355
>>>>> 7fff8c370000-7fff8c380000 rw-p 00240000 fd:00 792355
>>>>> 7fff8c380000-7fff8c460000 r-xp 00000000 fd:00 792358
>>>>> 7fff8c460000-7fff8c470000 r--p 000d0000 fd:00 792358
>>>>> 7fff8c470000-7fff8c480000 rw-p 000e0000 fd:00 792358
>>>>> 7fff8c490000-7fff8c4d0000 r--p 00000000 00:00 0
>>>>> 7fff8c4d0000-7fff8c4e0000 r-xp 00000000 00:00 0
>>>>> 7fff8c4e0000-7fff8c530000 r-xp 00000000 fd:00 792351
>>>>> 7fff8c530000-7fff8c540000 r--p 00040000 fd:00 792351
>>>>> 7fff8c540000-7fff8c550000 rw-p 00050000 fd:00 792351
>>>>> 7fff8d000000-7fffcd000000 r--p 00000000 00:00 0
>>>>> 7fffe9c80000-7fffe9d90000 rw-p 00000000 00:00 0
>>>>> 800000000000-2000000000000 r--p 00000000 00:00 0    -> High Address (128TB to 512TB)
>>>>>
>>>>> diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
>>>>> index 4c4c35eac15e..0be008cba4b0 100644
>>>>> --- a/tools/testing/selftests/mm/virtual_address_range.c
>>>>> +++ b/tools/testing/selftests/mm/virtual_address_range.c
>>>>> @@ -56,21 +56,21 @@
>>>>>     #ifdef __aarch64__
>>>>>     #define HIGH_ADDR_MARK  ADDR_MARK_256TB
>>>>> -#define HIGH_ADDR_SHIFT 49
>>>>> +#define HIGH_ADDR_SHIFT 48
>>>>>     #define NR_CHUNKS_LOW   NR_CHUNKS_256TB
>>>>>     #define NR_CHUNKS_HIGH  NR_CHUNKS_3840TB
>>>>>     #else
>>>>>     #define HIGH_ADDR_MARK  ADDR_MARK_128TB
>>>>> -#define HIGH_ADDR_SHIFT 48
>>>>> +#define HIGH_ADDR_SHIFT 47
>>>>>     #define NR_CHUNKS_LOW   NR_CHUNKS_128TB
>>>>>     #define NR_CHUNKS_HIGH  NR_CHUNKS_384TB
>>>>>     #endif
>>>>> -static char *hint_addr(void)
>>>>> +static char *hint_addr(int hint)
>>>>>     {
>>>>> -       int bits = HIGH_ADDR_SHIFT + rand() % (63 - HIGH_ADDR_SHIFT);
>>>>> +       unsigned long addr = ((1UL << HIGH_ADDR_SHIFT) + (hint * MAP_CHUNK_SIZE));
>>>>> -       return (char *) (1UL << bits);
>>>>> +       return (char *) (addr);
>>>>>     }
>>>>>     static void validate_addr(char *ptr, int high_addr)
>>>>> @@ -217,7 +217,7 @@ int main(int argc, char *argv[])
>>>>>            }
>>>>>            for (i = 0; i < NR_CHUNKS_HIGH; i++) {
>>>>> -               hint = hint_addr();
>>>>> +               hint = hint_addr(i);
>>>>>                    hptr[i] = mmap(hint, MAP_CHUNK_SIZE, PROT_READ,
>>>>>                                   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>>>>>
>>>>>
>>>>>
>>>>> Can we fix it this way?

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