linux-kernel - Re: [PATCH v4 09/14] selftests: harness: Move teardown conditional into test metadata

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Message-ID: <20250612135802.GU543171@nvidia.com>
Date: Thu, 12 Jun 2025 10:58:02 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
	Shuah Khan <shuah@...nel.org>,
	Shuah Khan <skhan@...uxfoundation.org>, Willy Tarreau <w@....eu>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...capital.net>,
	Will Drewry <wad@...omium.org>, Mark Brown <broonie@...nel.org>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v4 09/14] selftests: harness: Move teardown conditional
 into test metadata

On Wed, Jun 11, 2025 at 11:59:00PM -0700, Nicolin Chen wrote:

> We can see the 64MB was rounded up to 512MB by ksys_mmap_pgoff()
> when being passed in to hugetlb_file_setup() at:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/mmap.c?h=v6.16-rc1#n594
> "		len = ALIGN(len, huge_page_size(hs));  "
> 
> By looking at the comments here..:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/hugetlbfs/inode.c#n1521
> "
> /*
>  * Note that size should be aligned to proper hugepage size in caller side,
>  * otherwise hugetlb_reserve_pages reserves one less hugepages than intended.
>  */
> struct file *hugetlb_file_setup(const char *name, size_t size,
> "
> 
> ..I guess this function was supposed to fail the not-a-multiple
> case as you remarked? But it certainly can't do that, when that
> size passed in is already hugepage-aligned..
> 
> It feels like a kernel bug as you suspect :-/

Certainly is
 
> And I just found one more weird thing...
> 
> In iommufd.c selftest code, we have:
> "static __attribute__((constructor)) void setup_sizes(void)"
> where it does another pair of posix_memalign/mmap, although this
> one doesn't flag MAP_HUGETLB and shouldn't impact what is coming
> to the next...

This could all just be more weirdness from the above, it doesn't
really make alot of sense.

I think change things so the MAP_HUGETLB test all skip if
HUGEPAGE_SIZE < buffer_size and move on..

Can't run those tests on ARM64 64k which is unfortunate.. I thought
there were patches to give that config a 2M huge page size option
based on the new contiguous page support though? Maybe it was only THPS..

Jason