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

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Message-ID: <20250612233138.GY543171@nvidia.com>
Date: Thu, 12 Jun 2025 20:31:38 -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 Thu, Jun 12, 2025 at 12:03:14PM -0700, Nicolin Chen wrote:
> On Thu, Jun 12, 2025 at 03:56:13PM -0300, Jason Gunthorpe wrote:
> > On Thu, Jun 12, 2025 at 11:53:24AM -0700, Nicolin Chen wrote:
> > > @@ -2022,7 +2023,19 @@ FIXTURE_SETUP(iommufd_dirty_tracking)
> > >         self->fd = open("/dev/iommu", O_RDWR);
> > >         ASSERT_NE(-1, self->fd);
> > > 
> > > -       rc = posix_memalign(&self->buffer, HUGEPAGE_SIZE, variant->buffer_size);
> > > +       if (variant->hugepages) {
> > > +               /*
> > > +                * Allocation must be aligned to the HUGEPAGE_SIZE, because the
> > > +                * following mmap() will automatically align the length to be a
> > > +                * multiple of the underlying huge page size. Failing to do the
> > > +                * same at this allocation will result in a memory overwrite by
> > > +                * the mmap().
> > > +                */
> > > +               size = __ALIGN_KERNEL(variant->buffer_size, HUGEPAGE_SIZE);
> > > +       } else {
> > > +               size = variant->buffer_size;
> > > +       }
> > > +       rc = posix_memalign(&self->buffer, HUGEPAGE_SIZE, size);
> > >         if (rc || !self->buffer) {
> > >                 SKIP(return, "Skipping buffer_size=%lu due to errno=%d",
> > >                            variant->buffer_size, rc);
> > > 
> > > It can just upsize the allocation, i.e. the test case will only
> > > use the first 64M or 128MB out of the reserved 512MB huge page.
> > 
> > The MAP_HUGETLBFS is required that is the whole point of what it is
> > doing..
> 
> I am not quite following this.. MAP_HUGETLB will be still set.
> 
> And the underlying selftest case is using:
> 	MOCK_HUGE_PAGE_SIZE = 512 * MOCK_IO_PAGE_SIZE
> 
> Does it matter if the underlying allocation has an overshot?

I expect munmap won't work with the wrong size and the test will OOM?

You'd be better to correct the actual variant->buffer_size..

Jason