[Bug 271333] kernel panic 13.2-RELEASE

From: <bugzilla-noreply_at_freebsd.org>
Date: Tue, 09 May 2023 19:05:02 UTC

Mark Johnston <markj@FreeBSD.org> changed:

           What    |Removed                     |Added
                 CC|                            |markj@FreeBSD.org
             Status|New                         |Open

--- Comment #1 from Mark Johnston <markj@FreeBSD.org> ---
Looks like a LinuxKPI bug:
- i915_vma_coredump contains an array of pages, freed in
__i915_gpu_coredump_free() -> cleanup_gt() -> i915_vma_coredump_free() with

    for (page = 0; page < vma->page_count; page++)
        free_page((unsigned long)vma->pages[page]);

- free_page() just calls FreeBSD's kmem_free().  That is, it expects to receive
a page mapped into the kernel map.

- Looks like those pages are allocated by pool_alloc() in i915_gpu_error.c.  It
uses alloc_page() in the LinuxKPI, which just allocates and returns an unmapped
page.  pool_alloc() extracts the direct map address.

So, i915kms is passing a direct map address to free_page(), which doesn't
handle that.  Probably free_page() should handle direct-mapped addresses by
resolving them to a page and freeing that with linux_free_pages(page, 0).

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