Re: Patch "arm64: Fix swiotlb fallback allocation" has been added to the 4.9-stable tree

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On Mon, Jan 23, 2017 at 05:15:39PM +0100, Geert Uytterhoeven wrote:
> On Mon, Jan 23, 2017 at 5:02 PM,  <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > This is a note to let you know that I've just added the patch titled
> >
> >     arm64: Fix swiotlb fallback allocation
> >
> > to the 4.9-stable tree which can be found at:
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> >
> > The filename of the patch is:
> >      arm64-fix-swiotlb-fallback-allocation.patch
> > and it can be found in the queue-4.9 subdirectory.
> >
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@xxxxxxxxxxxxxxx> know about it.
> >
> >
> > From 524dabe1c68e0bca25ce7b108099e5d89472a101 Mon Sep 17 00:00:00 2001
> > From: Alexander Graf <agraf@xxxxxxx>
> > Date: Mon, 16 Jan 2017 12:46:33 +0100
> > Subject: arm64: Fix swiotlb fallback allocation
> >
> > From: Alexander Graf <agraf@xxxxxxx>
> >
> > commit 524dabe1c68e0bca25ce7b108099e5d89472a101 upstream.
> >
> > Commit b67a8b29df introduced logic to skip swiotlb allocation when all memory
> > is DMA accessible anyway.
> >
> > While this is a great idea, __dma_alloc still calls swiotlb code unconditionally
> > to allocate memory when there is no CMA memory available. The swiotlb code is
> > called to ensure that we at least try get_free_pages().
> >
> > Without initialization, swiotlb allocation code tries to access io_tlb_list
> > which is NULL. That results in a stack trace like this:
> >
> >   Unable to handle kernel NULL pointer dereference at virtual address 00000000
> >   [...]
> >   [<ffff00000845b908>] swiotlb_tbl_map_single+0xd0/0x2b0
> >   [<ffff00000845be94>] swiotlb_alloc_coherent+0x10c/0x198
> >   [<ffff000008099dc0>] __dma_alloc+0x68/0x1a8
> >   [<ffff000000a1b410>] drm_gem_cma_create+0x98/0x108 [drm]
> >   [<ffff000000abcaac>] drm_fbdev_cma_create_with_funcs+0xbc/0x368 [drm_kms_helper]
> >   [<ffff000000abcd84>] drm_fbdev_cma_create+0x2c/0x40 [drm_kms_helper]
> >   [<ffff000000abc040>] drm_fb_helper_initial_config+0x238/0x410 [drm_kms_helper]
> >   [<ffff000000abce88>] drm_fbdev_cma_init_with_funcs+0x98/0x160 [drm_kms_helper]
> >   [<ffff000000abcf90>] drm_fbdev_cma_init+0x40/0x58 [drm_kms_helper]
> >   [<ffff000000b47980>] vc4_kms_load+0x90/0xf0 [vc4]
> >   [<ffff000000b46a94>] vc4_drm_bind+0xec/0x168 [vc4]
> >   [...]
> >
> > Thankfully swiotlb code just learned how to not do allocations with the FORCE_NO
> > option. This patch configures the swiotlb code to use that if we decide not to
> > initialize the swiotlb framework.
> >
> > Fixes: b67a8b29df ("arm64: mm: only initialize swiotlb when necessary")
> > Signed-off-by: Alexander Graf <agraf@xxxxxxx>
> > CC: Jisheng Zhang <jszhang@xxxxxxxxxxx>
> > CC: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> > CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> >
> > ---
> >  arch/arm64/mm/init.c |    2 ++
> >  1 file changed, 2 insertions(+)
> >
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -403,6 +403,8 @@ void __init mem_init(void)
> >  {
> >         if (swiotlb_force || max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT))
> >                 swiotlb_init(1);
> > +       else
> > +               swiotlb_force = SWIOTLB_NO_FORCE;
> 
> The above definition depends on:
> 
> commit ae7871be189cb411 ("swiotlb: Convert swiotlb_force from int to enum")
> commit fff5d99225107f5f ("swiotlb: Add swiotlb=noforce debug option")

If these are not suitable for stable (too big, new feature), we can just
drop the arm64 commit from 4.9-stable (and we could fix it in a
different way).

-- 
Catalin
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