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

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jan 23, 2017 at 04:33:08PM +0000, Catalin Marinas wrote:
> On Mon, Jan 23, 2017 at 05:15:39PM +0100, Geert Uytterhoeven wrote:
> > On Mon, Jan 23, 2017 at 5:02 PM,  <gregkh@linuxfoundation.org> 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@vger.kernel.org> know about it.
> > >
> > >
> > > From 524dabe1c68e0bca25ce7b108099e5d89472a101 Mon Sep 17 00:00:00 2001
> > > From: Alexander Graf <agraf@suse.de>
> > > Date: Mon, 16 Jan 2017 12:46:33 +0100
> > > Subject: arm64: Fix swiotlb fallback allocation
> > >
> > > From: Alexander Graf <agraf@suse.de>
> > >
> > > 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@suse.de>
> > > CC: Jisheng Zhang <jszhang@marvell.com>
> > > CC: Geert Uytterhoeven <geert+renesas@glider.be>
> > > CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > >
> > > ---
> > >  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).

Those look fine, I've queued them up now (took a bit of manual work),
and will let the autobuilder have fun with it...

thanks,

greg k-h