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Subject: Re: Linux 5.1.9 build failure with
 CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT=n
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>
CC:     Sven Joachim <svenjoac@gmx.de>, stable <stable@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Airlie <airlied@redhat.com>
References: <87k1dsjkdo.fsf@turtle.gmx.de> <20190611153656.GA5084@kroah.com>
 <CAKMK7uH_3P3pYkJ9Ua4hOFno5UiQ4p-rdWu9tPO75MxGCbyXSA@mail.gmail.com>
 <20190611174006.GB31662@kroah.com>
From:   Thomas Backlund <tmb@mageia.org>
Message-ID: <11b2d815-d0c0-1f68-557d-144166c4a1a7@mageia.org>
Date:   Tue, 11 Jun 2019 22:08:10 +0300
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Den 11-06-2019 kl. 20:40, skrev Greg Kroah-Hartman:
> On Tue, Jun 11, 2019 at 07:33:16PM +0200, Daniel Vetter wrote:
>> On Tue, Jun 11, 2019 at 5:37 PM Greg Kroah-Hartman
>> <gregkh@linuxfoundation.org> wrote:
>>> On Tue, Jun 11, 2019 at 03:56:35PM +0200, Sven Joachim wrote:
>>>> Commit 1e07d63749 ("drm/nouveau: add kconfig option to turn off nouveau
>>>> legacy contexts. (v3)") has caused a build failure for me when I
>>>> actually tried that option (CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT=n):
>>>>
>>>> ,----
>>>> | Kernel: arch/x86/boot/bzImage is ready  (#1)
>>>> |   Building modules, stage 2.
>>>> |   MODPOST 290 modules
>>>> | ERROR: "drm_legacy_mmap" [drivers/gpu/drm/nouveau/nouveau.ko] undefined!
>>>> | scripts/Makefile.modpost:91: recipe for target '__modpost' failed
>>>> `----
>>
>> Calling drm_legacy_mmap is definitely not a great idea. I think either
>> we need a custom patch to remove that out on older kernels, or maybe
>> even #ifdef if you want to be super paranoid about breaking stuff ...
>>
>>>> Upstream does not have that problem, as commit bed2dd8421 ("drm/ttm:
>>>> Quick-test mmap offset in ttm_bo_mmap()") has removed the use of
>>>> drm_legacy_mmap from nouveau_ttm.c.  Unfortunately that commit does not
>>>> apply in 5.1.9.
>>>>
>>>> Most likely 4.19.50 and 4.14.125 are also affected, I haven't tested
>>>> them yet.
>>>
>>> They probably are.
>>>
>>> Should I just revert this patch in the stable tree, or add some other
>>> patch (like the one pointed out here, which seems an odd patch for
>>> stable...)
>>
>> ... or backport the above patch, that should be save to do too. Not
>> sure what stable folks prefer?
> 
> The above patch does not apply to all of the stable branches, so how
> about I just revert this?  People can live with this option not able to
> turn off for now, and if they really want it, they can use a newer
> kernel, right?
> 

Or add the simple fix suggested by Daniel (if I understand correctly):


From: Thomas Backlund <tmb@mageia.org>

Setting CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT=n (added by commit: 
b30a43ac7132) causes the build to fail with:

ERROR: "drm_legacy_mmap" [drivers/gpu/drm/nouveau/nouveau.ko] undefined!

Fix that by adding check for CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT around
the code using drm_legacy_mmap()

Fixes: b30a43ac7132 drm/nouveau: add kconfig option to turn off nouveau 
legacy contexts. (v3)
Signed-off-by: Thomas Backlund <tmb@mageia.org>

---
  drivers/gpu/drm/nouveau/nouveau_ttm.c |    2 ++
  1 file changed, 2 insertions(+)

--- a/drivers/gpu/drm/nouveau/nouveau_ttm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_ttm.c
@@ -168,8 +168,10 @@ nouveau_ttm_mmap(struct file *filp, stru
  	struct drm_file *file_priv = filp->private_data;
  	struct nouveau_drm *drm = nouveau_drm(file_priv->minor->dev);

+#if defined(CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT)
  	if (unlikely(vma->vm_pgoff < DRM_FILE_PAGE_OFFSET))
  		return drm_legacy_mmap(filp, vma);
+#endif

  	return ttm_bo_mmap(filp, vma, &drm->ttm.bdev);
  }