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Date:   Tue, 8 Aug 2023 15:47:26 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Karol Herbst <kherbst@redhat.com>
Cc:     Ben Skeggs <bskeggs@redhat.com>, regressions@leemhuis.info,
        Lyude Paul <lyude@redhat.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: 2b5d1c29f6c4 ("drm/nouveau/disp: PIOR DP uses GPIO for HPD, not
 PMGR AUX interrupts")
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On Tue, Aug 08, 2023 at 12:39:32PM +0200, Karol Herbst wrote:
> ahh, that would have been good to know :)

Yeah, I didn't see it before - it would only freeze. Only after I added
the printk you requested.

> Mind figuring out what's exactly NULL inside nvif_object_mthd? Or
> rather what line `nvif_object_mthd+0x136` belongs to, then it should
> be easy to figure out what's wrong here.

That looks like this:

ffffffff816ddfee:       e8 8d 04 4e 00          callq  ffffffff81bbe480 <__memcpy>
ffffffff816ddff3:       41 8d 56 20             lea    0x20(%r14),%edx
ffffffff816ddff7:       49 8b 44 24 08          mov    0x8(%r12),%rax
ffffffff816ddffc:       83 fa 17                cmp    $0x17,%edx
ffffffff816ddfff:       76 7d                   jbe    ffffffff816de07e <nvif_object_mthd+0x1ae>
ffffffff816de001:       49 39 c4                cmp    %rax,%r12
ffffffff816de004:       74 45                   je     ffffffff816de04b <nvif_object_mthd+0x17b>

<--- RIP points here.

The 0x20 also fits the deref address: 0000000000000020.

Which means %rax is 0. Yap.

ffffffff816de006:       48 8b 78 20             mov    0x20(%rax),%rdi
ffffffff816de00a:       4c 89 64 24 10          mov    %r12,0x10(%rsp)
ffffffff816de00f:       48 8b 40 38             mov    0x38(%rax),%rax
ffffffff816de013:       c6 44 24 06 ff          movb   $0xff,0x6(%rsp)
ffffffff816de018:       31 c9                   xor    %ecx,%ecx
ffffffff816de01a:       48 89 e6                mov    %rsp,%rsi
ffffffff816de01d:       48 8b 40 28             mov    0x28(%rax),%rax
ffffffff816de021:       e8 3a 0c 4f 00          callq  ffffffff81bcec60 <__x86_indirect_thunk_array>


Now, the preprocessed asm version of nvif/object.c says around here:


	call	memcpy	#
# drivers/gpu/drm/nouveau/nvif/object.c:160: 	ret = nvif_object_ioctl(object, args, sizeof(*args) + size, NULL);
	leal	32(%r14), %edx	#, _108
# drivers/gpu/drm/nouveau/nvif/object.c:33: 	struct nvif_client *client = object->client;
	movq	8(%r12), %rax	# object_19(D)->client, client
# drivers/gpu/drm/nouveau/nvif/object.c:38: 	if (size >= sizeof(*args) && args->v0.version == 0) {
	cmpl	$23, %edx	#, _108
	jbe	.L69	#,
# drivers/gpu/drm/nouveau/nvif/object.c:39: 		if (object != &client->object)
	cmpq	%rax, %r12	# client, object
	je	.L70	#,
# drivers/gpu/drm/nouveau/nvif/object.c:47: 	return client->driver->ioctl(client->object.priv, data, size, hack);
	movq	32(%rax), %rdi	# client_109->object.priv, client_109->object.priv


So I'd say that client is NULL. IINM.


	movq	%r12, 16(%rsp)	# object, MEM[(union  *)&stack].v0.object
# drivers/gpu/drm/nouveau/nvif/object.c:47: 	return client->driver->ioctl(client->object.priv, data, size, hack);
	movq	56(%rax), %rax	# client_109->driver, client_109->driver
# drivers/gpu/drm/nouveau/nvif/object.c:43: 		args->v0.owner = NVIF_IOCTL_V0_OWNER_ANY;
	movb	$-1, 6(%rsp)	#, MEM[(union  *)&stack].v0.owner
.L64:
# drivers/gpu/drm/nouveau/nvif/object.c:47: 	return client->driver->ioctl(client->object.priv, data, size, hack);
	xorl	%ecx, %ecx	#
	movq	%rsp, %rsi	#,
	movq	40(%rax), %rax	#, _77->ioctl
	call	__x86_indirect_thunk_rax
# drivers/gpu/drm/nouveau/nvif/object.c:161: 	memcpy(data, args->mthd.data, size);

> > [    4.144676] #PF: supervisor read access in kernel mode
> > [    4.144676] #PF: error_code(0x0000) - not-present page
> > [    4.144676] PGD 0 P4D 0
> > [    4.144676] Oops: 0000 [#1] PREEMPT SMP PTI
> > [    4.144676] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5-dirty #1
> > [    4.144676] Hardware name: Dell Inc. Precision T3600/0PTTT9, BIOS A13 05/11/2014
> > [    4.144676] RIP: 0010:nvif_object_mthd+0x136/0x1e0
> > [    4.144676] Code: f2 4c 89 ee 48 8d 7c 24 20 66 89 04 24 c6 44 24 18 00 e8 8d 04 4e 00 41 8d 56 20 49 8b 44 24 08 83 fa 17 76 7d 49 39 c4 74 45 <48> 8b 78 20 4c 89 64 24 10 48 8b 40 38 c6 44 24 06 ff 31 c9 48 89

Opcode bytes around RIP look correct too:

./scripts/decodecode < /tmp/oops
[ 4.144676] Code: f2 4c 89 ee 48 8d 7c 24 20 66 89 04 24 c6 44 24 18 00 e8 8d 04 4e 00 41 8d 56 20 49 8b 44 24 08 83 fa 17 76 7d 49 39 c4 74 45 <48> 8b 78 20 4c 89 64 24 10 48 8b 40 38 c6 44 24 06 ff 31 c9 48 89
All code
========
   0:   f2 4c 89 ee             repnz mov %r13,%rsi
   4:   48 8d 7c 24 20          lea    0x20(%rsp),%rdi
   9:   66 89 04 24             mov    %ax,(%rsp)
   d:   c6 44 24 18 00          movb   $0x0,0x18(%rsp)
  12:   e8 8d 04 4e 00          callq  0x4e04a4
  17:   41 8d 56 20             lea    0x20(%r14),%edx
  1b:   49 8b 44 24 08          mov    0x8(%r12),%rax
  20:   83 fa 17                cmp    $0x17,%edx
  23:   76 7d                   jbe    0xa2
  25:   49 39 c4                cmp    %rax,%r12
  28:   74 45                   je     0x6f
  2a:*  48 8b 78 20             mov    0x20(%rax),%rdi          <-- trapping instruction
  2e:   4c 89 64 24 10          mov    %r12,0x10(%rsp)
  33:   48 8b 40 38             mov    0x38(%rax),%rax
  37:   c6 44 24 06 ff          movb   $0xff,0x6(%rsp)
  3c:   31 c9                   xor    %ecx,%ecx
  3e:   48                      rex.W
  3f:   89                      .byte 0x89


HTH.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette