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Date:   Wed, 30 Jun 2021 12:43:48 +0100
From:   Will Deacon <will@kernel.org>
To:     Claire Chang <tientzu@chromium.org>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
        Joerg Roedel <joro@8bytes.org>,
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        "list@263.net:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
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        Qian Cai <quic_qiancai@quicinc.com>
Subject: Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for
 swiotlb data bouncing
Message-ID: <20210630114348.GA8383@willie-the-truck>
References: <20210624155526.2775863-1-tientzu@chromium.org>
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On Wed, Jun 30, 2021 at 05:17:27PM +0800, Claire Chang wrote:
> On Wed, Jun 30, 2021 at 9:43 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > On Thu, Jun 24, 2021 at 11:55:20PM +0800, Claire Chang wrote:
> > > Propagate the swiotlb_force into io_tlb_default_mem->force_bounce and
> > > use it to determine whether to bounce the data or not. This will be
> > > useful later to allow for different pools.
> > >
> > > Signed-off-by: Claire Chang <tientzu@chromium.org>
> > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > Tested-by: Stefano Stabellini <sstabellini@kernel.org>
> > > Tested-by: Will Deacon <will@kernel.org>
> > > Acked-by: Stefano Stabellini <sstabellini@kernel.org>
> >
> > This patch as commit af452ec1b1a3 ("swiotlb: Use is_swiotlb_force_bounce
> > for swiotlb data bouncing") causes my Ryzen 3 4300G system to fail to
> > get to an X session consistently (although not every single time),
> > presumably due to a crash in the AMDGPU driver that I see in dmesg.
> >
> > I have attached logs at af452ec1b1a3 and f127c9556a8e and I am happy
> > to provide any further information, debug, or test patches as necessary.
> 
> Are you using swiotlb=force? or the swiotlb_map is called because of
> !dma_capable? (https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/kernel/dma/direct.h#n93)

The command line is in the dmesg:

  | Kernel command line: initrd=\amd-ucode.img initrd=\initramfs-linux-next-llvm.img root=PARTUUID=8680aa0c-cf09-4a69-8cf3-970478040ee7 rw intel_pstate=no_hwp irqpoll

but I worry that this looks _very_ similar to the issue reported by Qian
Cai which we thought we had fixed. Nathan -- is the failure deterministic?

> `BUG: unable to handle page fault for address: 00000000003a8290` and
> the fact it crashed at `_raw_spin_lock_irqsave` look like the memory
> (maybe dev->dma_io_tlb_mem) was corrupted?
> The dev->dma_io_tlb_mem should be set here
> (https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/pci/probe.c#n2528)
> through device_initialize.

I'm less sure about this. 'dma_io_tlb_mem' should be pointing at
'io_tlb_default_mem', which is a page-aligned allocation from memblock.
The spinlock is at offset 0x24 in that structure, and looking at the
register dump from the crash:

Jun 29 18:28:42 hp-4300G kernel: RSP: 0018:ffffadb4013db9e8 EFLAGS: 00010006
Jun 29 18:28:42 hp-4300G kernel: RAX: 00000000003a8290 RBX: 0000000000000000 RCX: ffff8900572ad580
Jun 29 18:28:42 hp-4300G kernel: RDX: ffff89005653f024 RSI: 00000000000c0000 RDI: 0000000000001d17
Jun 29 18:28:42 hp-4300G kernel: RBP: 000000000a20d000 R08: 00000000000c0000 R09: 0000000000000000
Jun 29 18:28:42 hp-4300G kernel: R10: 000000000a20d000 R11: ffff89005653f000 R12: 0000000000000212
Jun 29 18:28:42 hp-4300G kernel: R13: 0000000000001000 R14: 0000000000000002 R15: 0000000000200000
Jun 29 18:28:42 hp-4300G kernel: FS:  00007f1f8898ea40(0000) GS:ffff890057280000(0000) knlGS:0000000000000000
Jun 29 18:28:42 hp-4300G kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Jun 29 18:28:42 hp-4300G kernel: CR2: 00000000003a8290 CR3: 00000001020d0000 CR4: 0000000000350ee0
Jun 29 18:28:42 hp-4300G kernel: Call Trace:
Jun 29 18:28:42 hp-4300G kernel:  _raw_spin_lock_irqsave+0x39/0x50
Jun 29 18:28:42 hp-4300G kernel:  swiotlb_tbl_map_single+0x12b/0x4c0

Then that correlates with R11 holding the 'dma_io_tlb_mem' pointer and
RDX pointing at the spinlock. Yet RAX is holding junk :/

I agree that enabling KASAN would be a good idea, but I also think we
probably need to get some more information out of swiotlb_tbl_map_single()
to see see what exactly is going wrong in there.

Will