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Date:   Mon, 8 Jun 2020 19:31:47 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     "Alex Xu (Hello71)" <alex_y_xu@yahoo.ca>
cc:     Christoph Hellwig <hch@lst.de>, alsa-devel@alsa-project.org,
        bp@alien8.de, hch@infradead.org, hpa@zytor.com,
        linux-kernel@vger.kernel.org, mingo@redhat.com,
        Pavel Machek <pavel@ucw.cz>, perex@perex.cz,
        tglx@linutronix.de, tiwai@suse.com, x86@kernel.org
Subject: Re: next-0519 on thinkpad x60: sound related? window manager crash
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On Mon, 8 Jun 2020, Alex Xu (Hello71) wrote:

> Excerpts from Christoph Hellwig's message of June 8, 2020 2:19 am:
> > Can you do a listing using gdb where this happens?
> > 
> > gdb vmlinux
> > 
> > l *(snd_pcm_hw_params+0x3f3)
> > 
> > ?
> > 
> 
> (gdb) l *(snd_pcm_hw_params+0x3f3)
> 0xffffffff817efc85 is in snd_pcm_hw_params (.../linux/sound/core/pcm_native.c:749).
> 744             while (runtime->boundary * 2 <= LONG_MAX - runtime->buffer_size)
> 745                     runtime->boundary *= 2;
> 746
> 747             /* clear the buffer for avoiding possible kernel info leaks */
> 748             if (runtime->dma_area && !substream->ops->copy_user)
> 749                     memset(runtime->dma_area, 0, runtime->dma_bytes);
> 750
> 751             snd_pcm_timer_resolution_change(substream);
> 752             snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
> 753
> 

Working theory is that CONFIG_DMA_NONCOHERENT_MMAP getting set is causing 
the error_code in the page fault path.  Debugging with Alex off-thread we 
found that dma_{alloc,free}_from_pool() are not getting called from the 
new code in dma_direct_{alloc,free}_pages() and he has not enabled 
mem_encrypt.

So the issue is related to setting CONFIG_DMA_COHERENT_POOL, and not 
anything else related to AMD SME.  He has a patch to try out, but I wanted 
to update the thread in case there are other ideas to try other than 
selecting CONFIG_DMA_NONCOHERENT_MMAP only when CONFIG_DMA_REMAP is set 
(and not CONFIG_DMA_COHERENT_POOL).