linux-kernel - Re: [syzbot] [iommu?] kernel BUG in dma_alloc

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Message-ID: <da9db10e-98fd-405c-9167-a29235f5470b@linux.dev>
Date: Thu, 17 Oct 2024 10:31:40 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Christoph Hellwig <hch@....de>,
 syzbot <syzbot+b4bfacdec173efaa8567@...kaller.appspotmail.com>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
 m.szyprowski@...sung.com, robin.murphy@....com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [iommu?] kernel BUG in dma_alloc_attrs

On 10/16/24 04:02, Christoph Hellwig wrote:
> The problem is that the dma alloc/free tracing calls virt_to_phys
> on the allocated/free memory.  But that memory can be vmalloced as
> in this case.  I think we don't have weirdo allocators or pools any
> more that are neither in the direct kernel mapping or vmalloc, so
> we might be able to do an
> 
> 		if (is_vmalloc_addr())
> 			page_to_phys(vmalloc_to_page()))

Do we need offset_in_page?

> 		else
> 			virt_to_page()
> 
> here.  Or just switch to tracing the virtual address to always be
> on the safe side.
> 

Since this function returns a virtual address, I think that would be
fine.

--Sean