linux-kernel - Re: [PATCH] dma-direct: use the correct size for dma_set

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Date:   Thu, 23 Jun 2022 10:01:34 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Dexuan Cui <decui@...rosoft.com>, Christoph Hellwig <hch@....de>
Cc:     "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Andrea Parri <Andrea.Parri@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>
Subject: Re: [PATCH] dma-direct: use the correct size for dma_set_encrypted()

On 2022-06-23 08:00, Dexuan Cui wrote:
>> From: Christoph Hellwig <hch@....de>
>> Sent: Wednesday, June 22, 2022 10:44 PM
>> To: Dexuan Cui <decui@...rosoft.com>
>>   ...
>> On Wed, Jun 22, 2022 at 12:14:24PM -0700, Dexuan Cui wrote:
>>> The third parameter of dma_set_encrypted() is a size in bytes rather than
>>> the number of pages.
>>>
>>> Fixes: 4d0564785bb0 ("dma-direct: factor out dma_set_{de,en}crypted
>> helpers")
>>> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
>>
>> see:
>>
>> commit 4a37f3dd9a83186cb88d44808ab35b78375082c9 (tag:
>> dma-mapping-5.19-2022-05-25)
>> Author: Robin Murphy <robin.murphy@....com>
>> Date:   Fri May 20 18:10:13 2022 +0100
>>
>>      dma-direct: don't over-decrypt memory
> 
> It looks like commit 4a37f3dd9a831 fixed a different issue?
> 
> Here my patch is for the latest mainline:
> 
> In dma_direct_alloc()'s error handling path, we pass 'size' to dma_set_encrypted():
>    out_encrypt_pages:
> 	  if (dma_set_encrypted(dev, page_address(page), size))
> 
> However, in dma_direct_free(), we pass ' 1 << page_order ' to dma_set_encrypted().
> I think the ' 1 << page_order' is incorrect and it should be 'size' as well?

I think technically you're both right - these instances clearly have a 
history tracing back to the original bug that my patch addressed, but 
the refactoring then made them into their own distinct bug in terms of 
the internal dma_set_encrypted() interface, per the commit message here. 
Apparently I failed to spot this when forward-porting 4a37f3dd9a831 from 
5.10 (as the commit message says, don't ask... ;) ) - I guess I was only 
looking at where the set_memory_*() callsites had moved to. For this patch,

Reviewed-by: Robin Murphy <robin.murphy@....com>

Thanks
Robin.