Re: Reg. Tee init fail...

[Juergen Gross <jgross@suse.com>]

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On 11.08.22 00:55, Marek Marczykowski-Górecki wrote:
> On Thu, Jun 30, 2022 at 07:31:38AM +0200, Juergen Gross wrote:
>> On 30.06.22 05:32, SK, SivaSangeetha (Siva Sangeetha) wrote:
>>> [AMD Official Use Only - General]
>>>
>>> +team
>>>
>>> -----Original Message-----
>>> From: Stefano Stabellini <sstabellini@kernel.org>
>>> Sent: Thursday, June 30, 2022 1:34 AM
>>> To: Julien Grall <julien@xen.org>
>>> Cc: SK, SivaSangeetha (Siva Sangeetha) <SivaSangeetha.SK@amd.com>; xen-devel@lists.xenproject.org; Stefano Stabellini <sstabellini@kernel.org>; Bertrand Marquis <bertrand.marquis@arm.com>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; jgross@suse.com; boris.ostrovsky@oracle.com
>>> Subject: Re: Reg. Tee init fail...
>>>
>>> Adding Juergen and Boris because this is a Linux/x86 issue.
>>>
>>>
>>> As you can see from this Linux driver:
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Flatest%2Fsource%2Fdrivers%2Fcrypto%2Fccp%2Ftee-dev.c%23L132&amp;data=05%7C01%7CSivaSangeetha.SK%40amd.com%7Ce962a907794f4917a80b08da5a0a7b3b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637921298315828104%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=NxmMUckiDRGLv3qLJrhZKBt2zNTuomEZqYJdV74tXxA%3D&amp;reserved=0
>>>
>>> Linux as dom0 on x86 is trying to communicate with firmware (TEE). Linux is calling __pa to pass a physical address to firmware. However, __pa returns a "fake" address not an mfn. I imagine that a quick workaround would be to call "virt_to_machine" instead of "__pa" in tee-dev.c.
>>>
>>> Normally, if this was a device, the "right fix" would be to use swiotlb-xen:xen_swiotlb_map_page to get back a real physical address.
>>>
>>> However, xen_swiotlb_map_page is meant to be used as part of the dma_ops API and takes a struct device *dev as input parameter. Maybe xen_swiotlb_map_page can be used for tee-dev as well?
>>>
>>>
>>> Basically tee-dev would need to call dma_map_page before passing addresses to firmware, and dma_unmap_page when it is done. E.g.:
>>>
>>>
>>>     cmd_buffer = dma_map_page(dev, virt_to_page(cmd),
>>>                               cmd & ~PAGE_MASK,
>>>                               ring_size,
>>>                               DMA_TO_DEVICE);
>>>
>>>
>>> Juergen, Boris,
>>> what do you think?
>>
>> Yes, I think using the DMA interface is the correct way to handle that.
>>
>> BTW, I did a similar fix for the dcdbas driver recently:
>>
>> https://lore.kernel.org/r/20220318150950.16843-1-jgross@suse.com
> 
> I hit similar issue, and the patch below made it work for me (ugly
> workaround), or at least stop complaining.
> 
> But note one of those places have this comment:
> 
> 	/* We need actual physical address instead of DMA address, since
> 	 * Trusted OS running on AMD Secure Processor will map this region
> 	 */
> 
> I guess it means AMD Secure Processor bypasses IOMMU...

It seems not to be attached via an IOMMU, same as for the DCDBAS fix,
where the address is used in SMM handler running on the main processor.

It should be possible to use DMA mapping in your case, too, as long as
the related device has the correct DMA settings not using any IOMMU
translations.


Juergen

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