Re: Reg. Tee init fail...

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Adding Juergen and Boris because this is a Linux/x86 issue.


As you can see from this Linux driver:
https://elixir.bootlin.com/linux/latest/source/drivers/crypto/ccp/tee-dev.c#L132

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?



On Fri, 24 Jun 2022, Julien Grall wrote:
> Hi,
> 
> (moving the discussion to xen-devel as I think it is more appropriate)
> 
> On 24/06/2022 10:53, SK, SivaSangeetha (Siva Sangeetha) wrote:
> > [AMD Official Use Only - General]
> 
> Not clear what this means.
> 
> > 
> > Hi Xen team,
> > 
> > In TEE driver, We allocate a ring buffer, get its physical address from
> > __pa() macro, pass the physical address to secure processor for mapping it
> > and using in secure processor side.
> > 
> > Source:
> > https://elixir.bootlin.com/linux/latest/source/drivers/crypto/ccp/tee-dev.c#L132
> > 
> > This works good natively in Dom0 on the target.
> > When we boot the same Dom0 kernel, with Xen hypervisor enabled, ring init
> > fails.
> 
> Do you have any error message or error code?
> 
> > 
> > 
> > We suspect that the address passed to secure processor, is not same when xen
> > is enabled, and when xen is enabled, some level of address translation might
> > be required to get exact physical address.
> 
> If you are using Xen upstream, Dom0 will be mapped with IPA == PA. So there
> should be no need for translation.
> 
> Can you provide more details on your setup (version of Xen, Linux...)?
> 
> Cheers,
> 
> -- 
> Julien Grall
>