RE: [Xen-devel] SMMU permission fault on Dom0 when init vpu_decoder

[Peng Fan <peng.fan@xxxxxxx>]

> Subject: [Xen-devel] SMMU permission fault on Dom0 when init vpu_decoder
> 
> Hello,
> 
> I'm getting permission fault from SMMU when trying to init
> VPU_Encoder/Decoder in Dom0 on IMX8QM board:
> (XEN) smmu: /iommu@51400000: Unhandled context fault: fsr=0x408,
> iova=0x86000a60, fsynr=0x1c0062, cb=0 This error appears when
> vpu_encoder/decoder tries to memcpy firmware image to
> 0x86000000 address, which is defined in reserved-memory node in xen
> device-tree as encoder_boot/decoder_boot region.
> 
> I'm using xen from branch xen-project/staging-4.16 + imx related patches,
> which were taken from
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsource.c
> odeaurora.org%2Fexternal%2Fimx%2Fimx-xen&data=05%7C01%7Cpeng.f
> an%40nxp.com%7C91e3a953942d414dcc6208da425006e7%7C686ea1d3bc2b
> 4c6fa92cd99c5c301635%7C0%7C0%7C637895208732114203%7CUnknown%
> 7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiL
> CJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=no%2BV2ubjGmrsm96NP
> ybeeug4a3BXx3oX7xmylzZCU8E%3D&reserved=0.
> 
> After some investigation I found that this issue was fixed by Peng Fan in
> commit: 46b3dd3718144ca6ac2c12a3b106e57fb7156554 (Hash from
> codeaurora), but only for the Guest domains.
> It introduces new p2m_type p2m_mmio_direct_nc_x, which differs from
> p2m_mmio_direct_nc by XN = 0. This type is set to the reserved memory region
> in map_mmio_regions function.
> 
> I was able to fix issue in Dom0 by setting p2m_mmio_direct_nc_x type for the
> reserved memory in map_regions_p2mt, which is used to map memory during
> Dom0 creation.
> Patch can be found below.
> 
> Based on initial discussions on IRC channel - XN bit did the trick because 
> looks
> like vpu decoder is executing some code from this memory.
> 
> The purpose of this email is to discuss this issue and probably produce 
> generic
> solution for it.
> 
> Best regards,
> Oleksii.
> 
> ---
> arm: Set p2m_type to p2m_mmio_direct_nc_x for reserved memory regions
> 
> This is the enhancement of the
> 46b3dd3718144ca6ac2c12a3b106e57fb7156554.
> Those patch introduces p2m_mmio_direct_nc_x p2m type which sets the
> e->p2m.xn = 0 for the reserved-memory, such as vpu encoder/decoder.
> 
> Set p2m_mmio_direct_nc_x in map_regions_p2mt for reserved-memory the
> same way it does in map_mmio_regions. This change is for the case when vpu
> encoder/decoder works in DomO and not passed-through to the Guest
> Domains.

For Dom0, there is no SMMU, so no need x. Just nc is enough.

Regards,
Peng.

> 
> Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@xxxxxxxx>
> ---
>  xen/arch/arm/p2m.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index
> e9568dab88..bb1f681b71 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1333,6 +1333,13 @@ int map_regions_p2mt(struct domain *d,
>                       mfn_t mfn,
>                       p2m_type_t p2mt)
>  {
> +    if (((long)gfn_x(gfn) >= (GUEST_RAM0_BASE >> PAGE_SHIFT)) &&
> +        (((long)gfn_x(gfn) + nr) <=
> +        ((GUEST_RAM0_BASE + GUEST_RAM0_SIZE)>> PAGE_SHIFT)))
> +    {
> +        p2m_remove_mapping(d, gfn, nr, mfn);
> +        return p2m_insert_mapping(d, gfn, nr, mfn,
> p2m_mmio_direct_nc_x);
> +    }
>      return p2m_insert_mapping(d, gfn, nr, mfn, p2mt);  }
> 
> --
> 2.27.0