Re: [Xen-devel] EFI boot Issue with setup_xenheap_mappings()

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-10-08 at 18:58 -0500, Suravee Suthikulanit wrote:

Adding Vijay who raised what seems to be the same issue yesterday.

> Hi All,
> 
> After we resolved the flushing and tlbi issues previously discussed, I 
> ran into a couple more issues. Please note that the available memory 
> regions retrieved from EFI system table are:
> 
> (XEN) RAM: 0000008001000000 - 0000008007ffdfff <- (1)
> (XEN) RAM: 0000008007ffe000 - 0000008007ffffff
> (XEN) RAM: 0000008008000000 - 000000801fffdfff
> (XEN) RAM: 000000801fffe000 - 000000801fffffff
> (XEN) RAM: 0000008020000000 - 000000802fffffff
> (XEN) RAM: 0000008030001000 - 00000083f0ffffff
> (XEN) RAM: 00000083f1000000 - 00000083f101ffff
> (XEN) RAM: 00000083f1020000 - 00000083fbbb1fff
> (XEN) RAM: 00000083fc4b8000 - 00000083fc4b8fff
> (XEN) RAM: 00000083fc6a4000 - 00000083fec25fff
> (XEN) RAM: 00000083fec26000 - 00000083fee8bfff
> (XEN) RAM: 00000083fee8c000 - 00000083ff225fff
> (XEN) RAM: 00000083ff226000 - 00000083ff263fff
> (XEN) RAM: 00000083ff265000 - 00000083ff2c4fff
> (XEN) RAM: 00000083ffe70000 - 00000083ffffffff
> 
> Note:
> (1) Physical memory actually started at 0x80_0000_0000, the first 16MB 
> is used by UEFI.
> 
> ISSUE 1:
> Data abort is happening at:
>    start_xen()
>      -> setup_mm()
>        -> init_boot_pages()
>          -> bootmem_region_add()
>            -> Accessing bootmem_region_list causing data abort !!!
> 
> bootmem_region_list is initialized by "init_boot_pages()" at the first 
> calling of "bootmem_region_add()". It points to VA 0x800000000000, which 
> is at the beginning of the 1:1 mapping of RAM region (slots 256) (see 
> include/asm-arm/config.h for complete ARM64 memory layout).
> 
> So, I looked at how the page table is setup for this region. This is 
> done at the following place:
>    start_xen()
>      -> setup_mm()
>        -> setup_xenheap_mappings(bank_start>>PAGE_SHIFT, 
> bank_size>>PAGE_SHIFT)
> 
> Inside setup_xenheap_mapping():
>    offset = pfn_to_pdx(base_mfn - xenheap_mfn_start).
>      where:
>        base_mfn          = 0x8000000
>        xenheap_mfn_start = 0x8010000
> 
> This results in the math above to fail, and resulting in invalid offset, 
> invalid vaddr, and invalid pte for this region.
> 
> So, I put a hack where I set base_mfn and xenheap_mfn_start to 0x8010000 
> in the code above (not sure if this is the right things to do), and this 
> seems to resolve issue 1  continue all the way to 
> setup_frame_table_mapping().

Yes, looking again at the arm64 setup_xenheap_mapping I think it is
pretty broken when facing non-aligned memory. I think it's just a
coincidence that EFI happens to expose this (by reserving/fragmenting
more memory), where u-boot based systems tend not to do so much of that
sort of thing.

Setting both base_mfn and xenheap_mfn_start to the aligned address seems
likely to be the correct path forward. I think though some care may need
to be taken with maddr_to_virt at the same time, since we need to
arrange for any offset in the frametable to match the offset in the
xenheap mapping (which is what I think I was trying to do with the
existing broken code).

virt_to_maddr uses a h/w pt walk, so should be find whatever we do.

> ISSUE 2:
> Here, it is also getting data abort when accessing frame_table (at 
> 0x800000000 = 32GB). It seems that the page table for this region is 
> also messed up.

It's quite possible this is broken too, or this could potentially be
fallout from the mismatch I mention above.

> Need a break and more investigation at this point.

I'm going to have a look this morning.

Ian.


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