[Bug Report] kdump crashes after latest EFI memblock changes on arm64 machines with large number of CPUs

[will.deacon@arm.com (Will Deacon)]

On Fri, Nov 02, 2018 at 02:44:10AM +0530, Bhupesh Sharma wrote:
> With the latest EFI changes for memblock reservation across kdump
> kernel from Ard (Commit 71e0940d52e107748b270213a01d3b1546657d74
> ["efi: honour memory reservations passed via a linux specific config
> table"]), we hit a panic while trying to boot the kdump kernel on
> machines which have large number of CPUs.
> 
> I have a arm64 board which has 224 CPUS:
> # lscpu
> <..snip..>
> CPU(s):              224
> On-line CPU(s) list: 0-223
> <..snip..>
> 
> Here are the crash logs in the kdump kernel on this machine:
> 
> [    0.000000] Unable to handle kernel paging request at virtual
> address ffff80003ffe0000
> val____)nt EL), IL ata abort info:
> [    0.or: Oops: 960000inted 4.18.0+ #3
> [    0.000000] pstate: 20400089 (nzCv daIf +PAN -UAO)
> [    0.000000] pc : __memcpy+0x110/0x180
> [    0.000000] lr : memblock_double_array+0x240/0x348
> [    0.000000] sp : ffff0000092efc80 x28: 00000000bffe0000
> [    0.000000] x27: 0000000000001800 x26: ffff000009d59000
> [    0.000000] x25: ffff80003ffe0000 x24: 0000000000000000
> [    0.000000] x23: 0000000000010000 x22: ffff000009d594e8
> [    0.000000] x21: ffff000009d594f4 x20: ffff0000093c7268
> [    0.000000] x19: 0000000000000c00 x18: 0000000000000010
> [    0.000000] x17: 0000000000000000 x16: 0000000000000000
> [    0.000000] x15: ffffffffffffffff3: 0000000fc18d0000 x12: 0000000800000000
> [    0.000000] x11: 0000000000000018 x10: 00000000ddab9e18
> [    0.000000] x9 : 0000000800000000 x8 : 00000000000002c1
> [    0.000000] x7 : 0000000091b90000 x6 : ffff80003ffe0000
> [    0.000000] x5 : 0000000000000001 x4 : 0000000000000000
> [    0.000000] x3 : 0000000000000000 x2 : 0000000000000b80
> [    0.000000] x1 : ffff000009d59540 x0 : ffff80003ffe0000
> [    0.000000] Process swapper)
> [    0.000000] Call trace:
> [    0.000000]  __memcpy+0x110/0x180
> [    0.000000]  memblock_add_range+0x134/0x2e8
> [    0.000000]  memblock_reserve+0x70/0xb8
> [    0.000000]  memblock_alloc_base_nid+0x6c/0x88
> [    0.000000]  __memblock_alloc_base+0x3c/0x4c
> [    0.000000]  memblock_alloc_base+0x28/0x4c
> [    0.000000]  memblock_alloc+0x2c/0x38
> [    0.000000]  early_pgtable_alloc+0x20/0xb0

Hmm, so this seems to be the crux of the issue: early_pgtable_alloc() relies
on memblock to allocate page-table memory, but this can be called before the
linear mapping is up and running (or even as part of creating the linear
mapping itself!) so the use of __va in memblock_double_array() actually
returns an unmapped address.

So I guess we either need to implement early_pgtable_alloc() some other way
(how?) or get memblock_double_array() to use a fixmap if it's called too
early (yuck). Alternatively, would it be possible to postpone processing of
the EFI mem_reserve entries until after we've created the linear mapping?

Will