bug in identity map for 4KB pages?

[Ard Biesheuvel]

On 29 July 2015 at 04:37, Stuart Yoder <stuart.yoder at freescale.com> wrote:
> Our system has RAM at a high address, and previously required using 48-bit VA
> in order to have an idmap that covered all of RAM.
>
> In testing on 4.2-rc4, which now contains support for the increased VA range
> of the idmap without using 48-bit VA, I'm finding that things work for
> 64KB pages, but do not for 4KB pages.
>
> Is there any known limitation here with 4KB pages?  Any ideas?
>

You probably have memory at 0x8000_0000 and at 0x80_8000_0000, right?
So the physical arrangement still requires more than the 39 bits of
virtual address space you get with 3 levels, even if the ID map can
cope now. That is why you get the 0x40_0000_0000 virtual address:
__phys_to_virt() just wraps to a positive number.

-- 
Ard.


> ------------------------------------------------------------------------------
>
> Booting Linux on physical CPU 0x0
> Initializing cgroup subsys cpu
> Linux version 4.2.0-rc4+ (b08248 at right) (gcc version 4.8.3 20131202 (prerelease) (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro GCC 2013.11) ) #180 SMP PREEMPT Tue Jul 28 20:51:47 CDT 2015
> CPU: AArch64 Processor [411fd071] revision 1
> Detected PIPT I-cache on CPU0
> alternatives: enabling workaround for ARM erratum 832075
> alternatives: detected feature GIC system register CPU interface
> earlycon: Early serial console at MMIO 0x21c0600 (options '115200')
> bootconsole [uart0] enabled
> efi: Getting EFI parameters from FDT:
> efi: UEFI not found.
> cma: Reserved 16 MiB at 0x00000000fec00000
> BUG: not creating mapping for 0x0000008080000000 at 0x0000004000000000 - outside kernel range
> Unable to handle kernel paging request at virtual address 435ffff000
> pgd = ffffffc000924000
> [435ffff000] *pgd=0000000000000000, *pud=0000000000000000
> Internal error: Oops: 96000045 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 4.2.0-rc4+ #180
> Hardware name: Freescale Layerscape 2085a software Simulator model (DT)
> task: ffffffc00088cc70 ti: ffffffc000880000 task.ti: ffffffc000880000
> PC is at memset+0x16c/0x1c0
> LR is at early_alloc+0x70/0x80
> pc : [<ffffffc0003250ac>] lr : [<ffffffc00080de50>] pstate: 400002c5
> sp : ffffffc000883ea0
> x29: ffffffc000883ea0 x28: 00000000a00000dc
> x27: ffffffc000081198 x26: 00000083e0000000
> x25: ffffffc000000000 x24: ffffffc00089a000
> x23: 0000000000000018 x22: 00000000c0000000
> x21: 0000008080000000 x20: 000000435ffff000
> x19: 0000000000001000 x18: 0000000000000000
> x17: 0000000000000006 x16: 00000083e0000000
> x15: 0000000000000018 x14: 0000008080000000
> x13: ffffffc000900dd0 x12: 0000000000000578
> x11: 0000000600000000 x10: 00000083dffff000
> x9 : 0000000000000000 x8 : 000000435ffff000
> x7 : 0000000000000000 x6 : 000000000000003f
> x5 : 0000000000000040 x4 : 0000000000000000
> x3 : 0000000000000004 x2 : 0000000000000fc0
> x1 : 0000000000000000 x0 : 000000435ffff000
>
> Process swapper (pid: 0, stack limit = 0xffffffc000880020)
> Stack: (0xffffffc000883ea0 to 0xffffffc000884000)
> 3ea0: 00883ec0 ffffffc0 0080df60 ffffffc0 00900200 ffffffc0 00886000 ffffffc0
> 3ec0: 00883f20 ffffffc0 0080b7ac ffffffc0 00080000 ffffffc0 fa9fa000 ffffffbf
> 3ee0: 00000040 00000000 00000000 00000000 00886000 ffffffc0 80000000 00000000
> 3f00: 80921000 00000000 80924000 00000000 00000040 00000000 fa9fa000 ffffffbf
> 3f20: 00883fa0 ffffffc0 00809690 ffffffc0 00000001 00000000 0083c120 ffffffc0
> 3f40: 9fffa000 00000000 00000000 00000000 00886000 ffffffc0 80000000 00000000
> 3f60: 80921000 00000000 80924000 00000000 00000001 00000000 9fffa000 00000000
> 3f80: 00000000 00000000 00000000 80000000 00000080 00000000 64667467 ff616b73
> 3fa0: 00000000 00000000 805d3000 00000000 fff9fa40 00000000 00000e12 00000000
> 3fc0: 9fffa000 00000000 00000000 00000000 00000000 00000000 80000000 00000000
> 3fe0: 00000000 00000000 0083c948 ffffffc0 00000000 00000000 00000000 00000000
> Call trace:
> [<ffffffc0003250ac>] memset+0x16c/0x1c0
> [<ffffffc00080df5c>] paging_init+0xd0/0x174
> [<ffffffc00080b7a8>] setup_arch+0x28c/0x5c4
> [<ffffffc00080968c>] start_kernel+0x94/0x3d0
> Code: 91010108 54ffff4a 8b040108 cb050042 (d50b7428)
> ---[ end trace cb88537fdc8fa200 ]---
> Kernel panic - not syncing: Attempted to kill the idle task!
> ---[ end Kernel panic - not syncing: Attempted to kill the idle task!