mm/debug_vm_pgtable.c:860 warning triggered

["Daniel Walker (danielwa)" <danielwa@cisco.com>]

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Hi,

This warning has triggered on our powerpc equipment.

debug_vm_pgtable: [debug_vm_pgtable         ]: Validating architecture page table helpers
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at mm/debug_vm_pgtable.c:860 0xc1012190
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Not tainted 6.6.0 #14
Hardware name: MPC8544DS e500v2 0x80210030 MPC8544 DS
NIP:  c1012190 LR: c101216c CTR: 00000000
REGS: c145bc70 TRAP: 0700   Not tainted  (6.6.0)
MSR:  00029000 <CE,EE,ME>  CR: 48000248  XER: 00000000

GPR00: c1012094 c145bd60 c1498000 c145bd6c 0000003c 00000000 7cffffff 00000001 
GPR08: efa2d000 00000000 00000000 2d589a6c 88000248 00000000 c000343c 00000000 
GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 c10000d8 
GPR24: 00000000 00000000 00000000 00000000 00000000 00000200 fffffffc 7cffffff 
Call Trace:
[c145bd60] [c1012094] 0xc1012094 (unreliable)
[c145be30] [c0003044] 0xc0003044
[c145bea0] [c1000ea0] 0xc1000ea0
[c145bee0] [c0003460] 0xc0003460
[c145bf00] [c0011224] 0xc0011224
--- interrupt: 0 at 0x00000000
NIP:  00000000 LR: 00000000 CTR: 00000000
REGS: c145bf10 TRAP: 0000   Not tainted  (6.6.0)
MSR:  00000000 <>  CR: 00000000  XER: 00000000

GPR00: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
GPR08: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
GPR16: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
GPR24: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 
--- interrupt: 0
Code: 3861000c 38a00000 4b10a235 8121000c 7c1f4800 41820008 0fe00000 8121006c 7d29e378 5529463e 7c1d4840 41820008 <0fe00000> 81410080 2c0affff 41820058 
---[ end trace 0000000000000000 ]---

This appears to be the following code,

 850 
 851 static void __init pte_swap_tests(struct pgtable_debug_args *args)
 852 {
 853         swp_entry_t swp;
 854         pte_t pte;
 855 
 856         pr_debug("Validating PTE swap\n");
 857         pte = pfn_pte(args->fixed_pte_pfn, args->page_prot);
 858         swp = __pte_to_swp_entry(pte);
 859         pte = __swp_entry_to_pte(swp);
 860         WARN_ON(args->fixed_pte_pfn != pte_pfn(pte));
 861 }
 862 


This only happens in powerpc with the following config options enabled,

CONFIG_PTE_64BIT=y
CONFIG_PHYS_64BIT=y

These options can increase the pte_t type to 64bits, which swp_entry_t remains unsigned
long which is 32 bits on there systems. This warning appears to have triggered since the
inclusion of CONFIG_DEBUG_VM_PGTABLE support for powerpc.

To reproduce the issue you can use the attached config to build a powerpc kernel. Then
boot with QEMU using the following command line.

qemu-system-ppc -M mpc8544ds -kernel ../powerpc/vmlinux -append "console=ttyS0" -nographic

Please CC me on any fixes in the future.

Thanks,

Daniel


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