BUG() at boot in __phys_addr with DEBUG_VIRTUAL

[Dave Hansen]

I'm seeing a BUG() at boot in __phys_addr when it has DEBUG_VIRTUAL enabled:

>> [    1.193264] ------------[ cut here ]------------
>> [    1.198502] kernel BUG at /home/davehans/linux.git/arch/x86/mm/physaddr.c:36!
> ...
>> [    1.368810] Call Trace:
>> [    1.371590]  [<ffffffff8105824c>] __change_page_attr_set_clr+0x42c/0xff0
>> [    1.379197]  [<ffffffff81059e42>] kernel_map_pages_in_pgd+0x72/0x110
>> [    1.386410]  [<ffffffff81fe2be2>] __map_region+0x45/0x63
>> [    1.392437]  [<ffffffff81fe2e13>] efi_map_region+0x32/0xce
>> [    1.398663]  [<ffffffff81fe2936>] efi_enter_virtual_mode+0x18c/0x3a4
>> [    1.405876]  [<ffffffff81fcb0b6>] start_kernel+0x421/0x4a1
>> [    1.412101]  [<ffffffff81fcaa85>] ? set_init_arg+0x55/0x55
>> [    1.418327]  [<ffffffff81fca120>] ? early_idt_handlers+0x120/0x120
>> [    1.425342]  [<ffffffff81fca5f2>] x86_64_start_reservations+0x2a/0x2c
>> [    1.432652]  [<ffffffff81fca746>] x86_64_start_kernel+0x152/0x161
>> [    1.439565] Code: 0f 94 c2 31 c0 e8 a6 47 83 00 48 c7 c7 41 49 cc 81 31 c0 e8 98 47 83 00 31 d2 be 01 00 00 00 48 c7 c7 a0 49 f2 81 e8 ab 4a 0e 00 <0f> 0b 0f 0b 4c 89 e2 48 c7 c6 b3 e5 a0 81 48 c7 c7 5c 7a ca 81 
>> [    1.461866] RIP  [<ffffffff8105c055>] __phys_addr+0x185/0x260
>> [    1.468400]  RSP <ffffffff81e03cf8>
>> [    1.472396] ---[ end trace b59b0f17341a4bc4 ]---
>> [    1.477663] Kernel panic - not syncing: Attempted to kill the idle task!
>> [    1.485270] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!

But I've noticed something odd.  kernel_map_pages_in_pgd() takes a pfn:

extern int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long
			address, unsigned numpages, unsigned long
			page_flags);

But the code in arch/x86/platform/efi/efi_64.c seems a bit confused
about that.  Two users pass a physical address while a third passes in a
pfn:

>         if (kernel_map_pages_in_pgd(pgd, text >> PAGE_SHIFT, text, npages, 0)) {
>         if (kernel_map_pages_in_pgd(pgd, md->phys_addr, va, md->num_pages, pf))
>         if (kernel_map_pages_in_pgd(pgd, pa_memmap, pa_memmap, num_pages, _PAGE_NX)) {

kernel_map_pages_in_pgd() also sticks that value in to 'struct
cpa_data'->pfn.  But, then the "PFN" seems to get used like a physical
address.  For instance:

                set_pmd(pmd, __pmd(cpa->pfn | _PAGE_PSE | ...

How could this possibly work?
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