Re: [PATCH 05/11] x86: remove HIGHMEM64G support

[Mike Rapoport <rppt@kernel.org>]

On Fri, Apr 11, 2025 at 04:44:13PM -0700, Dave Hansen wrote:
> Has anyone run into any problems on 6.15-rc1 with this stuff?
> 
> 0xf75fe000 is the mem_map[] entry for the first page >4GB. It obviously
> wasn't allocated, thus the oops. Looks like the memblock for the >4GB
> memory didn't get removed although the pgdats seem correct.

That's apparently because of 6faea3422e3b ("arch, mm: streamline HIGHMEM
freeing"). 
Freeing of high memory was clamped to the end of ZONE_HIGHMEM which is 4G
and after 6faea3422e3b there's no more clamping, so memblock_free_all()
tries to free memory >4G as well.
 
> I'll dig into it some more. Just wanted to make sure there wasn't a fix
> out there already.

This should fix it.

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 57120f0749cc..4b24c0ccade4 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1300,6 +1300,8 @@ void __init e820__memblock_setup(void)
 		memblock_add(entry->addr, entry->size);
 	}
 
+	memblock_remove(PFN_PHYS(max_pfn), -1);
+
 	/* Throw away partial pages: */
 	memblock_trim_memory(PAGE_SIZE);
 
> The way I'm triggering this is booting qemu with a 32-bit PAE kernel,
> and "-m 4096" (or more).
> 
> > [    0.003806] Warning: only 4GB will be used. Support for for CONFIG_HIGHMEM64G was removed!
> ...
> > [    0.561310] BUG: unable to handle page fault for address: f75fe000
> > [    0.562226] #PF: supervisor write access in kernel mode
> > [    0.562947] #PF: error_code(0x0002) - not-present page
> > [    0.563653] *pdpt = 0000000002da2001 *pde = 000000000300c067 *pte = 0000000000000000 
> > [    0.564728] Oops: Oops: 0002 [#1] SMP NOPTI
> > [    0.565315] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.15.0-rc1-00288-ge618ee89561b-dirty #311 PREEMPT(undef) 
> > [    0.567428] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > [    0.568777] EIP: __free_pages_core+0x3c/0x74
> > [    0.569378] Code: c3 d3 e6 83 ec 10 89 44 24 08 89 74 24 04 c7 04 24 c6 32 3a c2 89 55 f4 e8 a9 11 45 fe 85 f6 8b 55 f4 74 19 89 d8 31 c9 66 90 <0f> ba 30 0d c7 40 1c 00 00 00 00 41 83 c0 28 39 ce 75 ed 8b 03 c1
> > [    0.571943] EAX: f75fe000 EBX: f75fe000 ECX: 00000000 EDX: 0000000a
> > [    0.572806] ESI: 00000400 EDI: 00500000 EBP: c247becc ESP: c247beb4
> > [    0.573776] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00210046
> > [    0.574606] CR0: 80050033 CR2: f75fe000 CR3: 02da6000 CR4: 000000b0
> > [    0.575464] Call Trace:
> > [    0.575816]  memblock_free_pages+0x11/0x2c
> > [    0.576392]  memblock_free_all+0x2ce/0x3a0
> > [    0.576955]  mm_core_init+0xf5/0x320
> > [    0.577423]  start_kernel+0x296/0x79c
> > [    0.577950]  ? set_init_arg+0x70/0x70
> > [    0.578478]  ? load_ucode_bsp+0x13c/0x1a8
> > [    0.579059]  i386_start_kernel+0xad/0xb0
> > [    0.579614]  startup_32_smp+0x151/0x154
> > [    0.580100] Modules linked in:
> > [    0.580358] CR2: 00000000f75fe000
> > [    0.580630] ---[ end trace 0000000000000000 ]---
> > [    0.581111] EIP: __free_pages_core+0x3c/0x74
> > [    0.581455] Code: c3 d3 e6 83 ec 10 89 44 24 08 89 74 24 04 c7 04 24 c6 32 3a c2 89 55 f4 e8 a9 11 45 fe 85 f6 8b 55 f4 74 19 89 d8 31 c9 66 90 <0f> ba 30 0d c7 40 1c 00 00 00 00 41 83 c0 28 39 ce 75 ed 8b 03 c1
> > [    0.584767] EAX: f75fe000 EBX: f75fe000 ECX: 00000000 EDX: 0000000a
> > [    0.585651] ESI: 00000400 EDI: 00500000 EBP: c247becc ESP: c247beb4
> > [    0.586530] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00210046
> > [    0.587480] CR0: 80050033 CR2: f75fe000 CR3: 02da6000 CR4: 000000b0
> > [    0.588344] Kernel panic - not syncing: Attempted to kill the idle task!
> > [    0.589435] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
> 
> > [    0.561310] BUG: unable to handle page fault for address: f75fe000
> > [    0.562226] #PF: supervisor write access in kernel mode
> > [    0.562947] #PF: error_code(0x0002) - not-present page
> > [    0.563653] *pdpt = 0000000002da2001 *pde = 000000000300c067 *pte = 0000000000000000 
> > [    0.564728] Oops: Oops: 0002 [#1] SMP NOPTI
> > [    0.565315] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.15.0-rc1-00288-ge618ee89561b-dirty #311 PREEMPT(undef) 
> > [    0.567428] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > [    0.568777] EIP: __free_pages_core+0x3c/0x74
> > [    0.569378] Code: c3 d3 e6 83 ec 10 89 44 24 08 89 74 24 04 c7 04 24 c6 32 3a c2 89 55 f4 e8 a9 11 45 fe 85 f6 8b 55 f4 74 19 89 d8 31 c9 66 90 <0f> ba 30 0d c7 40 1c 00 00 00 00 41 83 c0 28 39 ce 75 ed 8b 03 c1
> > [    0.571943] EAX: f75fe000 EBX: f75fe000 ECX: 00000000 EDX: 0000000a
> > [    0.572806] ESI: 00000400 EDI: 00500000 EBP: c247becc ESP: c247beb4
> > [    0.573776] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00210046
> > [    0.574606] CR0: 80050033 CR2: f75fe000 CR3: 02da6000 CR4: 000000b0
> > [    0.575464] Call Trace:
> > [    0.575816]  memblock_free_pages+0x11/0x2c
> > [    0.576392]  memblock_free_all+0x2ce/0x3a0
> > [    0.576955]  mm_core_init+0xf5/0x320
> > [    0.577423]  start_kernel+0x296/0x79c
> > [    0.577950]  ? set_init_arg+0x70/0x70
> > [    0.578478]  ? load_ucode_bsp+0x13c/0x1a8
> > [    0.579059]  i386_start_kernel+0xad/0xb0
> > [    0.579614]  startup_32_smp+0x151/0x154
> > [    0.580100] Modules linked in:
> > [    0.580358] CR2: 00000000f75fe000
> > [    0.580630] ---[ end trace 0000000000000000 ]---
> > [    0.581111] EIP: __free_pages_core+0x3c/0x74
> > [    0.581455] Code: c3 d3 e6 83 ec 10 89 44 24 08 89 74 24 04 c7 04 24 c6 32 3a c2 89 55 f4 e8 a9 11 45 fe 85 f6 8b 55 f4 74 19 89 d8 31 c9 66 90 <0f> ba 30 0d c7 40 1c 00 00 00 00 41 83 c0 28 39 ce 75 ed 8b 03 c1
> > [    0.584767] EAX: f75fe000 EBX: f75fe000 ECX: 00000000 EDX: 0000000a
> > [    0.585651] ESI: 00000400 EDI: 00500000 EBP: c247becc ESP: c247beb4
> > [    0.586530] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00210046
> > [    0.587480] CR0: 80050033 CR2: f75fe000 CR3: 02da6000 CR4: 000000b0
> > [    0.588344] Kernel panic - not syncing: Attempted to kill the idle task!
> > [    0.589435] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

-- 
Sincerely yours,
Mike.