[PATCH V2] powerpc/memhotplug: Add add_pages override for PPC

[Michael Ellerman]

"Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> writes:
> With commit ffa0b64e3be5 ("powerpc: Fix virt_addr_valid() for 64-bit Book3E & 32-bit")
> the kernel now validate the addr against high_memory value. This results
> in the below BUG_ON with dax pfns.
>
> [  635.798741][T26531] kernel BUG at mm/page_alloc.c:5521!
> 1:mon> e
> cpu 0x1: Vector: 700 (Program Check) at [c000000007287630]
>     pc: c00000000055ed48: free_pages.part.0+0x48/0x110
>     lr: c00000000053ca70: tlb_finish_mmu+0x80/0xd0
>     sp: c0000000072878d0
>    msr: 800000000282b033
>   current = 0xc00000000afabe00
>   paca    = 0xc00000037ffff300   irqmask: 0x03   irq_happened: 0x05
>     pid   = 26531, comm = 50-landscape-sy
> kernel BUG at :5521!
> Linux version 5.19.0-rc3-14659-g4ec05be7c2e1 (kvaneesh at ltc-boston8) (gcc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #625 SMP Thu Jun 23 00:35:43 CDT 2022
> 1:mon> t
> [link register   ] c00000000053ca70 tlb_finish_mmu+0x80/0xd0
> [c0000000072878d0] c00000000053ca54 tlb_finish_mmu+0x64/0xd0 (unreliable)
> [c000000007287900] c000000000539424 exit_mmap+0xe4/0x2a0
> [c0000000072879e0] c00000000019fc1c mmput+0xcc/0x210
> [c000000007287a20] c000000000629230 begin_new_exec+0x5e0/0xf40
> [c000000007287ae0] c00000000070b3cc load_elf_binary+0x3ac/0x1e00
> [c000000007287c10] c000000000627af0 bprm_execve+0x3b0/0xaf0
> [c000000007287cd0] c000000000628414 do_execveat_common.isra.0+0x1e4/0x310
> [c000000007287d80] c00000000062858c sys_execve+0x4c/0x60
> [c000000007287db0] c00000000002c1b0 system_call_exception+0x160/0x2c0
> [c000000007287e10] c00000000000c53c system_call_common+0xec/0x250
>
> The fix is to make sure we update high_memory on memory hotplug.
> This is similar to what x86 does in commit 3072e413e305 ("mm/memory_hotplug: introduce add_pages")
>
> Fixes: ffa0b64e3be5 ("powerpc: Fix virt_addr_valid() for 64-bit Book3E & 32-bit")
> Cc: Kefeng Wang <wangkefeng.wang at huawei.com>
> Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
 
...

> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 52b77684acda..2a63920c369d 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -105,6 +105,36 @@ void __ref arch_remove_linear_mapping(u64 start, u64 size)
>  	vm_unmap_aliases();
>  }
>  
> +/*
> + * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
> + * updating.
> + */
> +static void update_end_of_memory_vars(u64 start, u64 size)
> +{
> +	unsigned long end_pfn = PFN_UP(start + size);
> +
> +	if (end_pfn > max_pfn) {
> +		max_pfn = end_pfn;
> +		max_low_pfn = end_pfn;
> +		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
> +	}
> +}
> +
> +int __ref add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
> +		    struct mhp_params *params)
> +{
> +	int ret;
> +
> +	ret = __add_pages(nid, start_pfn, nr_pages, params);
> +	WARN_ON_ONCE(ret);

What's the justification for making this a WARN_ON_ONCE(), and then
continuing to update the variables anyway?

I realise that's what x86 does, but it seems kind of wrong.

cheers

> +	/* update max_pfn, max_low_pfn and high_memory */
> +	update_end_of_memory_vars(start_pfn << PAGE_SHIFT,
> +				  nr_pages << PAGE_SHIFT);
> +
> +	return ret;
> +}