Re: [PATCH v3] powerpc/memhotplug: Add add_pages override for PPC

[Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>]

On 6/29/22 12:00 PM, Kefeng Wang wrote:
> Hi,
> 
> On 2022/6/29 13:09, Aneesh Kumar K.V wrote:
>> 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@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@huawei.com>
>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>> Changes from v2:
>> * drop WARN_ON_ONCE
>> * check for error from __add_pages
>>
>>   arch/powerpc/Kconfig  |  4 ++++
>>   arch/powerpc/mm/mem.c | 33 ++++++++++++++++++++++++++++++++-
>>   2 files changed, 36 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index c2ce2e60c8f0..7aa12e88c580 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -358,6 +358,10 @@ config ARCH_SUSPEND_NONZERO_CPU
>>       def_bool y
>>       depends on PPC_POWERNV || PPC_PSERIES
>>   +config ARCH_HAS_ADD_PAGES
>> +    def_bool y
>> +    depends on ARCH_ENABLE_MEMORY_HOTPLUG
>> +
>>   config PPC_DCR_NATIVE
>>       bool
>>   diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
>> index 52b77684acda..a97128a48817 100644
>> --- a/arch/powerpc/mm/mem.c
>> +++ b/arch/powerpc/mm/mem.c
>> @@ -105,6 +105,37 @@ 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;
>                 int ret = -EINVAL;
>> +
>> +    ret = __add_pages(nid, start_pfn, nr_pages, params);
>> +    if (ret)
>> +        return ret;
>> +

considering we are updating ret immediately why should we initialize that to EINVAL?

	int ret = -EINVAL;
	ret = __add_pages(nid, start_pfn, nr_pages, params);
	


>> +    /* update max_pfn, max_low_pfn and high_memory */
>> +    update_end_of_memory_vars(start_pfn << PAGE_SHIFT,
>> +                  nr_pages << PAGE_SHIFT);
>> +
>> +    return ret;
>> +}
>> +
> and could we only call update_end_of_memory_vars() in arch_add_memory()?
>>   int __ref arch_add_memory(int nid, u64 start, u64 size,
>>                 struct mhp_params *params)
>>   {
>> @@ -115,7 +146,7 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
>>       rc = arch_create_linear_mapping(nid, start, size, params);
>>       if (rc)
>>           return rc;
>> -    rc = __add_pages(nid, start_pfn, nr_pages, params);
>> +    rc = add_pages(nid, start_pfn, nr_pages, params);
>>       if (rc)
>>           arch_remove_linear_mapping(start, size);
> 
> if (!rc)
> 
>     update_end_of_memory_vars(start_pfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT);
> 
> else
> 
>     arch_remove_linear_mapping(start, size);
> 
> Thanks
> 

commit 3072e413e305 goes into the details of why it is done in add_pages

mm/memory_hotplug: introduce add_pages

There are new users of memory hotplug emerging.  Some of them require
different subset of arch_add_memory.  There are some which only require
allocation of struct pages without mapping those pages to the kernel
address space.  We currently have __add_pages for that purpose.  But this
is rather lowlevel and not very suitable for the code outside of the
memory hotplug.  E.g.  x86_64 wants to update max_pfn which should be done
by the caller.  Introduce add_pages() which should care about those
details if they are needed.  Each architecture should define its
implementation and select CONFIG_ARCH_HAS_ADD_PAGES.  All others use the
currently existing __add_pages.

We could debate whether max_pfn/high_memory should encompass device private memory too.
But the current code on x86 does that and I would also expect virt_addr_valid to return
true for the address mapping private device memory. 



>>       return rc;