Re: [PATCH v10 2/7] powerpc/mce: Fix MCE handling for huge pages

[Santosh Sivaraj]

Hi Nick,

Nicholas Piggin <npiggin@xxxxxxxxx> writes:

> Santosh Sivaraj's on August 15, 2019 10:39 am:
>> From: Balbir Singh <bsingharora@xxxxxxxxx>
>> 
>> The current code would fail on huge pages addresses, since the shift would
>> be incorrect. Use the correct page shift value returned by
>> __find_linux_pte() to get the correct physical address. The code is more
>> generic and can handle both regular and compound pages.
>> 
>> Fixes: ba41e1e1ccb9 ("powerpc/mce: Hookup derror (load/store) UE errors")
>> Signed-off-by: Balbir Singh <bsingharora@xxxxxxxxx>
>> [arbab@xxxxxxxxxxxxx: Fixup pseries_do_memory_failure()]
>> Signed-off-by: Reza Arbab <arbab@xxxxxxxxxxxxx>
>> Co-developed-by: Santosh Sivaraj <santosh@xxxxxxxxxx>
>> Signed-off-by: Santosh Sivaraj <santosh@xxxxxxxxxx>
>> Tested-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx # v4.15+
>> ---
>>  arch/powerpc/include/asm/mce.h       |  2 +-
>>  arch/powerpc/kernel/mce_power.c      | 55 ++++++++++++++--------------
>>  arch/powerpc/platforms/pseries/ras.c |  9 ++---
>>  3 files changed, 32 insertions(+), 34 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/mce.h b/arch/powerpc/include/asm/mce.h
>> index a4c6a74ad2fb..f3a6036b6bc0 100644
>> --- a/arch/powerpc/include/asm/mce.h
>> +++ b/arch/powerpc/include/asm/mce.h
>> @@ -209,7 +209,7 @@ extern void release_mce_event(void);
>>  extern void machine_check_queue_event(void);
>>  extern void machine_check_print_event_info(struct machine_check_event *evt,
>>  					   bool user_mode, bool in_guest);
>> -unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr);
>> +unsigned long addr_to_phys(struct pt_regs *regs, unsigned long addr);
>>  #ifdef CONFIG_PPC_BOOK3S_64
>>  void flush_and_reload_slb(void);
>>  #endif /* CONFIG_PPC_BOOK3S_64 */
>> diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
>> index a814d2dfb5b0..e74816f045f8 100644
>> --- a/arch/powerpc/kernel/mce_power.c
>> +++ b/arch/powerpc/kernel/mce_power.c
>> @@ -20,13 +20,14 @@
>>  #include <asm/exception-64s.h>
>>  
>>  /*
>> - * Convert an address related to an mm to a PFN. NOTE: we are in real
>> - * mode, we could potentially race with page table updates.
>> + * Convert an address related to an mm to a physical address.
>> + * NOTE: we are in real mode, we could potentially race with page table updates.
>>   */
>> -unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
>> +unsigned long addr_to_phys(struct pt_regs *regs, unsigned long addr)
>>  {
>> -	pte_t *ptep;
>> -	unsigned long flags;
>> +	pte_t *ptep, pte;
>> +	unsigned int shift;
>> +	unsigned long flags, phys_addr;
>>  	struct mm_struct *mm;
>>  
>>  	if (user_mode(regs))
>> @@ -35,14 +36,21 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
>>  		mm = &init_mm;
>>  
>>  	local_irq_save(flags);
>> -	if (mm == current->mm)
>> -		ptep = find_current_mm_pte(mm->pgd, addr, NULL, NULL);
>> -	else
>> -		ptep = find_init_mm_pte(addr, NULL);
>> +	ptep = __find_linux_pte(mm->pgd, addr, NULL, &shift);
>>  	local_irq_restore(flags);
>> +
>>  	if (!ptep || pte_special(*ptep))
>>  		return ULONG_MAX;
>> -	return pte_pfn(*ptep);
>> +
>> +	pte = *ptep;
>> +	if (shift > PAGE_SHIFT) {
>> +		unsigned long rpnmask = (1ul << shift) - PAGE_SIZE;
>> +
>> +		pte = __pte(pte_val(pte) | (addr & rpnmask));
>> +	}
>> +	phys_addr = pte_pfn(pte) << PAGE_SHIFT;
>> +
>> +	return phys_addr;
>>  }
>
> This should remain addr_to_pfn I think. None of the callers care what
> size page the EA was mapped with. 'pfn' is referring to the Linux pfn,
> which is the small page number.
>
>   if (shift > PAGE_SHIFT)
>     return (pte_pfn(*ptep) | ((addr & ((1UL << shift) - 1)) >> PAGE_SHIFT);
>   else
>     return pte_pfn(*ptep);
>
> Something roughly like that, then you don't have to change any callers
> or am I missing something?

Here[1] you asked to return the real address rather than pfn, which all
callers care about. So made the changes accordingly.

[1] https://www.spinics.net/lists/kernel/msg3187658.html

Thanks,
Santosh
>
> Thanks,
> Nick