[Xenial PATCH 2/3] UBUNTU: SAUCE: s390/mm: fix local TLB flushing vs. detach of an mm address space

Stefan Bader stefan.bader at canonical.com
Tue Sep 12 12:18:30 UTC 2017


On 12.09.2017 13:58, Colin Ian King wrote:
> On 12/09/17 10:45, Stefan Bader wrote:
>> From: Martin Schwidefsky <schwidefsky at de.ibm.com>
>>
>> BugLink: http://bugs.launchpad.net/bugs/1708399
>>
>> The local TLB flushing code keeps an additional mask in the mm.context,
>> the cpu_attach_mask. At the time a global flush of an address space is
>> done the cpu_attach_mask is copied to the mm_cpumask in order to avoid
>> future global flushes in case the mm is used by a single CPU only after
>> the flush.
>>
>> Trouble is that the reset of the mm_cpumask is racy against the detach
>> of an mm address space by switch_mm. The current order is first the
>> global TLB flush and then the copy of the cpu_attach_mask to the
>> mm_cpumask. The order needs to be the other way around.
>>
>> Cc: <stable at vger.kernel.org>
>> Reviewed-by: Heiko Carstens <heiko.carstens at de.ibm.com>
>> Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
>> (backported from b3e5dc45fd1ec2aa1de6b80008f9295eb17e0659 linux-next)
>> [merged with "s390/mm,kvm: flush gmap address space with IDTE"]
>> Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
>> ---
>>  arch/s390/include/asm/tlbflush.h | 56 ++++++++++++----------------------------
>>  1 file changed, 16 insertions(+), 40 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/tlbflush.h b/arch/s390/include/asm/tlbflush.h
>> index 80868c84..d54cc83 100644
>> --- a/arch/s390/include/asm/tlbflush.h
>> +++ b/arch/s390/include/asm/tlbflush.h
>> @@ -47,47 +47,31 @@ static inline void __tlb_flush_global(void)
>>  }
>>  
>>  /*
>> - * Flush TLB entries for a specific mm on all CPUs (in case gmap is used
>> - * this implicates multiple ASCEs!).
>> + * Flush TLB entries for a specific ASCE on all CPUs.
>>   */
>> -static inline void __tlb_flush_full(struct mm_struct *mm)
>> +static inline void __tlb_flush_mm(struct mm_struct * mm)
>>  {
>> +	/*
>> +	 * If the machine has IDTE we prefer to do a per mm flush
>> +	 * on all cpus instead of doing a local flush if the mm
>> +	 * only ran on the local cpu.
>> +	 */
>>  	preempt_disable();
>>  	atomic_add(0x10000, &mm->context.attach_count);
>> -	if (cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
>> -		/* Local TLB flush */
>> -		__tlb_flush_local();
>> +	/* Reset TLB flush mask */
>> +	if (MACHINE_HAS_TLB_LC)
>> +		cpumask_copy(mm_cpumask(mm), &mm->context.cpu_attach_mask);
>> +	barrier();
>> +	if (MACHINE_HAS_IDTE && list_empty(&mm->context.gmap_list)) {
>> +		__tlb_flush_idte(mm->context.asce);
>>  	} else {
>>  		/* Global TLB flush */
>>  		__tlb_flush_global();
>> -		/* Reset TLB flush mask */
>> -		if (MACHINE_HAS_TLB_LC)
>> -			cpumask_copy(mm_cpumask(mm),
>> -				     &mm->context.cpu_attach_mask);
>>  	}
>>  	atomic_sub(0x10000, &mm->context.attach_count);
>>  	preempt_enable();
>>  }
>>  
>> -/*
>> - * Flush TLB entries for a specific ASCE on all CPUs. Should never be used
>> - * when more than one asce (e.g. gmap) ran on this mm.
>> - */
>> -static inline void __tlb_flush_asce(struct mm_struct *mm, unsigned long asce)
>> -{
>> -	preempt_disable();
>> -	atomic_add(0x10000, &mm->context.attach_count);
>> -	if (MACHINE_HAS_IDTE)
>> -		__tlb_flush_idte(asce);
>> -	else
>> -		__tlb_flush_global();
>> -	/* Reset TLB flush mask */
>> -	if (MACHINE_HAS_TLB_LC)
>> -		cpumask_copy(mm_cpumask(mm), &mm->context.cpu_attach_mask);
>> -	atomic_sub(0x10000, &mm->context.attach_count);
>> -	preempt_enable();
>> -}
>> -
>>  static inline void __tlb_flush_kernel(void)
>>  {
>>  	if (MACHINE_HAS_IDTE)
>> @@ -97,7 +81,6 @@ static inline void __tlb_flush_kernel(void)
>>  }
>>  #else
>>  #define __tlb_flush_global()	__tlb_flush_local()
>> -#define __tlb_flush_full(mm)	__tlb_flush_local()
>>  
>>  /*
>>   * Flush TLB entries for a specific ASCE on all CPUs.
>> @@ -111,21 +94,14 @@ static inline void __tlb_flush_kernel(void)
>>  {
>>  	__tlb_flush_local();
>>  }
>> -#endif
>>  
>>  static inline void __tlb_flush_mm(struct mm_struct * mm)
>>  {
>> -	/*
>> -	 * If the machine has IDTE we prefer to do a per mm flush
>> -	 * on all cpus instead of doing a local flush if the mm
>> -	 * only ran on the local cpu.
>> -	 */
>> -	if (MACHINE_HAS_IDTE && list_empty(&mm->context.gmap_list))
>> -		__tlb_flush_asce(mm, mm->context.asce);
>> -	else
>> -		__tlb_flush_full(mm);
>> +	__tlb_flush_local();
>>  }
>>  
>> +#endif
>> +
>>  static inline void __tlb_flush_mm_lazy(struct mm_struct * mm)
>>  {
>>  	if (mm->context.flush_mm) {
>>
> 
> Maybe I'm being a bit slow here, but I'm finding this hard to see how
> this is related to linux-next commit
> b3e5dc45fd1ec2aa1de6b80008f9295eb17e0659
> 
> Do you mind explaining this backport?

It is a merge with the other commit mentioned above. Not the most obvious but
since it comes from the s390x maintainers I crossed my eyes and hope.

-Stefan

> 
> Colin
> 


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