Re: [PATCH v2 3/3] powerpc/mm/cxl: Add the fault handling cpu to mm cpumask

[Frederic Barrat <fbarrat@linux.vnet.ibm.com>]

Le 01/06/2017 à 16:33, Aneesh Kumar K.V a écrit :
> We use mm cpumask for serializing against lockless page table walk. Anybody
> who is doing a lockless page table walk is expected to disable irq and only
> cpus in mm cpumask is expected do the lockless walk. This ensure that
> a THP split can send IPI to only cpus in the mm cpumask, to make sure there
> are no parallel lockless page table walk.
> 
> Add the CAPI fault handling cpu to the mm cpumask so that we can do the lockless
> page table walk while inserting hash page table entries.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---


Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>



>   arch/powerpc/mm/pgtable-book3s64.c | 10 +---------
>   drivers/misc/cxl/fault.c           |  6 ++++++
>   2 files changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
> index 2679f57b90e2..6a50ab23f722 100644
> --- a/arch/powerpc/mm/pgtable-book3s64.c
> +++ b/arch/powerpc/mm/pgtable-book3s64.c
> @@ -83,15 +83,7 @@ static void do_nothing(void *unused)
>   void serialize_against_pte_lookup(struct mm_struct *mm)
>   {
>   	smp_mb();
> -	/*
> -	 * Cxl fault handling requires us to do a lockless page table
> -	 * walk while inserting hash page table entry with mm tracked
> -	 * in cxl context. Hence we need to do a global flush.
> -	 */
> -	if (cxl_ctx_in_use())
> -		smp_call_function(do_nothing, NULL, 1);
> -	else
> -		smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1);
> +	smp_call_function_many(mm_cpumask(mm), do_nothing, NULL, 1);
>   }
> 
>   /*
> diff --git a/drivers/misc/cxl/fault.c b/drivers/misc/cxl/fault.c
> index 5344448f514e..02efaaa7cbd1 100644
> --- a/drivers/misc/cxl/fault.c
> +++ b/drivers/misc/cxl/fault.c
> @@ -140,6 +140,12 @@ static void cxl_handle_page_fault(struct cxl_context *ctx,
>   	unsigned long access, flags, inv_flags = 0;
> 
>   	trace_cxl_pte_miss(ctx, dsisr, dar);
> +	/*
> +	 * Add the fault handling cpu to task mm cpumask so that we
> +	 * can do a safe lockless page table walk when inserting the
> +	 * hash page table entry.
> +	 */
> +	cpumask_set_cpu(smp_processor_id(), mm_cpumask(mm));
> 
>   	if ((result = copro_handle_mm_fault(mm, dar, dsisr, &flt))) {
>   		pr_devel("copro_handle_mm_fault failed: %#x\n", result);
>