Re: [PATCH 20/27] Split init_new_context and destroy_context

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2009-10-21 at 17:03 +0200, Alexander Graf wrote:
> For KVM we need to allocate a new context id, but don't really care about
> all the mm context around it.
> 
> So let's split the alloc and destroy functions for the context id, so we can
> grab one without allocating an mm context.

No objection. Might have been better calling the low level guys
something like __get_mmu_context_id() / __put_mmu_context_id() but
we can rename later.

> Signed-off-by: Alexander Graf <agraf@suse.de>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

> ---
>  arch/powerpc/include/asm/mmu_context.h |    5 +++++
>  arch/powerpc/mm/mmu_context_hash64.c   |   24 +++++++++++++++++++++---
>  2 files changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> index b34e94d..66b35d0 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -23,6 +23,11 @@ extern void switch_slb(struct task_struct *tsk, struct mm_struct *mm);
>  extern void set_context(unsigned long id, pgd_t *pgd);
>  
>  #ifdef CONFIG_PPC_BOOK3S_64
> +extern int __init_new_context(void);
> +extern void __destroy_context(int context_id);
> +#endif
> +
> +#ifdef CONFIG_PPC_BOOK3S_64
>  static inline void mmu_context_init(void) { }
>  #else
>  extern void mmu_context_init(void);
> diff --git a/arch/powerpc/mm/mmu_context_hash64.c b/arch/powerpc/mm/mmu_context_hash64.c
> index dbeb86a..b9e4cc2 100644
> --- a/arch/powerpc/mm/mmu_context_hash64.c
> +++ b/arch/powerpc/mm/mmu_context_hash64.c
> @@ -18,6 +18,7 @@
>  #include <linux/mm.h>
>  #include <linux/spinlock.h>
>  #include <linux/idr.h>
> +#include <linux/module.h>
>  
>  #include <asm/mmu_context.h>
>  
> @@ -32,7 +33,7 @@ static DEFINE_IDR(mmu_context_idr);
>  #define NO_CONTEXT	0
>  #define MAX_CONTEXT	((1UL << 19) - 1)
>  
> -int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
> +int __init_new_context(void)
>  {
>  	int index;
>  	int err;
> @@ -57,6 +58,18 @@ again:
>  		return -ENOMEM;
>  	}
>  
> +	return index;
> +}
> +EXPORT_SYMBOL_GPL(__init_new_context);
> +
> +int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
> +{
> +	int index;
> +
> +	index = __init_new_context();
> +	if (index < 0)
> +		return index;
> +
>  	/* The old code would re-promote on fork, we don't do that
>  	 * when using slices as it could cause problem promoting slices
>  	 * that have been forced down to 4K
> @@ -68,11 +81,16 @@ again:
>  	return 0;
>  }
>  
> -void destroy_context(struct mm_struct *mm)
> +void __destroy_context(int context_id)
>  {
>  	spin_lock(&mmu_context_lock);
> -	idr_remove(&mmu_context_idr, mm->context.id);
> +	idr_remove(&mmu_context_idr, context_id);
>  	spin_unlock(&mmu_context_lock);
> +}
> +EXPORT_SYMBOL_GPL(__destroy_context);
>  
> +void destroy_context(struct mm_struct *mm)
> +{
> +	__destroy_context(mm->context.id);
>  	mm->context.id = NO_CONTEXT;
>  }