[2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault()

Submitted by Christophe Leroy on April 19, 2017, 12:56 p.m.

Details

Message ID 58f17a04cee5726467ef4e283dfbd7da68fa6ab4.1492606298.git.christophe.leroy@c-s.fr
State New
Headers show

Commit Message

Christophe Leroy April 19, 2017, 12:56 p.m.
Only the get_user() in store_updates_sp() has to be done outside
the mm semaphore. All the comparison can be done within the semaphore,
so only when really needed.

As we got a DSI exception, the address pointed by regs->nip is
obviously valid, otherwise we would have had a instruction exception.
So __get_user() can be used instead of get_user()

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/mm/fault.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

Comments

Aneesh Kumar K.V April 24, 2017, 9:11 a.m.
Christophe Leroy <christophe.leroy@c-s.fr> writes:

> Only the get_user() in store_updates_sp() has to be done outside
> the mm semaphore. All the comparison can be done within the semaphore,
> so only when really needed.
>
> As we got a DSI exception, the address pointed by regs->nip is
> obviously valid, otherwise we would have had a instruction exception.
> So __get_user() can be used instead of get_user()
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/mm/fault.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 67fefb59d40e..9d21e5fd383d 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -73,12 +73,8 @@ static inline int notify_page_fault(struct pt_regs *regs)
>   * Check whether the instruction at regs->nip is a store using
>   * an update addressing form which will update r1.
>   */
> -static int store_updates_sp(struct pt_regs *regs)
> +static int store_updates_sp(unsigned int inst)
>  {
> -	unsigned int inst;
> -
> -	if (get_user(inst, (unsigned int __user *)regs->nip))
> -		return 0;
>  	/* check for 1 in the rA field */
>  	if (((inst >> 16) & 0x1f) != 1)
>  		return 0;
> @@ -207,7 +203,8 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  	int trap = TRAP(regs);
>   	int is_exec = trap == 0x400;
>  	int fault;
> -	int rc = 0, store_update_sp = 0;
> +	int rc = 0;
> +	unsigned int inst = 0;
>  
>  #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
>  	/*
> @@ -288,7 +285,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  	 * mmap_sem held
>  	 */
>  	if (is_write && user_mode(regs))
> -		store_update_sp = store_updates_sp(regs);
> +		__get_user(inst, (unsigned int __user *)regs->nip);
>  
>  	if (user_mode(regs))
>  		flags |= FAULT_FLAG_USER;
> @@ -358,7 +355,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  		 * between the last mapped region and the stack will
>  		 * expand the stack rather than segfaulting.
>  		 */
> -		if (address + 2048 < uregs->gpr[1] && !store_update_sp)
> +		if (address + 2048 < uregs->gpr[1] && !store_updates_sp(inst))
>  			goto bad_area;
>  	}
>  	if (expand_stack(vma, address))
> -- 
> 2.12.0

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diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 67fefb59d40e..9d21e5fd383d 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -73,12 +73,8 @@  static inline int notify_page_fault(struct pt_regs *regs)
  * Check whether the instruction at regs->nip is a store using
  * an update addressing form which will update r1.
  */
-static int store_updates_sp(struct pt_regs *regs)
+static int store_updates_sp(unsigned int inst)
 {
-	unsigned int inst;
-
-	if (get_user(inst, (unsigned int __user *)regs->nip))
-		return 0;
 	/* check for 1 in the rA field */
 	if (((inst >> 16) & 0x1f) != 1)
 		return 0;
@@ -207,7 +203,8 @@  int do_page_fault(struct pt_regs *regs, unsigned long address,
 	int trap = TRAP(regs);
  	int is_exec = trap == 0x400;
 	int fault;
-	int rc = 0, store_update_sp = 0;
+	int rc = 0;
+	unsigned int inst = 0;
 
 #if !(defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
 	/*
@@ -288,7 +285,7 @@  int do_page_fault(struct pt_regs *regs, unsigned long address,
 	 * mmap_sem held
 	 */
 	if (is_write && user_mode(regs))
-		store_update_sp = store_updates_sp(regs);
+		__get_user(inst, (unsigned int __user *)regs->nip);
 
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
@@ -358,7 +355,7 @@  int do_page_fault(struct pt_regs *regs, unsigned long address,
 		 * between the last mapped region and the stack will
 		 * expand the stack rather than segfaulting.
 		 */
-		if (address + 2048 < uregs->gpr[1] && !store_update_sp)
+		if (address + 2048 < uregs->gpr[1] && !store_updates_sp(inst))
 			goto bad_area;
 	}
 	if (expand_stack(vma, address))