[PATCH] MIPS: c-r4k: Fix size calc when avoiding IPIs for small icache flushes

[PATCH] MIPS: c-r4k: Fix size calc when avoiding IPIs for small icache flushes

[Paul Burton]

Commit f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP
calls") adds checks to force use of hit-type cache ops for small icache
flushes where they are globalised & index-type cache ops aren't, in
order to avoid the overhead of IPIs in those cases. However it
calculated the size of the region being flushed incorrectly, subtracting
the end address from the start address rather than the reverse. This
would have led to an overflow with size wrapping round to some large
value, and likely to the special case for avoiding IPIs not actually
being hit.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Fixes: f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP calls")
---

 arch/mips/mm/c-r4k.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index 1af381f..69b1f10 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -811,7 +811,7 @@ static void __r4k_flush_icache_range(unsigned long start, unsigned long end,
 		 * If address-based cache ops don't require an SMP call, then
 		 * use them exclusively for small flushes.
 		 */
-		size = start - end;
+		size = end - start;
 		cache_size = icache_size;
 		if (!cpu_has_ic_fills_f_dc) {
 			size *= 2;
-- 
2.9.3

Re: [PATCH] MIPS: c-r4k: Fix size calc when avoiding IPIs for small icache flushes

[James Hogan]

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On Mon, Sep 05, 2016 at 03:24:54PM +0100, Paul Burton wrote:
> Commit f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP
> calls") adds checks to force use of hit-type cache ops for small icache
> flushes where they are globalised & index-type cache ops aren't, in
> order to avoid the overhead of IPIs in those cases. However it
> calculated the size of the region being flushed incorrectly, subtracting
> the end address from the start address rather than the reverse. This
> would have led to an overflow with size wrapping round to some large
> value, and likely to the special case for avoiding IPIs not actually
> being hit.
> 
> Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> Cc: James Hogan <james.hogan@imgtec.com>
> Fixes: f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP calls")

Good catch Paul! I've no idea how that happened.

Reviewed-by: James Hogan <james.hogan@imgtec.com>

Ralf: It'd be great to get this into v4.8 if possible.

Thanks
James

> ---
> 
>  arch/mips/mm/c-r4k.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
> index 1af381f..69b1f10 100644
> --- a/arch/mips/mm/c-r4k.c
> +++ b/arch/mips/mm/c-r4k.c
> @@ -811,7 +811,7 @@ static void __r4k_flush_icache_range(unsigned long start, unsigned long end,
>  		 * If address-based cache ops don't require an SMP call, then
>  		 * use them exclusively for small flushes.
>  		 */
> -		size = start - end;
> +		size = end - start;
>  		cache_size = icache_size;
>  		if (!cpu_has_ic_fills_f_dc) {
>  			size *= 2;
> -- 
> 2.9.3
> 

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Re: [PATCH] MIPS: c-r4k: Fix size calc when avoiding IPIs for small icache flushes

[Florian Fainelli]

On 09/05/2016 07:24 AM, Paul Burton wrote:
> Commit f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP
> calls") adds checks to force use of hit-type cache ops for small icache
> flushes where they are globalised & index-type cache ops aren't, in
> order to avoid the overhead of IPIs in those cases. However it
> calculated the size of the region being flushed incorrectly, subtracting
> the end address from the start address rather than the reverse. This
> would have led to an overflow with size wrapping round to some large
> value, and likely to the special case for avoiding IPIs not actually
> being hit.
> 
> Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> Cc: James Hogan <james.hogan@imgtec.com>
> Fixes: f70ddc07b637 ("MIPS: c-r4k: Avoid small flush_icache_range SMP calls")

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>

Yes would be good to get that in v4.8.
-- 
Florian