[OpenBIOS] [PATCH] ppc: fix reuse of MMU translation slots

[Mark Cave-Ayland]

On 10/02/16 23:25, Alyssa Milburn wrote:

> The current code always picks slot 0 in the reuse case. (This doesn't seem
> to matter in the cases I've tested, though.)
> 
> Signed-off-by: Alyssa Milburn <fuzzie at fuzzie.org>
> ---
>  arch/ppc/qemu/ofmem.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/ppc/qemu/ofmem.c b/arch/ppc/qemu/ofmem.c
> index 6f346a3..c9fe154 100644
> --- a/arch/ppc/qemu/ofmem.c
> +++ b/arch/ppc/qemu/ofmem.c
> @@ -359,9 +359,11 @@ hash_page_64(unsigned long ea, phys_addr_t phys, ucell mode)
>              found = 1;
>  
>      /* otherwise use a free slot */
> -    for (i = 0; !found && i < 8; i++)
> -        if (!pp[i].v)
> -            found = 1;
> +    if (!found) {
> +        for (i = 0; !found && i < 8; i++)
> +            if (!pp[i].v)
> +                found = 1;
> +    }
>  
>      /* out of slots, just evict one */
>      if (!found)
> @@ -414,9 +416,11 @@ hash_page_32(unsigned long ea, phys_addr_t phys, ucell mode)
>              found = 1;
>  
>      /* otherwise use a free slot */
> -    for (i = 0; !found && i < 8; i++)
> -        if (!pp[i].v)
> -            found = 1;
> +    if (!found) {
> +        for (i = 0; !found && i < 8; i++)
> +            if (!pp[i].v)
> +                found = 1;
> +    }
>  
>      /* out of slots, just evict one */
>      if (!found)
> 

Hmmm yes I think you're right there is a bug here. Assuming that we
locate the index of an old translation, then i should be set to the slot
number to replace. But even though found has been set, the subsequent
for() will always reset i to zero, even though it exits without iterating.

In theory this could mean that we have multiple entries in the hash
table for the same translation which can't be a good thing.

Alex - does this look like the right solution to you?


ATB,

Mark.