Michael Ellerman <m...@ellerman.id.au> writes:
> The recent rewrite of the SLB code into C included the assumption that
> all CPUs we run on have at least 32 SLB entries. This is currently
> true but a bit fragile as the SLB size is actually defined by the
> device tree and so could theoretically change at any time.
>
> The assumption is encoded in the fact that we use U32_MAX as the value
> for a full SLB bitmap. Instead, calculate what the full bitmap would
> be based on the SLB size we're given and store it. This still requires
> the SLB size to be a power of 2.
So if it is less than 32 we want to make sure we don't allocate an index
above 32. Is this the reason for that radom assert_slb_presence?
Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
>
> Fixes: 126b11b294d1 ("powerpc/64s/hash: Add SLB allocation status bitmaps")
> Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
> ---
> arch/powerpc/mm/slb.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
> index bc3914d54e26..61450a9cf30d 100644
> --- a/arch/powerpc/mm/slb.c
> +++ b/arch/powerpc/mm/slb.c
> @@ -506,9 +506,16 @@ void switch_slb(struct task_struct *tsk, struct
> mm_struct *mm)
> asm volatile("isync" : : : "memory");
> }
>
> +static u32 slb_full_bitmap;
> +
> void slb_set_size(u16 size)
> {
> mmu_slb_size = size;
> +
> + if (size >= 32)
> + slb_full_bitmap = U32_MAX;
> + else
> + slb_full_bitmap = (1ul << size) - 1;
> }
>
> void slb_initialize(void)
> @@ -611,7 +618,7 @@ static enum slb_index alloc_slb_index(bool kernel)
> * POWER7/8/9 have 32 SLB entries, this could be expanded if a
> * future CPU has more.
> */
> - if (local_paca->slb_used_bitmap != U32_MAX) {
> + if (local_paca->slb_used_bitmap != slb_full_bitmap) {
> index = ffz(local_paca->slb_used_bitmap);
> local_paca->slb_used_bitmap |= 1U << index;
> if (kernel)
> --
> 2.20.1
