Subject: Re: [PATCH kernel 1/2] powerpc/powernv: Fix insufficient memory allocation

From: Gavin Shan <[email-masked]>
Date: Thu, 12 May 2016 16:09:25 +1000

On Thu, May 12, 2016 at 03:47:09PM +1000, Alexey Kardashevskiy wrote:
>The pnv_pci_init_ioda_phb() helper allocates a blob to store auxilary
>data such PE and M32/M64 segment allocation maps; this single blob has few
>partitions, size of each is derived from the PE number -
>phb->ioda.total_pe_num.
>
>It was assumed that the minimum PE number is 8, however it is 4 for NPU
>so the pe_alloc part was missing in the allocated blob.
>It was invisible till recently as we were not tracking used M64 segments
>and NPUs do not use M32 segments so the phb->ioda.m32_segmap
>(which was pointing to the same address as phb->ioda.pe_alloc)
>has never been written to leaving the pe_alloc memory intact.
>
>After 401203ac2d "powerpc/powernv: Track M64 segment consumption"
>the pe_alloc gets corrupted and PE allocation cannot work.
>This fixes the issue by enforcing the minimum PE number to 8.
>

As I said offline yesterday, the issue exists from day-1 when NPU PHB
is supported. I don't think it's related to 401203ac2d. Without the logic
tracking M64 segments, the PE# bitmap still can be corrupted when writting
to M32 segment map. It's confusing to mention a unrelated commit in the
changelog.

Since the issue exists from day-1 when NPU PHB is supported, is a stable
tag needed?

>Signed-off-by: Alexey Kardashevskiy <[email-masked]>

With above parts fixed:

Reviewed-by: Gavin Shan <[email-masked]>

>---
> arch/powerpc/platforms/powernv/pci-ioda.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>index 6cda2a8..d0d32c2 100644
>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>@@ -3507,7 +3507,8 @@ static void __init pnv_pci_init_ioda_phb(struct device_node *np,
> 				PNV_IODA1_DMA32_SEGSIZE;
>
> 	/* Allocate aux data & arrays. We don't have IO ports on PHB3 */
>-	size = _ALIGN_UP(phb->ioda.total_pe_num / 8, sizeof(unsigned long));
>+	size = _ALIGN_UP(max_t(unsigned, phb->ioda.total_pe_num, 8) / 8,
>+			sizeof(unsigned long));
> 	m64map_off = size;
> 	size += phb->ioda.total_pe_num * sizeof(phb->ioda.m64_segmap[0]);
> 	m32map_off = size;
>-- 
>2.5.0.rc3
>