linux-kernel - [PATCH] powerpc: ensure that swiotlb buffer is allocated from low memory

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Date:   Wed,  4 Dec 2019 14:35:24 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Christian Zigotzky <chzigotzky@...osoft.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Darren Stevens <darren@...vens-zone.net>,
        mad skateman <madskateman@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Paul Mackerras <paulus@...ba.org>,
        Robin Murphy <robin.murphy@....com>,
        Rob Herring <robh+dt@...nel.org>
Subject: [PATCH] powerpc: ensure that swiotlb buffer is allocated from low memory

From: Mike Rapoport <rppt@...ux.ibm.com>

Some powerpc platforms (e.g. 85xx) limit DMA-able memory way below 4G. If a
system has more physical memory than this limit, the swiotlb buffer is not
addressable because it is allocated from memblock using top-down mode.

Force memblock to bottom-up mode before calling swiotlb_init() to ensure
that the swiotlb buffer is DMA-able.

Link: https://lkml.kernel.org/r/F1EBB706-73DF-430E-9020-C214EC8ED5DA@xenosoft.de
Reported-by: Christian Zigotzky <chzigotzky@...osoft.de>
Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Darren Stevens <darren@...vens-zone.net>
Cc: mad skateman <madskateman@...il.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Robin Murphy <robin.murphy@....com>
Cc: Rob Herring <robh+dt@...nel.org>
---
 arch/powerpc/mm/mem.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index be941d382c8d..14c2c53e3f9e 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -260,6 +260,14 @@ void __init mem_init(void)
 	BUILD_BUG_ON(MMU_PAGE_COUNT > 16);
 
 #ifdef CONFIG_SWIOTLB
+	/*
+	 * Some platforms (e.g. 85xx) limit DMA-able memory way below
+	 * 4G. We force memblock to bottom-up mode to ensure that the
+	 * memory allocated in swiotlb_init() is DMA-able.
+	 * As it's the last memblock allocation, no need to reset it
+	 * back to to-down.
+	 */
+	memblock_set_bottom_up(true);
 	swiotlb_init(0);
 #endif
 
-- 
2.24.0