netdev - [PATCH 2/2] swiotlb: Return consistent SWIOTLB segments/nr

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Date:   Tue, 11 Jun 2019 10:58:25 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     bcm-kernel-feedback-list@...adcom.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        iommu@...ts.linux-foundation.org (open list:DMA MAPPING HELPERS),
        netdev@...r.kernel.org (open list:NETWORKING [GENERAL])
Subject: [PATCH 2/2] swiotlb: Return consistent SWIOTLB segments/nr_tbl

With a specifically contrived memory layout where there is no physical
memory available to the kernel below the 4GB boundary, we will fail to
perform the initial swiotlb_init() call and set no_iotlb_memory to true.

There are drivers out there that call into swiotlb_nr_tbl() to determine
whether they can use the SWIOTLB. With the right DMA_BIT_MASK() value
for these drivers (say 64-bit), they won't ever need to hit
swiotlb_tbl_map_single() so this can go unoticed and we would be
possibly lying about those drivers.

Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
 kernel/dma/swiotlb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index b2b5c5df273c..e906ef2e6315 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -129,15 +129,17 @@ setup_io_tlb_npages(char *str)
 }
 early_param("swiotlb", setup_io_tlb_npages);
 
+static bool no_iotlb_memory;
+
 unsigned long swiotlb_nr_tbl(void)
 {
-	return io_tlb_nslabs;
+	return unlikely(no_iotlb_memory) ? 0 : io_tlb_nslabs;
 }
 EXPORT_SYMBOL_GPL(swiotlb_nr_tbl);
 
 unsigned int swiotlb_max_segment(void)
 {
-	return max_segment;
+	return unlikely(no_iotlb_memory) ? 0 : max_segment;
 }
 EXPORT_SYMBOL_GPL(swiotlb_max_segment);
 
@@ -160,8 +162,6 @@ unsigned long swiotlb_size_or_default(void)
 	return size ? size : (IO_TLB_DEFAULT_SIZE);
 }
 
-static bool no_iotlb_memory;
-
 void swiotlb_print_info(void)
 {
 	unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT;
-- 
2.17.1