linux-kernel - [PATCH] Revert "dma-contiguous: check for memory region overlap"

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Message-ID: <1694073836-5125-1-git-send-email-quic_zhenhuah@quicinc.com>
Date:   Thu, 7 Sep 2023 16:03:56 +0800
From:   Zhenhua Huang <quic_zhenhuah@...cinc.com>
To:     <hch@....de>, <m.szyprowski@...sung.com>, <robin.murphy@....com>
CC:     Zhenhua Huang <quic_zhenhuah@...cinc.com>, <iommu@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, <quic_pkondeti@...cinc.com>,
        <quic_tingweiz@...cinc.com>
Subject: [PATCH] Revert "dma-contiguous: check for memory region overlap"

This reverts commit 3fa6456ebe13adab3ba1817c8e515a5b88f95dce.

The Commit broke the CMA region creation through DT on arm64,
as showed below logs with "memblock=debug":
[    0.000000] memblock_phys_alloc_range: 41943040 bytes align=0x200000
from=0x0000000000000000 max_addr=0x00000000ffffffff
early_init_dt_alloc_reserved_memory_arch+0x34/0xa0
[    0.000000] memblock_reserve: [0x00000000fd600000-0x00000000ffdfffff]
memblock_alloc_range_nid+0xc0/0x19c
[    0.000000] Reserved memory: overlap with other memblock reserved region

>From call flow, region we defined in DT was always reserved before entering
into rmem_cma_setup. Also, rmem_cma_setup has one routine cma_init_reserved_mem
to ensure the region was reserved. Checking the region not reserved here seems
not correct.

early_init_fdt_scan_reserved_mem:
    fdt_scan_reserved_mem
        __reserved_mem_reserve_reg
		early_init_dt_reserve_memory
			memblock_reserve(using “reg” prop case)
        fdt_init_reserved_mem
		__reserved_mem_alloc_size
			*early_init_dt_alloc_reserved_memory_arch*
				memblock_reserve(dynamic alloc case)
        __reserved_mem_init_node
		rmem_cma_setup(region overlap check here should always fail)

Example DT can be used to reproduce issue:

    dump_mem: mem_dump_region {
            compatible = "shared-dma-pool";
            alloc-ranges = <0x0 0x00000000 0x0 0xffffffff>;
            reusable;
            size = <0 0x2800000>;
    };

Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
---
 kernel/dma/contiguous.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 88c595e..f005c66 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -473,11 +473,6 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
 		return -EBUSY;
 	}
 
-	if (memblock_is_region_reserved(rmem->base, rmem->size)) {
-		pr_info("Reserved memory: overlap with other memblock reserved region\n");
-		return -EBUSY;
-	}
-
 	if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
 	    of_get_flat_dt_prop(node, "no-map", NULL))
 		return -EINVAL;
-- 
2.7.4