linux-kernel - [PATCH] arm64: mm: fix zone_dma

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Message-ID: <20241125171650.77424-1-yang@os.amperecomputing.com>
Date: Mon, 25 Nov 2024 09:16:50 -0800
From: Yang Shi <yang@...amperecomputing.com>
To: catalin.marinas@....com,
	will@...nel.org,
	baruch@...s.co.il,
	ptesarik@...e.com,
	hch@....de
Cc: yang@...amperecomputing.com,
	jiangyutang@...amperecomputing.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: mm: fix zone_dma_limit calculation

The commit ba0fb44aed47 ("dma-mapping: replace zone_dma_bits by
zone_dma_limit") changed how zone_dma_limit was calculated.  Now it
returns the memsize limit in IORT or device tree instead of U32_MAX if
the memsize limit is greater than U32_MAX.

This resulted in DMA allocations may use GFP_DMA even though the devices
don't require it.  It caused regression on our two sockets systems due
to excessive remote memory access.

Fixes: ba0fb44aed47 ("dma-mapping: replace zone_dma_bits by zone_dma_limit")
Cc: <stable@...r.kernel.org>    [6.12+]
Reported-by: Yutang Jiang <jiangyutang@...amperecomputing.com>
Tested-by: Yutang Jiang <jiangyutang@...amperecomputing.com>
Signed-off-by: Yang Shi <yang@...amperecomputing.com>
---
 arch/arm64/mm/init.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index d21f67d67cf5..ccdef53872a0 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -117,15 +117,6 @@ static void __init arch_reserve_crashkernel(void)
 
 static phys_addr_t __init max_zone_phys(phys_addr_t zone_limit)
 {
-	/**
-	 * Information we get from firmware (e.g. DT dma-ranges) describe DMA
-	 * bus constraints. Devices using DMA might have their own limitations.
-	 * Some of them rely on DMA zone in low 32-bit memory. Keep low RAM
-	 * DMA zone on platforms that have RAM there.
-	 */
-	if (memblock_start_of_DRAM() < U32_MAX)
-		zone_limit = min(zone_limit, U32_MAX);
-
 	return min(zone_limit, memblock_end_of_DRAM() - 1) + 1;
 }
 
@@ -141,6 +132,14 @@ static void __init zone_sizes_init(void)
 	acpi_zone_dma_limit = acpi_iort_dma_get_max_cpu_address();
 	dt_zone_dma_limit = of_dma_get_max_cpu_address(NULL);
 	zone_dma_limit = min(dt_zone_dma_limit, acpi_zone_dma_limit);
+	/*
+	 * Information we get from firmware (e.g. DT dma-ranges) describe DMA
+	 * bus constraints. Devices using DMA might have their own limitations.
+	 * Some of them rely on DMA zone in low 32-bit memory. Keep low RAM
+	 * DMA zone on platforms that have RAM there.
+	 */
+	if (memblock_start_of_DRAM() < U32_MAX)
+		zone_dma_limit = min(zone_dma_limit, U32_MAX);
 	arm64_dma_phys_limit = max_zone_phys(zone_dma_limit);
 	max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit);
 #endif
-- 
2.47.0