linux-kernel - [PATCH v7u1 26/31] x86: Don't enable swiotlb if there is not enough ram for it

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Date:	Thu,  3 Jan 2013 16:48:46 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>, Jan Kiszka <jan.kiszka@....de>,
	Jason Wessel <jason.wessel@...driver.com>,
	linux-kernel@...r.kernel.org, Yinghai Lu <yinghai@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Joerg Roedel <joro@...tes.org>
Subject: [PATCH v7u1 26/31] x86: Don't enable swiotlb if there is not enough ram for it

Normal boot path on system with iommu support:
swiotlb buffer will be allocated early at first and then try to initialize
iommu, if iommu for intel or amd could setup properly, swiotlb buffer
will be freed.

The early allocating is with bootmem, and get panic when we try to use
kdump with buffer above 4G only if swiotlb is enabled.

because actually the kernel can go on without swiotlb, and use intel iommu.

Try disable swiotlb if there is not enough ram for it.

That is for kdump to use kernel above 4G.

Suggested-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Yinghai Lu <yinghai@...nel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Joerg Roedel <joro@...tes.org>
---
 arch/x86/kernel/pci-swiotlb.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index 6c483ba..949ebfe 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -6,6 +6,7 @@
 #include <linux/swiotlb.h>
 #include <linux/bootmem.h>
 #include <linux/dma-mapping.h>
+#include <linux/memblock.h>
 
 #include <asm/iommu.h>
 #include <asm/swiotlb.h>
@@ -50,6 +51,11 @@ static struct dma_map_ops swiotlb_dma_ops = {
 	.dma_supported = NULL,
 };
 
+static bool __init enough_mem_for_swiotlb(void)
+{
+	/* do we have less than 1M RAM under 4G ? */
+	return memblock_mem_size(1ULL<<(32-PAGE_SHIFT)) > (1ULL<<20);
+}
 /*
  * pci_swiotlb_detect_override - set swiotlb to 1 if necessary
  *
@@ -58,12 +64,12 @@ static struct dma_map_ops swiotlb_dma_ops = {
  */
 int __init pci_swiotlb_detect_override(void)
 {
-	int use_swiotlb = swiotlb | swiotlb_force;
-
 	if (swiotlb_force)
 		swiotlb = 1;
+	else if (!enough_mem_for_swiotlb())
+		swiotlb = 0;
 
-	return use_swiotlb;
+	return swiotlb;
 }
 IOMMU_INIT_FINISH(pci_swiotlb_detect_override,
 		  pci_xen_swiotlb_detect,
@@ -78,7 +84,7 @@ int __init pci_swiotlb_detect_4gb(void)
 {
 	/* don't initialize swiotlb if iommu=off (no_iommu=1) */
 #ifdef CONFIG_X86_64
-	if (!no_iommu && max_pfn > MAX_DMA32_PFN)
+	if (!no_iommu && max_pfn > MAX_DMA32_PFN && enough_mem_for_swiotlb())
 		swiotlb = 1;
 #endif
 	return swiotlb;
-- 
1.7.10.4

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