From: Bhavna Sarathy <bnagendr@redhat.com>
Date: Mon, 27 Sep 2010 16:31:36 -0400
Subject: [misc] amd_iommu: fix kdump OOM issue seen with iommu=pt
Message-id: <20100927163138.16943.52724.sendpatchset@localhost.localdomain>
Patchwork-id: 28423
O-Subject: [RHEL5.6 PATCH] Fix kdump OOM issue seen with iommu=pt
Bugzilla: 627663
RH-Acked-by: Chris Wright <chrisw@redhat.com>
RH-Acked-by: Neil Horman <nhorman@redhat.com>

Resolves 627663

This patch fixes the kdump issue introduced by AMD passthrough mode patch.   It
checks the end_pfn and only sets swiotlb if the end_pfn > MAX_DMA32_PFN.  Note
that in RHEL6 this check was with max_pfn, but in RHEl5 it is end_pfn.
In the kdump kernel end_pfn seems to point to the end of the kdump memory which is
below 4gb and thus swiotlb is now 0 and the 64M are not longer allocated at boot
of the kdump kernel.

Fixes the OOM issues seen with kdump kernels.

Please note dependencies and apply patches in the following order:
1) IOMMU passthrough mode support
2) Change default to iommu=pt
3) kdump fix to iommu passthrough mode patch

Testing done successfully on Dinar system, the OOM kill was fixed with this patch.
[ PASS ] kdump works in IOMMU passthrough mode, SWIOTLB is turned off

    1. Installed kexec-tools
    2. Turned on the kdump init script (chkconfig kdump on)
    3. Booted the kernel with the parameter 'crashkernel=128M@16M'
    4. Did an 'echo c > /proc/sysrq-trigger'
    5. System booted into the crash kernel and saved the state
    6. No PCI-DMA messages from crash kernel (SWIOTLB is turned off)
    7. System rebooted itself
    8. Checked for the presence of a file in /var/crash

Please review and ACK.

Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/arch/x86_64/kernel/amd_iommu_init.c b/arch/x86_64/kernel/amd_iommu_init.c
index 9ddfa5d..6b827bc 100644
--- a/arch/x86_64/kernel/amd_iommu_init.c
+++ b/arch/x86_64/kernel/amd_iommu_init.c
@@ -27,6 +27,7 @@
 #include <asm/pci-direct.h>
 #include <asm/amd_iommu_types.h>
 #include <asm/amd_iommu.h>
+#include <asm/dma.h>
 
 /*
  * definitions for the ACPI scanning code
@@ -1206,7 +1207,7 @@ void __init amd_iommu_detect(void)
 		 */
 		iommu_pass_through = amd_iommu_force_nopt ? 0 : 1;
 	
-		if (iommu_pass_through)
+		if (iommu_pass_through && end_pfn > MAX_DMA32_PFN)
 			swiotlb = 1;
 	}
 }