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authorShaohua Li <shli@fb.com>2017-04-26 09:18:35 -0700
committerJoerg Roedel <jroedel@suse.de>2017-04-26 23:57:53 +0200
commitbfd20f1cc85010d2f2d77e544da05cd8c149ba9b (patch)
tree1da8f1e85622fbf83264b356e1a840c0639b9b65 /arch/x86
parent161b28aae1651aa7ad63ec14753aa8a751154340 (diff)
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x86, iommu/vt-d: Add an option to disable Intel IOMMU force on
IOMMU harms performance signficantly when we run very fast networking workloads. It's 40GB networking doing XDP test. Software overhead is almost unaware, but it's the IOTLB miss (based on our analysis) which kills the performance. We observed the same performance issue even with software passthrough (identity mapping), only the hardware passthrough survives. The pps with iommu (with software passthrough) is only about ~30% of that without it. This is a limitation in hardware based on our observation, so we'd like to disable the IOMMU force on, but we do want to use TBOOT and we can sacrifice the DMA security bought by IOMMU. I must admit I know nothing about TBOOT, but TBOOT guys (cc-ed) think not eabling IOMMU is totally ok. So introduce a new boot option to disable the force on. It's kind of silly we need to run into intel_iommu_init even without force on, but we need to disable TBOOT PMR registers. For system without the boot option, nothing is changed. Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Joerg Roedel <jroedel@suse.de>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kernel/tboot.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
index b868fa1b812b..edbdfe6ab60a 100644
--- a/arch/x86/kernel/tboot.c
+++ b/arch/x86/kernel/tboot.c
@@ -510,6 +510,9 @@ int tboot_force_iommu(void)
if (!tboot_enabled())
return 0;
+ if (!intel_iommu_tboot_noforce)
+ return 1;
+
if (no_iommu || swiotlb || dmar_disabled)
pr_warning("Forcing Intel-IOMMU to enabled\n");