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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>
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@ -1578,6 +1578,15 @@
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extended tables themselves, and also PASID support. With
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this option set, extended tables will not be used even
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on hardware which claims to support them.
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tboot_noforce [Default Off]
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Do not force the Intel IOMMU enabled under tboot.
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By default, tboot will force Intel IOMMU on, which
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could harm performance of some high-throughput
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devices like 40GBit network cards, even if identity
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mapping is enabled.
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Note that using this option lowers the security
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provided by tboot because it makes the system
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vulnerable to DMA attacks.
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intel_idle.max_cstate= [KNL,HW,ACPI,X86]
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0 disables intel_idle and fall back on acpi_idle.
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@ -510,6 +510,9 @@ int tboot_force_iommu(void)
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if (!tboot_enabled())
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return 0;
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if (!intel_iommu_tboot_noforce)
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return 1;
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if (no_iommu || swiotlb || dmar_disabled)
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pr_warning("Forcing Intel-IOMMU to enabled\n");
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@ -183,6 +183,7 @@ static int rwbf_quirk;
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* (used when kernel is launched w/ TXT)
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*/
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static int force_on = 0;
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int intel_iommu_tboot_noforce;
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/*
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* 0: Present
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@ -607,6 +608,10 @@ static int __init intel_iommu_setup(char *str)
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"Intel-IOMMU: enable pre-production PASID support\n");
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intel_iommu_pasid28 = 1;
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iommu_identity_mapping |= IDENTMAP_GFX;
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} else if (!strncmp(str, "tboot_noforce", 13)) {
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printk(KERN_INFO
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"Intel-IOMMU: not forcing on after tboot. This could expose security risk for tboot\n");
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intel_iommu_tboot_noforce = 1;
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}
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str += strcspn(str, ",");
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@ -4850,6 +4855,19 @@ int __init intel_iommu_init(void)
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}
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if (no_iommu || dmar_disabled) {
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/*
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* We exit the function here to ensure IOMMU's remapping and
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* mempool aren't setup, which means that the IOMMU's PMRs
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* won't be disabled via the call to init_dmars(). So disable
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* it explicitly here. The PMRs were setup by tboot prior to
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* calling SENTER, but the kernel is expected to reset/tear
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* down the PMRs.
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*/
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if (intel_iommu_tboot_noforce) {
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for_each_iommu(iommu, drhd)
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iommu_disable_protect_mem_regions(iommu);
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}
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/*
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* Make sure the IOMMUs are switched off, even when we
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* boot into a kexec kernel and the previous kernel left
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@ -39,6 +39,7 @@ extern int iommu_calculate_agaw(struct intel_iommu *iommu);
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extern int iommu_calculate_max_sagaw(struct intel_iommu *iommu);
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extern int dmar_disabled;
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extern int intel_iommu_enabled;
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extern int intel_iommu_tboot_noforce;
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#else
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static inline int iommu_calculate_agaw(struct intel_iommu *iommu)
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{
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