Re: [PATCH v10 0/10] iommu/vt-d: Fix intel vt-d faults in kdump kernel

[Dave Young]

On 04/10/15 at 04:42pm, Li, Zhen-Hua wrote:
> This patchset is an update of Bill Sumner's patchset, implements a fix for:
> If a kernel boots with intel_iommu=on on a system that supports intel vt-d, 
> when a panic happens, the kdump kernel will boot with these faults:
> 
>     dmar: DRHD: handling fault status reg 102
>     dmar: DMAR:[DMA Read] Request device [01:00.0] fault addr fff80000
>     DMAR:[fault reason 01] Present bit in root entry is clear
> 
>     dmar: DRHD: handling fault status reg 2
>     dmar: INTR-REMAP: Request device [[61:00.0] fault index 42
>     INTR-REMAP:[fault reason 34] Present field in the IRTE entry is clear
> 
> On some system, the interrupt remapping fault will also happen even if the 
> intel_iommu is not set to on, because the interrupt remapping will be enabled 
> when x2apic is needed by the system.
> 
> The cause of the DMA fault is described in Bill's original version, and the 
> INTR-Remap fault is caused by a similar reason. In short, the initialization 
> of vt-d drivers causes the in-flight DMA and interrupt requests get wrong 
> response.
> 
> To fix this problem, we modifies the behaviors of the intel vt-d in the 
> crashdump kernel:
> 
> For DMA Remapping:
> 1. To accept the vt-d hardware in an active state,
> 2. Do not disable and re-enable the translation, keep it enabled.
> 3. Use the old root entry table, do not rewrite the RTA register.
> 4. Malloc and use new context entry table, copy data from the old ones that
>    used by the old kernel.
> 5. Keep using the old page tables before driver is loaded.
> 6. After device driver is loaded, when it issues the first dma_map command, 
>    free the dmar_domain structure for this device, and generate a new one, so 
>    that the device can be assigned a new and empty page table. 
> 7. When a new context entry table is generated, we also save its address to 
>    the old root entry table.
> 
> For Interrupt Remapping:
> 1. To accept the vt-d hardware in an active state,
> 2. Do not disable and re-enable the interrupt remapping, keep it enabled.
> 3. Use the old interrupt remapping table, do not rewrite the IRTA register.
> 4. When ioapic entry is setup, the interrupt remapping table is changed, and 
>    the updated data will be stored to the old interrupt remapping table.
> 
> Advantages of this approach:
> 1. All manipulation of the IO-device is done by the Linux device-driver
>    for that device.
> 2. This approach behaves in a manner very similar to operation without an
>    active iommu.
> 3. Any activity between the IO-device and its RMRR areas is handled by the
>    device-driver in the same manner as during a non-kdump boot.
> 4. If an IO-device has no driver in the kdump kernel, it is simply left alone.
>    This supports the practice of creating a special kdump kernel without
>    drivers for any devices that are not required for taking a crashdump. 
> 5. Minimal code-changes among the existing mainline intel vt-d code.
> 
> Summary of changes in this patch set:
> 1. Added some useful function for root entry table in code intel-iommu.c
> 2. Added new members to struct root_entry and struct irte;
> 3. Functions to load old root entry table to iommu->root_entry from the memory 
>    of old kernel.
> 4. Functions to malloc new context entry table and copy the data from the old
>    ones to the malloced new ones.
> 5. Functions to enable support for DMA remapping in kdump kernel.
> 6. Functions to load old irte data from the old kernel to the kdump kernel.
> 7. Some code changes that support other behaviours that have been listed.
> 8. In the new functions, use physical address as "unsigned long" type, not 
>    pointers.
> 
> Original version by Bill Sumner:
>     https://lkml.org/lkml/2014/1/10/518
>     https://lkml.org/lkml/2014/4/15/716
>     https://lkml.org/lkml/2014/4/24/836
> 
> Zhenhua's updates:
>     https://lkml.org/lkml/2014/10/21/134
>     https://lkml.org/lkml/2014/12/15/121
>     https://lkml.org/lkml/2014/12/22/53
>     https://lkml.org/lkml/2015/1/6/1166
>     https://lkml.org/lkml/2015/1/12/35
>     https://lkml.org/lkml/2015/3/19/33
> 
> Changelog[v10]:
>     1. Do not use CONFIG_CRASH_DUMP and is_kdump_kernel().
>        Use one flag which stores the te and ir status in last kernel:
>            iommu->pre_enabled_trans
>            iommu->pre_enabled_ir
> 
> Changelog[v9]:
>     1. Add new function iommu_attach_domain_with_id.
>     2. Do not copy old page tables, keep using the old ones.
>     3. Remove functions:
>            intel_iommu_did_to_domain_values_entry
>            intel_iommu_get_dids_from_old_kernel
>            device_to_domain_id
>            copy_page_addr
>            copy_page_table
>            copy_context_entry
>            copy_context_entry_table
>     4. Add new function device_to_existing_context_entry.
> 
> Changelog[v8]:
>     1. Add a missing __iommu_flush_cache in function copy_page_table.
> 
> Changelog[v7]:
>     1. Use __iommu_flush_cache to flush the data to hardware.
> 
> Changelog[v6]:
>     1. Use "unsigned long" as type of physical address.
>     2. Use new function unmap_device_dma to unmap the old dma.
>     3. Some small incorrect bits order for aw shift.
> 
> Changelog[v5]:
>     1. Do not disable and re-enable traslation and interrupt remapping. 
>     2. Use old root entry table.
>     3. Use old interrupt remapping table.
>     4. New functions to copy data from old kernel, and save to old kernel mem.
>     5. New functions to save updated root entry table and irte table.
>     6. Use intel_unmap to unmap the old dma;
>     7. Allocate new pages while driver is being loaded.
> 
> Changelog[v4]:
>     1. Cut off the patches that move some defines and functions to new files.
>     2. Reduce the numbers of patches to five, make it more easier to read.
>     3. Changed the name of functions, make them consistent with current context
>        get/set functions.
>     4. Add change to function __iommu_attach_domain.
> 
> Changelog[v3]:
>     1. Commented-out "#define DEBUG 1" to eliminate debug messages.
>     2. Updated the comments about changes in each version.
>     3. Fixed: one-line added to Copy-Translations patch to initialize the iovad
>           struct as recommended by Baoquan He [bhe@xxxxxxxxxx]
>           init_iova_domain(&domain->iovad, DMA_32BIT_PFN);
> 
> Changelog[v2]:
>     The following series implements a fix for:
>     A kdump problem about DMA that has been discussed for a long time. That is,
>     when a kernel panics and boots into the kdump kernel, DMA started by the
>     panicked kernel is not stopped before the kdump kernel is booted and the
>     kdump kernel disables the IOMMU while this DMA continues.  This causes the
>     IOMMU to stop translating the DMA addresses as IOVAs and begin to treat
>     them as physical memory addresses -- which causes the DMA to either:
>         (1) generate DMAR errors or 
>         (2) generate PCI SERR errors or 
>         (3) transfer data to or from incorrect areas of memory. Often this 
>             causes the dump to fail.
> 
> Changelog[v1]:
>     The original version.
> 
> Changed in this version:
> 1. Do not disable and re-enable traslation and interrupt remapping. 
> 2. Use old root entry table.
> 3. Use old interrupt remapping table.
> 4. Use "unsigned long" as physical address.
> 5. Use intel_unmap to unmap the old dma;
> 
> Baoquan He <bhe@xxxxxxxxxx> helps testing this patchset.
> Takao Indoh <indou.takao@xxxxxxxxxxxxxx> gives valuable suggestions.
> 
> Li, Zhen-Hua (10):
>   iommu/vt-d: New function to attach domain with id
>   iommu/vt-d: Items required for kdump
>   iommu/vt-d: Function to get old context entry
>   iommu/vt-d: functions to copy data from old mem
>   iommu/vt-d: Add functions to load and save old re
>   iommu/vt-d: datatypes and functions used for kdump
>   iommu/vt-d: enable kdump support in iommu module
>   iommu/vt-d: assign new page table for dma_map
>   iommu/vt-d: Copy functions for irte
>   iommu/vt-d: Use old irte in kdump kernel
> 
>  drivers/iommu/intel-iommu.c         | 518 ++++++++++++++++++++++++++++++++++--
>  drivers/iommu/intel_irq_remapping.c |  96 ++++++-
>  include/linux/intel-iommu.h         |  16 ++
>  3 files changed, 605 insertions(+), 25 deletions(-)
> 
> -- 
> 2.0.0-rc0


Again, I think it is bad to use old page table, below issues need consider:
1) make sure old page table are reliable across crash
2) do not allow writing oldmem after crash

Please correct me if I'm wrong, or if above is not doable I think I will vote for
resetting pci bus.

Thanks
Dave
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