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authorBernhard Walle <bwalle@suse.de>2008-05-14 15:40:40 -0700
committerTony Luck <tony.luck@intel.com>2008-05-14 15:40:40 -0700
commit8a3360f06cd4d3b1d57f73e029f2f8b6057fdcba (patch)
tree299eee7ef2848e29cec8894fd9e13c7151771c21 /Documentation
parent2224661494278bfc1c35b392cf6ee6f58e1d5e64 (diff)
[IA64] Don't reserve crashkernel memory > 4 GB
Some IA64 machines map all cell-local memory above 4 GB (32 bit limit). However, in most cases, the kernel needs some memory below that limit that is DMA-capable. So in this machine configuration, the crashkernel will be reserved above 4 GB. For machines that use SWIOTLB implementation because they lack an I/O MMU the low memory is required by the SWIOTLB implementation. In that case, it doesn't make sense to reserve the crashkernel at all because it's unusable for kdump. A special case is the "hpzx1" machine vector. In theory, it has a I/O MMU, so it can be booted above 4 GB. However, in the kdump case that is not possible because of changeset 51b58e3e26ebfb8cd56825c4b396ed251f51dec9: On HP zx1 machines, the 'machvec=dig' parameter is needed for the kdump kernel to avoid problems with the HP sba iommu. The problem is that during the boot of the kdump kernel, the iommu is re-initialized, so in-flight DMA from improperly shutdown drivers causes an IOTLB miss which leads to an MCA. With kdump, the idea is to get into the kdump kernel with as little code as we can, so shutting down drivers properly is not an option. The workaround is to add 'machvec=dig' to the kdump kernel boot parameters. This makes the kdump kernel avoid using the sba iommu altogether, leaving the IOTLB intact. Any ongoing DMA falls harmlessly outside the kdump kernel. After the kdump kernel reboots, all devices will have been shutdown properly and DMA stopped. This patch pushes that functionality into the sba iommu initialization code, so that users won't have to find the obscure documentation telling them about 'machvec=dig'. This means that also for hpzx1 it's not possible to boot when all memory is above the 4 GB limit. So the only machine vectors that can handle this case are "sn2" and "uv". Signed-off-by: Bernhard Walle <bwalle@suse.de> Signed-off-by: Tony Luck <tony.luck@intel.com>
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