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Commita166563e7e("arm64: mm: support large block mapping when rodata=full") enabled the linear map to be mapped by block/cont while still allowing granular permission changes on BBML2_NOABORT systems by lazily splitting the live mappings. This mechanism was intended to be usable by realm guests since they need to dynamically share dma buffers with the host by "decrypting" them - which for Arm CCA, means marking them as shared in the page tables. However, it turns out that the mechanism was failing for realm guests because realms need to share their dma buffers (via __set_memory_enc_dec()) much earlier during boot than split_kernel_leaf_mapping() was able to handle. The report linked below showed that GIC's ITS was one such user. But during the investigation I found other callsites that could not meet the split_kernel_leaf_mapping() constraints. The problem is that we block map the linear map based on the boot CPU supporting BBML2_NOABORT, then check that all the other CPUs support it too when finalizing the caps. If they don't, then we stop_machine() and split to ptes. For safety, split_kernel_leaf_mapping() previously wouldn't permit splitting until after the caps were finalized. That ensured that if any secondary cpus were running that didn't support BBML2_NOABORT, we wouldn't risk breaking them. I've fix this problem by reducing the black-out window where we refuse to split; there are now 2 windows. The first is from T0 until the page allocator is inititialized. Splitting allocates memory for the page allocator so it must be in use. The second covers the period between starting to online the secondary cpus until the system caps are finalized (this is a very small window). All of the problematic callers are calling __set_memory_enc_dec() before the secondary cpus come online, so this solves the problem. However, one of these callers, swiotlb_update_mem_attributes(), was trying to split before the page allocator was initialized. So I have moved this call from arch_mm_preinit() to mem_init(), which solves the ordering issue. I've added warnings and return an error if any attempt is made to split in the black-out windows. Note there are other issues which prevent booting all the way to user space, which will be fixed in subsequent patches. Reported-by: Jinjiang Tu <tujinjiang@huawei.com> Closes: https://lore.kernel.org/all/0b2a4ae5-fc51-4d77-b177-b2e9db74f11d@huawei.com/ Fixes:a166563e7e("arm64: mm: support large block mapping when rodata=full") Cc: stable@vger.kernel.org Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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