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TDX guests allocate shared buffers to perform I/O. It is done by allocating pages normally from the buddy allocator and converting them to shared with set_memory_decrypted(). The second, kexec-ed kernel has no idea what memory is converted this way. It only sees E820_TYPE_RAM. Accessing shared memory via private mapping is fatal. It leads to unrecoverable TD exit. On kexec, walk direct mapping and convert all shared memory back to private. It makes all RAM private again and second kernel may use it normally. The conversion occurs in two steps: stopping new conversions and unsharing all memory. In the case of normal kexec, the stopping of conversions takes place while scheduling is still functioning. This allows for waiting until any ongoing conversions are finished. The second step is carried out when all CPUs except one are inactive and interrupts are disabled. This prevents any conflicts with code that may access shared memory. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Reviewed-by: Kai Huang <kai.huang@intel.com> Tested-by: Tao Liu <ltao@redhat.com> Link: https://lore.kernel.org/r/20240614095904.1345461-12-kirill.shutemov@linux.intel.com |
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| .. | ||
| Makefile | ||
| tdcall.S | ||
| tdx-shared.c | ||
| tdx.c | ||