On Mon, 2024-03-25 at 12:39 +0200, Kirill A. Shutemov wrote: > 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 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@xxxxxxxxxxxxxxx> > Reviewed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> > Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx> _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
