On 8/14/22 21:12, Kirill A. Shutemov wrote: > But if somebody would try to be clever -- allocate memory and vmap() as > shared (with proper VMM notification), but leave direct mapping intact -- > we have a problem. load_unaligned_zeropad() can step onto private mapping > of the shared memory in direct mapping and crash whole TD guest. > > The worst part is that for somebody who is not aware about > load_unaligned_zeropad(), the vmap() trick is totally reasonable approach: > it helps to avoid direct mapping fragmentation. We considered the trick > for one of TDX-specific drivers. This can also be fixed with guard pages. It means allocating a physically contiguous page to precede each one you want to vmap(), but that's not the end of the world. We're going to have to be *VERY* careful with any private->shared conversion code.
