On 25.10.20 11:15, Mike Rapoport wrote:
From: Mike Rapoport <rppt@xxxxxxxxxxxxx> Hi, During recent discussion about KVM protected memory, David raised a concern about usage of __kernel_map_pages() outside of DEBUG_PAGEALLOC scope [1]. Indeed, for architectures that define CONFIG_ARCH_HAS_SET_DIRECT_MAP it is possible that __kernel_map_pages() would fail, but since this function is void, the failure will go unnoticed. Moreover, there's lack of consistency of __kernel_map_pages() semantics across architectures as some guard this function with #ifdef DEBUG_PAGEALLOC, some refuse to update the direct map if page allocation debugging is disabled at run time and some allow modifying the direct map regardless of DEBUG_PAGEALLOC settings. This set straightens this out by restoring dependency of __kernel_map_pages() on DEBUG_PAGEALLOC and updating the call sites accordingly.
So, I was primarily wondering if we really have to touch direct mappings in hibernation code, or if we can avoid doing that. I was wondering if we cannot simply do something like kmap() when trying to access a !mapped page. Similar to reading old-os memory after kexec when in kdump. Just a thought.
-- Thanks, David / dhildenb
