Hi Kirill, On Thu, Jul 22, 2021 at 10:51:30PM +0300, Kirill A. Shutemov wrote: > Okay, below is my first take on the topic. Thanks, I havn't looked deeply into the patch yet, but will do so tomorrow and reply separatly. > I ended up combing your idea with bitmap with PageOffline(): early boot > code uses bitmap, but on page allocator init I mark unaccepted pages with > PageOffline(). This way page allocator need to touch the bitmap only when > it steps on PageOffline() which shouldn't be often once things settle > after boot. I still need to understand the benefit of having this information in the memmap, but I also don't object to it. For AMD-SNP the bitmap needs to stay around at least, unless there is another way to implement kexec/kdump. > One bit in the bitmap represents 2M region. Any unaligned chunks gets > accepted when we construct the bitmap. This way one 4K page can represent > 64 GiB of physical address space. Yeah, a 2MB chunk size makes sense when it comes to how much we validate at once. I think it will be good choice for AMD too. On the other side there is a need for SNP to track shared pages on a 4k granularity. There are a couple of shared (or at least not valid) pages (GHCB, #HV shared page, VMSA page) per vCPU which are 4k in size. Oh, and then there is the .bss_decrypted section, which is also not 2M aligend. In case of kexec/kdump this information needs to be passed on to the next kernel. Regards, Jörg
