* Jörg Rödel (jroedel@xxxxxxx) wrote: > On Tue, Mar 21, 2023 at 09:43:48AM -0400, James Bottomley wrote: > > Could you describe these incompatible goals and explain why you think > > they are incompatible (as in why you and AMD don't think you can agree > > on it)? That would help the rest of us understand where the two SVSM > > implementations fit in our ongoing plans. > > The goal of COCONUT is to have an SVSM which has isolation capabilities > within itself. It already has percpu page-tables and in the end it will > be able to run services (like the TPM) as separate processes in ring 3 > using cooperative multitasking. > > With the current linux-svsm code-base this is difficult to achieve due > to its reliance on the x86-64 crate. For supporting a user-space like > execution mode the crate has too many limitations, mainly in its > page-table and IDT implementations. > > The IDT code from that crate, which is also used in linux-svsm, relies > on compiler-generated entry-code. This is not enough to support a > ring-3 execution mode with syscalls and several (possibly nested) IST > vectors. The next problem with the IDT code is that it doesn't allow > modification of return register state. This makes it impossible to > implement exception fixups to guard RMPADJUST instructions and VMPL1 > memory accesses in general. I'm curious why you're doing isolation using ring-3 stuff rather than another VMPL level? Dave > When we looked at the crate, the page-table implementation supported > basically a direct and an offset mapping, which will get us into > problems when support for non-contiguous mappings or sharing parts of a > page-table with another page-table is needed. So in the very beginning > of the project I decided to go with my own page-table implementation. > > Of course we could start changing linux-svsm to support the same goals, > but I think the end result will not be very different from what COCONUT > looks now. > > Regards, > > -- > Jörg Rödel > jroedel@xxxxxxx > > SUSE Software Solutions Germany GmbH > Frankenstraße 146 > 90461 Nürnberg > Germany > > (HRB 36809, AG Nürnberg) > Geschäftsführer: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman > -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
