On Wed, Dec 09, 2020 at 12:27:59PM -0600, Richard Henderson wrote: > On 12/9/20 9:27 AM, Catalin Marinas wrote: > > On Wed, Dec 09, 2020 at 01:25:18PM +0000, Marc Zyngier wrote: > >> Would this syscall operate on the guest address space? Or on the VMM's > >> own mapping? > ... > > Whatever is easier for the VMM, I don't think it matters as long as the > > host kernel can get the actual physical address (and linear map > > correspondent). Maybe simpler if it's the VMM address space as the > > kernel can check the access permissions in case you want to hide the > > guest memory from the VMM for other reasons (migration is also off the > > table). > > Indeed, such a syscall is no longer specific to vmm's and may be used for any > bulk move of tags that userland might want. For CRIU, I think the current ptrace interface would do. With VMMs, the same remote VM model doesn't apply (the "remote" VM is actually the guest memory). I'd keep this under a KVM ioctl() number rather than a new, specific syscall. > > Without syscalls, an option would be for the VMM to create two mappings: > > one with PROT_MTE for migration and the other without for normal DMA > > etc. That's achievable using memfd_create() or shm_open() and two mmap() > > calls, only one having PROT_MTE. The VMM address space should be > > sufficiently large to map two guest IPAs. > > I would have thought that the best way is to use TCO, so that we don't have to > have dual mappings (and however many MB of extra page tables that might imply). The problem appears when the VMM wants to use MTE itself (e.g. linked against an MTE-aware glibc), toggling TCO is no longer generic enough, especially when it comes to device emulation. -- Catalin _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
