>>> On 10.04.13 at 02:43, "H. Peter Anvin" <h...@zytor.com> wrote: > OK, thinking about the GDT here. > > The GDT is quite small -- 256 bytes on i386, 128 bytes on x86-64. As > such, we probably don't want to allocate a full page to it for only > that. This means that in order to create a readonly mapping we have to > pack GDTs from different CPUs together in the same pages, *or* we > tolerate that other things on the same page gets reflected in the same > mapping.
I think a read-only GDT is incompatible with exceptions delivered through task gates (i.e. double fault on 32-bit), so I would assume this needs to remain a 64-bit only thing. > However, the packing solution has the advantage of reducing address > space consumption which matters on 32 bits: even on i386 we can easily > burn a megabyte of address space for 4096 processors, but burning 16 > megabytes starts to hurt. Packing would have the additional benefit of Xen not needing to become a special case in yet another area (because pages containing live descriptor table entries need to be read-only for PV guests, and need to consist of only descriptor table entries). Jan _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
