On Thu, Mar 9, 2017 at 1:43 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote: > On 09/03/2017 21:32, Andy Lutomirski wrote: >> On Mon, Mar 6, 2017 at 2:03 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote: >> >>> --- a/arch/x86/xen/enlighten.c >>> +++ b/arch/x86/xen/enlighten.c >>> @@ -710,7 +710,7 @@ static void load_TLS_descriptor(struct thread_struct *t, >>> >>> *shadow = t->tls_array[i]; >>> >>> - gdt = get_cpu_gdt_table(cpu); >>> + gdt = get_cpu_gdt_rw(cpu); >>> maddr = arbitrary_virt_to_machine(&gdt[GDT_ENTRY_TLS_MIN+i]); >>> mc = __xen_mc_entry(0); >> Boris, is this right? I don't see why it wouldn't be, but Xen is special. > > Under Xen PV, the GDT is already read-only at this point. (It is not > safe to let the guest have writeable access to system tables, so the > guest must relinquish write access to the frames wishing to be used as > LDTs or GDTs.) > > The hypercall acts on the frame, not a virtual address, so either alias > should be fine here. > > Under this new scheme, there will be two read-only aliases. I guess > this is easier to maintain the split consistently across Linux, than to > special case Xen PV because it doesn't need the second alias. > I think we would gain nothing at all by special-casing Xen PV -- Linux allocates the fixmap vaddrs at compile time, so we'd still allocate them even if we rejigger all the helpers to avoid using them. --Andy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
