On Tue, Jun 16, 2020 at 12:24:12PM +0200, Christoph Hellwig wrote:
> On Tue, Jun 16, 2020 at 12:23:50PM +0200, Christoph Hellwig wrote:
> > > + hv_hypercall_pg = module_alloc(PAGE_SIZE);
> > > if (hv_hypercall_pg == NULL) {
> > > wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
> > > goto remove_cpuhp_state;
> > > }
> > >
> > > + set_memory_ro((unsigned long)hv_hypercall_pg, 1);
> > > + set_memory_x((unsigned long)hv_hypercall_pg, 1);
> >
> > The changing of the permissions sucks. I thought about adding
> > a module_alloc_prot with an explicit pgprot_t argument. On x86
> > alone at least ftrace would also benefit from that.
How would ftrace benefit from a RX permission? We need to actually write
to the page first. This HV thing is special in that it lets the host
write.
> The above is also missing a set_vm_flush_reset_perms.
Ah, indeed. Otherwise we don't clean up properly.
