[PATCH] powerpc/mm/radix: Only add X for pages overlapping kernel text

[Michael Ellerman]

Balbir Singh <bsingharora at gmail.com> writes:
> On Tue, Jun 6, 2017 at 3:48 PM, Michael Ellerman <mpe at ellerman.id.au> wrote:
>> Currently we map the whole linear mapping with PAGE_KERNEL_X. Instead we
>> should check if the page overlaps the kernel text and only then add
>> PAGE_KERNEL_X.
...
>> @@ -145,8 +147,14 @@ static int __meminit create_physical_mapping(unsigned long start,
>>                         start = addr;
>>                 }
>>
>> -               rc = radix__map_kernel_page((unsigned long)__va(addr), addr,
>> -                                           PAGE_KERNEL_X, mapping_size);
>> +               vaddr = (unsigned long)__va(addr);
>> +
>> +               if (overlaps_kernel_text(vaddr, vaddr + mapping_size))
>> +                       prot = PAGE_KERNEL_X;
>> +               else
>> +                       prot = PAGE_KERNEL;
>
> Do we need the kvm tmp/trampoline bits like hash?

Ugh, I hope not. What is that crap.

It appears to be epapr paravirt only:

  static int __init kvm_guest_init(void)
  {
  	if (!kvm_para_available())
  		goto free_tmp;
  
  	if (!epapr_paravirt_enabled)
  		goto free_tmp;


But I can't convince myself whether epapr_paravirt_enabled is ever set
on Book3S guests or not.

Looking at Qemu it looks like it *could* be.

And why isn't that code in arch/powerpc/kvm ?

cheers