Re: [PATCH 28/37] x86/mm/pti: Map kernel-text to user-space on 32 bit kernels

[Joerg Roedel]

On Mon, Apr 23, 2018 at 10:09:19AM -0700, Kees Cook wrote:
> On Mon, Apr 23, 2018 at 8:47 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote:
> > From: Joerg Roedel <jroedel@xxxxxxx>
> >
> > Keeping the kernel text mapped with G bit set keeps its
> > entries in the TLB across kernel entry/exit and improved the
> > performance. The 64 bit x86 kernels already do this when
> > there is no PCID, so do this in 32 bit as well since PCID is
> > not even supported there.
> 
> I think this should keep at least part of the logic as 64-bit since
> there are other reasons to turn off the Global flag:
> 
> https://lkml.kernel.org/r/20180420222026.D0B4AAC9@xxxxxxxxxxxxxxxxxx

That patch you linked is for function pti_kernel_image_global_ok() which
is used on 32 bit too. So any logic implemented for 64 bit to turn off
the global bit will automatically be used on 32 bit.


Regards,

	Joerg