Re: [PATCH v4] arm64: mm: fix linear mem mapping access performance degradation

[Mike Rapoport]

On Tue, Jul 05, 2022 at 01:11:16PM +0100, Will Deacon wrote:
> On Tue, Jul 05, 2022 at 08:07:07PM +0800, guanghui.fgh wrote:
> > 
> > 3.When rodata full is disabled, crashkernel also need protect(keep
> > arch_kexec_[un]protect_crashkres using).
> > I think crashkernel should't depend on radata full(Maybe other architecture
> > don't support radata full now).
> 
> I think this is going round in circles :/
> 
> As a first step, can we please leave the crashkernel mapped unless
> rodata=full? It should be a much simpler patch to write, review and maintain
> and it gives you the performance you want when crashkernel is being used.

As it seems I failed to communicate my thoughts about reusing the existing
unmap_hotplug_range() to remap the crash kernel, let's try a more formal
approach ;-)

This is what I came up with and it does not look too complex. There are a
couple of extra #ifdefs that can be removed if we toss some code around in
a preparation patch.