[PATCH v3 3/7] arm64: split off early mapping code from early_fixmap_init()

[Ard Biesheuvel]

On 8 December 2015 at 14:51, Will Deacon <will.deacon at arm.com> wrote:
> On Tue, Dec 08, 2015 at 02:29:33PM +0100, Ard Biesheuvel wrote:
>> On 8 December 2015 at 13:40, Will Deacon <will.deacon at arm.com> wrote:
>> > On Thu, Dec 03, 2015 at 12:18:40PM +0000, Mark Rutland wrote:
>> >> Apologies that it's taken me so long to get around to this...
>> >>
>> >> On Mon, Nov 16, 2015 at 12:23:14PM +0100, Ard Biesheuvel wrote:
>> >> > This splits off and generalises the population of the statically
>> >> > allocated fixmap page tables so that we may reuse it later for
>> >> > the linear mapping once we move the kernel text mapping out of it.
>> >> >
>> >> > This also involves taking into account that table entries at any of
>> >> > the levels we are populating may have been populated already, since
>> >> > the fixmap mapping might not be disjoint up to the pgd level anymore
>> >> > from other early mappings.
>> >>
>> >> As a heads-up, for avoiding TLB conflicts, I'm currently working on
>> >> alternative way of creating the kernel page tables which will definitely
>> >> conflict here, and may or may not supercede this approach.
>> >
>> > Given that the Christmas break is around the corner and your TLB series
>> > is probably going to take some time to get right, I suggest we persevere
>> > with Ard's current patch series for 4.5 and merge the TLB conflict solution
>> > for 4.6. I don't want us to end up in a situation where this is needlessly
>> > blocked on something that isn't quite ready.
>> >
>> > Any objections? If not, Ard -- can you post a new version of this, please?
>> >
>>
>> Happy to post a new version, with the following remarks
>> - my current private tree has evolved in the mean time, and I am now
>> putting the kernel image at the base of the vmalloc region (and the
>> module region right before)
>> - I think Mark's changes would allow me to deobfuscate the VA bias
>> that redirects __va() translations into the kernel VA space rather
>> than the linear mapping
>
> I'll leave that up to you. I'm just trying to avoid you growing a dependency
> on something that's unlikely to make it for 4.5. If Mark separates out the
> parts you need, perhaps that offers us some middle ground.
>

I have played around with Mark's code a bit, and it looks like it's a
huge improvement for the split VA patches as well: I have a patch that
removes early_fixmap_init's dependency on the linear mapping, and
combined with Mark's patches to use the fixmap for manipulating the
page tables, it looks like I no longer need the VA bias to redirect
__va translations into the kernel mapping early on.