Re: [PATCH 12/12] EFI: Runtime services virtual mapping

From: Borislav Petkov
Date: Tue Oct 29 2013 - 05:40:46 EST

On Tue, Oct 29, 2013 at 02:47:20PM +0800, Dave Young wrote:
> Boris, could you update the comment? it says below: update that memory
> descriptor with the virtual address obtained from ioremap().
> Logiclly your patch should update it, then my patch update it again
> with the case of mapping to fixed address for kexec.

Thanks for catching this, I ended up doing the following:

* This function will switch the EFI runtime services to virtual mode.
* Essentially, we look through the EFI memmap and map every region that
* has the runtime attribute bit set in its memory descriptor into the
* ->trampoline_pgd page table using a top-down VA allocation scheme.
* The old method which used to update that memory descriptor with the
* virtual address obtained from ioremap() is still supported when the
* kernel is booted with efi=old_map on its command line. Same old
* method enabled the runtime services to be called without having to
* thunk back into physical mode for every invocation.
* The new method does a pagetable switch in a preemption-safe manner
* so that we're in a different address space when calling a runtime
* function. For function arguments passing we do copy the PGDs of the
* kernel page table into ->trampoline_pgd prior to each call.


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