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

From: Dave Young
Date: Wed Oct 30 2013 - 05:33:07 EST

On 10/29/13 at 10:40am, Borislav Petkov wrote:
> 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.
> */

Boris, thanks for update, it's very elaborate, I have still wonder if
32 bit case should be mentioned as well.

Waiting for you next version of the patch series. I will redo my patches
based on that.

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