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

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Message-ID: <20131029094033.GA10972@pd.tnic>
Date:	Tue, 29 Oct 2013 10:40:34 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Young <dyoung@...hat.com>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>,
	Matt Fleming <matt@...sole-pimps.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Vivek Goyal <vgoyal@...hat.com>, linux-efi@...r.kernel.org,
	fwts-devel@...ts.ubuntu.com
Subject: Re: [PATCH 12/12] EFI: Runtime services virtual mapping

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.
 */

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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