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

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Message-ID: <20131013030602.GA1914@darkstar.nay.redhat.com>
Date:	Sun, 13 Oct 2013 11:06:03 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>,
	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 Sat, Oct 12, 2013 at 11:13:08AM +0100, Matt Fleming wrote:
> On Sat, 12 Oct, at 03:54:44PM, Dave Young wrote:
> > Boris:
> > 
> > For the boot service region overlapping problem I have another idea,
> > how about modify your mapping code to always mapping the RUNTIME region
> > (non boot service region) firstly from the efi_va, then mapping other
> > regions in order, in this way kexec 2nd kernel will be happy because
> > it does not call SetVirtualAddressMap and it does not need the boot
> > service area at all.
> 
> Coalescing the runtime regions together implies that the second kernel
> would care about the fragmentation caused by unmapping the boot service
> regions - it shouldn't. We've sliced up a considerable chunk of kernel
> virtual address space (64G) and fragmentation shouldn't be an issue
> right now.
> 
> Even if we run out of address space in the future due to fragmentation,
> and end up needing to coalesce runtime regions, this would be
> transparent to the kexec kernel because it's passed the memmap entries
> through setup_data.

Ok, so passing setup_data looks better like hpa said previously.

> 
> Though we are defining an ABI around the EFI address range
> (0xffffffef00000000 - 0xffffffff00000000), such that it needs to be the
> same between kernels, we must not make the layout of regions within that
> range part of the ABI. We need the freedom to change the layout in the
> future.

Agree.

> 
> -- 
> Matt Fleming, Intel Open Source Technology Center
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