linux-kernel - Re: [PATCH -v2] EFI: Runtime services virtual mapping

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Message-ID: <20130925023615.GB7434@dhcp-16-126.nay.redhat.com>
Date:	Wed, 25 Sep 2013 10:36:15 +0800
From:	Dave Young <dyoung@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <bp@...en8.de>, 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>,
	James Bottomley <james.bottomley@...senpartnership.com>,
	Vivek Goyal <vgoyal@...hat.com>, linux-efi@...r.kernel.org
Subject: Re: [PATCH -v2] EFI: Runtime services virtual mapping

On 09/24/13 at 05:12pm, H. Peter Anvin wrote:
> On 09/24/2013 07:56 AM, Borislav Petkov wrote:
> > On Tue, September 24, 2013 2:45 pm, Dave Young wrote:
> >> Think again about this, how about 1:1 map them from a base address
> >> like -64G phy_addr -> (-64G + phy_addr), in this way we can avoid
> >> depending on the previous region size.
> > 
> > Right, how we layout the regions is arbitrary as long as we start at
> > the same VA and use the same regions, in the same order and of the same
> > size...
> > 
> >> For the zero region problem, we can resolve it as a standalone
> >> problem.
> > 
> > ... however, we still need to understand why it fails mapping the boot
> > services region as some implementations apparently do call boot services
> > even after ExitBootServices(). IOW, we need that region mapped in the
> > kexec'ed kernel too.
> > 
> 
> I am starting to think that we really should explicitly pass along the
> EFI mappings to the secondary kernel.  This will also help if we have to
> change the algorithm in a future kernel.

The 0 size mem region is still a problem even we pass the previous mapping
to 2nd kernel. So will be be enough to 1:1 map on high address and leave the
firmware provided memmap not touched, use a copy of memmap in kernel?

> 
> The most logical way to do this is to define a new setup_data type and
> pass the entire set of physical-to-virtual mappings that way.
> 
> For example:
> 
> struct efi_mapping {
> 	u64 va;			/* Virtual start address */
> 	u64 pa;			/* Physical start address */
> 	u64 len;		/* Length in bytes */
> 	u64 type;		/* Mapping type */
> 	u64 reserved[3];	/* Reserved, must be zero */
> };
> 
> Adding some reserved fields seems like a prudent precaution; the map
> shouldn't be all that large anyway.
> 
> 	-hpa
> 
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