linux-kernel - Re: [PATCH] export efi.flags to sysfs

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Message-ID: <20140530022438.GC1985@darkstar.nay.redhat.com>
Date:	Fri, 30 May 2014 10:24:38 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	matt.fleming@...el.com, bp@...en8.de, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH] export efi.flags to sysfs

On 05/29/14 at 08:45am, Vivek Goyal wrote:
> On Thu, May 29, 2014 at 10:08:37AM +0800, Dave Young wrote:
> > On 05/28/14 at 08:40am, Vivek Goyal wrote:
> > > On Wed, May 28, 2014 at 10:13:59AM +0800, Dave Young wrote:
> > > > On 05/27/14 at 09:34am, Vivek Goyal wrote:
> > > > > On Mon, May 26, 2014 at 04:39:35PM +0800, Dave Young wrote:
> > > > > > 
> > > > > > For efi=old_map and any old_map quirks like SGI UV in current
> > > > > > tree kexec/kdump will fail because it depends on the new 1:1 mapping.
> > > > > > 
> > > > > > Thus export the mapping method to sysfs so kexec tools can switch
> > > > > > to original way to boot.
> > > > > > 
> > > > > > Since we have efi.flags for all efi facilities so let's just export the
> > > > > > efi.flags itself, it maybe useful for other arches and use cases.
> > > > > > 
> > > > > 
> > > > > Does it require any documentation in Documentation/ABI/..
> > > > 
> > > > Yes, it's necessary. Will do in next version.
> > > > 
> > > > I'm still discussing with Matt, exporting efi.flags seems not a good way
> > > > because they are more internal interfaces. 
> > > > 
> > > > Probably I should export only a file 'old_map' instead.
> > > 
> > > How does /sys/firmware/efi/runtime-map/* look like with old mapping? Can't
> > > we look at it and figure out if it is 1:1 or not.
> > 
> > There's phys_addr and virt_addr, (virt_addr - phys_addr) will always be
> > -64G for 1:1 map, ioremapped addresses space is different.

Correct myself it's top to down (-4G - -64G) instead of down to top. 

> 
> I am curious that what's the meaning of 1:1 mapping here? So far I thought
> that means virt and physical addresses are same but that does not seem
> to be the case. So what does it mean?

while doing the mapping, we will iterate the memory ranges (md[])

Like below without considering alignment:
Virt addr   (down) <------------------------------> (top)
md0 (size0)                                 <-----> 
                                             (size0)
md1 (size1)                        <------->
                                    (size1)
...

Boris can correct me if I'm wrong.

Thanks
Dave
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