linux-kernel - Re: [PATCH v7 09/12] efi: passing kexec necessary efi data via setup

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Date:	Wed, 25 Dec 2013 11:32:05 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	x86@...nel.org, mjg59@...f.ucam.org, hpa@...or.com,
	James.Bottomley@...senPartnership.com, vgoyal@...hat.com,
	ebiederm@...ssion.com, horms@...ge.net.au,
	kexec@...ts.infradead.org, bp@...en8.de, greg@...ah.com,
	toshi.kani@...com, akpm@...ux-foundation.org, mingo@...nel.org,
	msalter@...hat.com, leif.lindholm@...aro.org
Subject: Re: [PATCH v7 09/12] efi: passing kexec necessary efi data via
 setup_data

On 12/25/13 at 11:12am, Dave Young wrote:
> On 12/23/13 at 08:07am, Matt Fleming wrote:
> > On Mon, 23 Dec, at 10:09:58AM, Dave Young wrote:
> > > On 12/21/13 at 04:06pm, Matt Fleming wrote:
> > > > On Fri, 20 Dec, at 06:02:19PM, Dave Young wrote:
> > > > > @@ -133,6 +133,19 @@ extern void efi_sync_low_kernel_mappings(void);
> > > > >  extern void efi_setup_page_tables(void);
> > > > >  extern void __init old_map_region(efi_memory_desc_t *md);
> > > > >  
> > > > > +struct efi_setup_data {
> > > > > +	u64 fw_vendor;
> > > > > +	u64 runtime;
> > > > > +	u64 tables;
> > > > > +	u64 smbios;
> > > > > +	u64 reserved[8];
> > > > > +	efi_memory_desc_t map[0];
> > > > > +};
> > > > 
> > > > [...]
> > > > 
> > > > > +static void get_nr_runtime_map(void)
> > > > > +{
> > > > > +	if (!efi_setup)
> > > > > +		return;
> > > > > +
> > > > > +	nr_efi_runtime_map = (efi_data_len - sizeof(struct efi_setup_data)) /
> > > > > +			     sizeof(efi_memory_desc_t);
> > > > > +}
> > > > 
> > > > Do we actually need the 'map' entry in efi_setup_data now that you're
> > > > passing it via efi_info (which is much better approach!)? Also, we don't
> > > > need the global nr_efi_runtime_map or efi_runtime_map variables now,
> > > > right?
> > > 
> > > The map is still necessary because we need store the map somewhere and pass
> > > the physicall address to kexec kernel. Passing them in setup_data is the
> > > only better way currently...
> > > 
> > > In efi_info there's only an entry for the map physical address, the original
> > > map area is not valid any more.
> > 
> > Where do you dereference efi_setup_data.map* in the kexec kernel?
> 
> The field itself is not dereferenced in kernel but it's still used in userspace
> code for collecting and saving runtime maps. Since I still append the map at the
> end of efi_setup_data so I think keep the map[0] is ok. What's your opinion?

Matt, if you want to remove the map[0] please fold below one line patch? I have no
strong opinion.

Index: linux/arch/x86/include/asm/efi.h
===================================================================
--- linux.orig/arch/x86/include/asm/efi.h
+++ linux/arch/x86/include/asm/efi.h
@@ -139,7 +139,6 @@ struct efi_setup_data {
 	u64 tables;
 	u64 smbios;
 	u64 reserved[8];
-	efi_memory_desc_t map[0];
 };
 
 extern u64 efi_setup;
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