Re: [PATCH v7 09/12] efi: passing kexec necessary efi data via setup_data

Dave Young
2013-12-25T03:32:05Z

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;