[RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86_64

[RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86_64

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rjw@sisk.pl>

On x86_64 the configuration and version of the kernel that
hibernates and creates a system image may be different from the
configuration and version of the boot kernel that loads the image.
So long as both these kernels are built with the same value of
RESTORE_MAGIC, the image created by one of them should be
successfully loaded and restored by the other one.

It wasn't necessary to modify RESTORE_MAGIC in the past, but now
that we are adding compression to the in-kernel hibernate code,
change the value of RESTORE_MAGIC so that earlier kernels don't
try to load compressed images they can't handle.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 arch/x86/power/hibernate_64.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/arch/x86/power/hibernate_64.c
===================================================================
--- linux-2.6.orig/arch/x86/power/hibernate_64.c
+++ linux-2.6/arch/x86/power/hibernate_64.c
@@ -137,7 +137,7 @@ struct restore_data_record {
 	unsigned long magic;
 };
 
-#define RESTORE_MAGIC	0x0123456789ABCDEFUL
+#define RESTORE_MAGIC	0x0123456789ABCDF0UL
 
 /**
  *	arch_hibernation_header_save - populate the architecture specific part

Re: [RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86_64

[H. Peter Anvin]

On 09/28/2010 04:12 PM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@sisk.pl>
> 
> On x86_64 the configuration and version of the kernel that
> hibernates and creates a system image may be different from the
> configuration and version of the boot kernel that loads the image.
> So long as both these kernels are built with the same value of
> RESTORE_MAGIC, the image created by one of them should be
> successfully loaded and restored by the other one.
> 
> It wasn't necessary to modify RESTORE_MAGIC in the past, but now
> that we are adding compression to the in-kernel hibernate code,
> change the value of RESTORE_MAGIC so that earlier kernels don't
> try to load compressed images they can't handle.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> ---
>  arch/x86/power/hibernate_64.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/arch/x86/power/hibernate_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/power/hibernate_64.c
> +++ linux-2.6/arch/x86/power/hibernate_64.c
> @@ -137,7 +137,7 @@ struct restore_data_record {
>  	unsigned long magic;
>  };
>  
> -#define RESTORE_MAGIC	0x0123456789ABCDEFUL
> +#define RESTORE_MAGIC	0x0123456789ABCDF0UL
>  

Two issues with this:

a) shouldn't we only set this when the image is actually compressed?

b) using systematic magics like this is pessimal in terms of collision
avoidance.  It's much better to use a true random number.

Hence, I propose:

: anacreon 95 ; ranpwd -xc 16
0x4ddedd3236f1e6e1

	-hpa

Re: [RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86_64

[Rafael J. Wysocki]

On Wednesday, September 29, 2010, H. Peter Anvin wrote:
> On 09/28/2010 04:12 PM, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@sisk.pl>
> > 
> > On x86_64 the configuration and version of the kernel that
> > hibernates and creates a system image may be different from the
> > configuration and version of the boot kernel that loads the image.
> > So long as both these kernels are built with the same value of
> > RESTORE_MAGIC, the image created by one of them should be
> > successfully loaded and restored by the other one.
> > 
> > It wasn't necessary to modify RESTORE_MAGIC in the past, but now
> > that we are adding compression to the in-kernel hibernate code,
> > change the value of RESTORE_MAGIC so that earlier kernels don't
> > try to load compressed images they can't handle.
> > 
> > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> > ---
> >  arch/x86/power/hibernate_64.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Index: linux-2.6/arch/x86/power/hibernate_64.c
> > ===================================================================
> > --- linux-2.6.orig/arch/x86/power/hibernate_64.c
> > +++ linux-2.6/arch/x86/power/hibernate_64.c
> > @@ -137,7 +137,7 @@ struct restore_data_record {
> >  	unsigned long magic;
> >  };
> >  
> > -#define RESTORE_MAGIC	0x0123456789ABCDEFUL
> > +#define RESTORE_MAGIC	0x0123456789ABCDF0UL
> >  
> 
> Two issues with this:
> 
> a) shouldn't we only set this when the image is actually compressed?

Well, in fact, this is a workaround, because the compression happens in a
different layer.  However, that other layer doesn't have any compatibility
checks (at least on x86-64), other than seeing that the image metadata
don't make sense at one point.

> b) using systematic magics like this is pessimal in terms of collision
> avoidance.  It's much better to use a true random number.
> 
> Hence, I propose:
> 
> : anacreon 95 ; ranpwd -xc 16
> 0x4ddedd3236f1e6e1

Fine with me, although I don't expect it will be necessary to do that in
the future.

Thanks,
Rafael

Re: [RFC][PATCH] PM / Hibernate / x86: Change RESTORE_MAGIC on x86_64

[Rafael J. Wysocki]

On Wednesday, September 29, 2010, Rafael J. Wysocki wrote:
> On Wednesday, September 29, 2010, H. Peter Anvin wrote:
> > On 09/28/2010 04:12 PM, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rjw@sisk.pl>
> > > 
> > > On x86_64 the configuration and version of the kernel that
> > > hibernates and creates a system image may be different from the
> > > configuration and version of the boot kernel that loads the image.
> > > So long as both these kernels are built with the same value of
> > > RESTORE_MAGIC, the image created by one of them should be
> > > successfully loaded and restored by the other one.
> > > 
> > > It wasn't necessary to modify RESTORE_MAGIC in the past, but now
> > > that we are adding compression to the in-kernel hibernate code,
> > > change the value of RESTORE_MAGIC so that earlier kernels don't
> > > try to load compressed images they can't handle.
> > > 
> > > Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> > > ---
> > >  arch/x86/power/hibernate_64.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > Index: linux-2.6/arch/x86/power/hibernate_64.c
> > > ===================================================================
> > > --- linux-2.6.orig/arch/x86/power/hibernate_64.c
> > > +++ linux-2.6/arch/x86/power/hibernate_64.c
> > > @@ -137,7 +137,7 @@ struct restore_data_record {
> > >  	unsigned long magic;
> > >  };
> > >  
> > > -#define RESTORE_MAGIC	0x0123456789ABCDEFUL
> > > +#define RESTORE_MAGIC	0x0123456789ABCDF0UL
> > >  
> > 
> > Two issues with this:
> > 
> > a) shouldn't we only set this when the image is actually compressed?
> 
> Well, in fact, this is a workaround, because the compression happens in a
> different layer.  However, that other layer doesn't have any compatibility
> checks (at least on x86-64), other than seeing that the image metadata
> don't make sense at one point.

Sorry, I was wrong.  This patch shouldn't be necessary, I'll send another one
that only touches things in kernel/power.

Thanks,
Rafael