kexec: load-preserve-context option on s390

kexec: load-preserve-context option on s390

[Michael Holzheu]

Hello Simon,

I think the --load-preserve-context and --load-jump-back-helper kexec
options are not working on s390 because we do not support
CONFIG_KEXEC_JUMP. I assume the same is true also on other
architectures. Correct me, if I am wrong. Unfortunately I did not find
much documentation for that feature.

Wouldn't it be better to print an error message when the options are
used on those architectures?

Michael



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Re: kexec: load-preserve-context option on s390

[Simon Horman]

On Mon, Sep 26, 2011 at 03:09:09PM +0200, Michael Holzheu wrote:
> Hello Simon,
> 
> I think the --load-preserve-context and --load-jump-back-helper kexec
> options are not working on s390 because we do not support
> CONFIG_KEXEC_JUMP. I assume the same is true also on other
> architectures. Correct me, if I am wrong. Unfortunately I did not find
> much documentation for that feature.
> 
> Wouldn't it be better to print an error message when the options are
> used on those architectures?

Ideally it would be nice if kexec-tools could ask the kernel
if KEXEC_JUMP is supported (or enabled?) or not rather than
hardcoding this information into kexec-tools on a per-architecture basis.

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Re: kexec: load-preserve-context option on s390

[Vivek Goyal]

On Thu, Sep 29, 2011 at 08:51:02AM +0900, Simon Horman wrote:
> On Mon, Sep 26, 2011 at 03:09:09PM +0200, Michael Holzheu wrote:
> > Hello Simon,
> > 
> > I think the --load-preserve-context and --load-jump-back-helper kexec
> > options are not working on s390 because we do not support
> > CONFIG_KEXEC_JUMP. I assume the same is true also on other
> > architectures. Correct me, if I am wrong. Unfortunately I did not find
> > much documentation for that feature.
> > 
> > Wouldn't it be better to print an error message when the options are
> > used on those architectures?
> 
> Ideally it would be nice if kexec-tools could ask the kernel
> if KEXEC_JUMP is supported (or enabled?) or not rather than
> hardcoding this information into kexec-tools on a per-architecture basis.

Shouldn't kexec system call return error if KEXEC_JUMP is not supported
and user asked for it?

Thanks
Vivek

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Re: kexec: load-preserve-context option on s390

[Michael Holzheu]

Hello Vivec,

On Thu, 2011-09-29 at 09:32 -0400, Vivek Goyal wrote:
> On Thu, Sep 29, 2011 at 08:51:02AM +0900, Simon Horman wrote:
> > On Mon, Sep 26, 2011 at 03:09:09PM +0200, Michael Holzheu wrote:
> > > Hello Simon,
> > > 
> > > I think the --load-preserve-context and --load-jump-back-helper kexec
> > > options are not working on s390 because we do not support
> > > CONFIG_KEXEC_JUMP. I assume the same is true also on other
> > > architectures. Correct me, if I am wrong. Unfortunately I did not find
> > > much documentation for that feature.
> > > 
> > > Wouldn't it be better to print an error message when the options are
> > > used on those architectures?
> > 
> > Ideally it would be nice if kexec-tools could ask the kernel
> > if KEXEC_JUMP is supported (or enabled?) or not rather than
> > hardcoding this information into kexec-tools on a per-architecture basis.
> 
> Shouldn't kexec system call return error if KEXEC_JUMP is not supported
> and user asked for it?

I think currently not. I assume that we should check the
KEXEC_PRESERVE_CONTEXT flag in the kexec_load system call.

What about the following:
---
 kernel/kexec.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -949,6 +949,10 @@ SYSCALL_DEFINE4(kexec_load, unsigned lon
 	if (!capable(CAP_SYS_BOOT))
 		return -EPERM;
 
+#ifndef CONFIG_KEXEC_JUMP
+	if (flags & KEXEC_PRESERVE_CONTEXT)
+		return -EOPNOTSUPP;
+#endif
 	/*
 	 * Verify we have a legal set of flags
 	 * This leaves us room for future extensions.




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Re: kexec: load-preserve-context option on s390

[Vivek Goyal]

On Thu, Sep 29, 2011 at 03:38:31PM +0200, Michael Holzheu wrote:
> Hello Vivec,

Right spelling is "Vivek" and not "Vivec" :-)

[..]
> > Shouldn't kexec system call return error if KEXEC_JUMP is not supported
> > and user asked for it?
> 
> I think currently not. I assume that we should check the
> KEXEC_PRESERVE_CONTEXT flag in the kexec_load system call.
> 

Shouldn't following existing code take care of this already?

        /*
         * Verify we have a legal set of flags
         * This leaves us room for future extensions.
         */
        if ((flags & KEXEC_FLAGS) != (flags & ~KEXEC_ARCH_MASK))
                return -EINVAL;

In include/linux/kexec.h, we have following.

/* List of defined/legal kexec flags */
#ifndef CONFIG_KEXEC_JUMP
#define KEXEC_FLAGS    KEXEC_ON_CRASH
#else
#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT)
#endif

Not sure why it is not working.

Thanks
Vivek

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Re: kexec: load-preserve-context option on s390

[Michael Holzheu]

Hello Vivek,

On Fri, 2011-09-30 at 12:06 -0400, Vivek Goyal wrote:
> On Thu, Sep 29, 2011 at 03:38:31PM +0200, Michael Holzheu wrote:
> > Hello Vivec,
> 
> Right spelling is "Vivek" and not "Vivec" :-)

I know... and I really wanted to avoid that error. But somehow the "c"
is always coming automatically :-)

> [..]
> > > Shouldn't kexec system call return error if KEXEC_JUMP is not supported
> > > and user asked for it?
> > 
> > I think currently not. I assume that we should check the
> > KEXEC_PRESERVE_CONTEXT flag in the kexec_load system call.
> > 
> 
> Shouldn't following existing code take care of this already?
> 
>         /*
>          * Verify we have a legal set of flags
>          * This leaves us room for future extensions.
>          */
>         if ((flags & KEXEC_FLAGS) != (flags & ~KEXEC_ARCH_MASK))
>                 return -EINVAL;
> 
> In include/linux/kexec.h, we have following.
> 
> /* List of defined/legal kexec flags */
> #ifndef CONFIG_KEXEC_JUMP
> #define KEXEC_FLAGS    KEXEC_ON_CRASH
> #else
> #define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT)
> #endif
> 
> Not sure why it is not working.

Hmmm, actually it is working. I somehow must have overlooked that
before.

When I call kexec with --load-preserve-context - while not really
knowing what I am doing here - I get the following:

# kexec -p /boot/vmlinuz --load-preserve-context --mem-min=0x10000
--mem-max=0x100000000 

kexec_load failed: Invalid argument
entry       = 0x10000 flags = 160002
nr_segments = 2
segment[0].buf   = 0x3fffc989010
segment[0].bufsz = 330600
segment[0].mem   = 0x10000
segment[0].memsz = 331000
segment[1].buf   = (nil)
segment[1].bufsz = 0
segment[1].mem   = 0x341000
segment[1].memsz = 334be000

Perhaps a better error message could help here. But there are several
possible reasons for getting EINVAL from kexec_load(). So probably we
can't say "--load-preserve-context not supported by current kernel"
every time we get EINVAL from kexec_load().

Not sure what to do here. Perhaps we just leave it as it is.

BTW: Is there any good documentation on KEXEC_PRESERVE_CONTEXT?

Michael


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Re: kexec: load-preserve-context option on s390

[Vivek Goyal]

On Tue, Oct 04, 2011 at 04:07:06PM +0200, Michael Holzheu wrote:

[..]
> > Not sure why it is not working.
> 
> Hmmm, actually it is working. I somehow must have overlooked that
> before.
> 
> When I call kexec with --load-preserve-context - while not really
> knowing what I am doing here - I get the following:
> 
> # kexec -p /boot/vmlinuz --load-preserve-context --mem-min=0x10000
> --mem-max=0x100000000 
> 
> kexec_load failed: Invalid argument
> entry       = 0x10000 flags = 160002
> nr_segments = 2
> segment[0].buf   = 0x3fffc989010
> segment[0].bufsz = 330600
> segment[0].mem   = 0x10000
> segment[0].memsz = 331000
> segment[1].buf   = (nil)
> segment[1].bufsz = 0
> segment[1].mem   = 0x341000
> segment[1].memsz = 334be000
> 
> Perhaps a better error message could help here. But there are several
> possible reasons for getting EINVAL from kexec_load(). So probably we
> can't say "--load-preserve-context not supported by current kernel"
> every time we get EINVAL from kexec_load().
> 
> Not sure what to do here. Perhaps we just leave it as it is.

I am also not sure what can we do here. There are many cases where -EINVAL
can happen.

> 
> BTW: Is there any good documentation on KEXEC_PRESERVE_CONTEXT?

I am not aware of any and really wished there was one

Huang, is there any? Also is anybody using KEXEC_PRESERVE_CONTEXT? I have
not encountered any users yet.

Thanks
Vivek

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