> > -------- Forwarded Message --------
> > From: Mohan Kumar M <mohan at in.ibm.com>
> > To: paulus at samba.org
> > Cc: linuxppc-dev at ozlabs.org, kexec at lists.infradead.org
> > Subject: [PATCH] Support for relocatable kdump kernel
> > Date: Mon, 13 Oct 2008 05:04:20 +0530
> >
> > Support for relocatable kdump kernel
> >
> > This patch adds relocatable kernel support for kdump. With this one can
> > use the same regular kernel to capture the kdump. A signature (0xfeed1234)
> > is passed in r8 from panic code to the next kernel through kexec_sequence
> > and purgatory code. The signature is used to differentiate between
> > relocatable kdump kernel and non-kdump kernels.
You should put a big fat warning here in the changelog. By changing the
calling sequence (adding to it), we now require that for a new kernel to
work as a kdump kernel it has to be loaded with new kexec tools.
> > The purgatory code compares the signature and sets the __kdump_flag in
> > head_64.S. During the boot up, kernel code checks __kdump_flag and if it
> > is set, the kernel will behave as relocatable kdump kernel. This kernel
> > will boot at the address where it was loaded by kexec-tools ie at the
> > address reserved through crashkernel boot parameter
> >
> > CONFIG_CRASH_DUMP depends on CONFIG_RELOCATABLE option to build kdump
> > kernel as relocatable. So the same kernel can be used as production and
> > kdump kernel.
Those two statements aren't really related. A CONFIG_RELOCATABLE kernel
can be used as both a kdump and a normal kernel, and we need to make
sure that a CONFIG_CRASH_DUMP kernel can be used as both - ie. that
there's no code that uses CONFIG_CRASH_DUMP to do anything we /don't/
want in a normal kernel.
> > This patch incorporates the changes suggested by Paul Mackerrass to avoid
> > GOT use and to avoid two copies of the code.
> >
> > Signed-off-by: Mohan Kumar M <mohan at in.ibm.com>
> > diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> > index 0705040..3f4bc84 100644
> > --- a/Documentation/kdump/kdump.txt
> > +++ b/Documentation/kdump/kdump.txt
> > @@ -109,7 +109,8 @@ There are two possible methods of using Kdump.
> > 2) Or use the system kernel binary itself as dump-capture kernel and there is
> > no need to build a separate dump-capture kernel. This is possible
> > only with the architecutres which support a relocatable kernel. As
> > - of today, i386, x86_64 and ia64 architectures support relocatable kernel.
> > + of today, i386, x86_64, ppc64 and ia64 architectures support relocatable
> > + kernel.
This is a little bit unclear as the kernel now doesn't have a ppc64
architecture. You might want to say "64-bit powerpc (ppc64)", because
that matches the kernel arch and also kexec-tools (which still has
ppc32/64 IIRC)
> >
> > Building a relocatable kernel is advantageous from the point of view that
> > one does not have to build a second kernel for capturing the dump. But
> > @@ -207,8 +208,15 @@ Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
> > Dump-capture kernel config options (Arch Dependent, ppc64)
> > ----------------------------------------------------------
> >
> > -* Make and install the kernel and its modules. DO NOT add this kernel
> > - to the boot loader configuration files.
> > +1) Enable "Build a kdump crash kernel" support under "Kernel" options:
> > +
> > + CONFIG_CRASH_DUMP=y
> > +
> > +2) Enable "Build a relocatable kernel" support
> > +
> > + CONFIG_RELOCATABLE=y
> > +
> > + Make and install the kernel and its modules.
> >
> > Dump-capture kernel config options (Arch Dependent, ia64)
> > ----------------------------------------------------------
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 17c988b..6b3e840 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -321,11 +321,11 @@ config KEXEC
> >
> > config CRASH_DUMP
> > bool "Build a kdump crash kernel"
> > - depends on PPC_MULTIPLATFORM && PPC64
> > + depends on PPC_MULTIPLATFORM && PPC64 && RELOCATABLE
> > help
> > Build a kernel suitable for use as a kdump capture kernel.
> > - The kernel will be linked at a different address than normal, and
> > - so can only be used for Kdump.
> > + The same kernel binary can be used as production kernel and dump capture
> > + kernel
> >
> > Don't change this unless you know what you are doing.
> >
> > @@ -824,11 +824,9 @@ config PAGE_OFFSET
> > default "0xc000000000000000"
> > config KERNEL_START
> > hex
> > - default "0xc000000002000000" if CRASH_DUMP
> > default "0xc000000000000000"
> > config PHYSICAL_START
> > hex
> > - default "0x02000000" if CRASH_DUMP
> > default "0x00000000"
> > endif
> >
> > diff --git a/arch/powerpc/include/asm/kdump.h b/arch/powerpc/include/asm/kdump.h
> > index f6c93c7..5308754 100644
> > --- a/arch/powerpc/include/asm/kdump.h
> > +++ b/arch/powerpc/include/asm/kdump.h
> > @@ -9,6 +9,12 @@
> > * Reserve to the end of the FWNMI area, see head_64.S */
> > #define KDUMP_RESERVE_LIMIT 0x10000 /* 64K */
> >
> > +/*
> > + * Used to differentiate between relocatable kdump kernel and other
> > + * kernels
> > + */
> > +#define KDUMP_SIGNATURE 0xfeed1234
> > +
> > #ifdef CONFIG_CRASH_DUMP
> >
> > #define KDUMP_TRAMPOLINE_START 0x0100
> > @@ -19,11 +25,21 @@
> > #endif /* CONFIG_CRASH_DUMP */
> >
> > #ifndef __ASSEMBLY__
> > +
> > +extern unsigned long long __kdump_flag;
Why long long ?
> > #ifdef CONFIG_CRASH_DUMP
> > +#ifdef CONFIG_RELOCATABLE
> > +
> > +static inline void reserve_kdump_trampoline(void) { ; }
> > +static inline void setup_kdump_trampoline(void) { ; }
> > +
> > +#else
> >
> > extern void reserve_kdump_trampoline(void);
> > extern void setup_kdump_trampoline(void);
> >
> > +#endif /* CONFIG_RELOCATABLE */
You've disabled the else case with your Kconfig changes, so you should
just rip all that code out.
> > static inline void reserve_kdump_trampoline(void) { ; }
> > diff --git a/arch/powerpc/kernel/crash_dump.c b/arch/powerpc/kernel/crash_dump.c
> > index a323c9b..eaf9d6d 100644
> > --- a/arch/powerpc/kernel/crash_dump.c
> > +++ b/arch/powerpc/kernel/crash_dump.c
> > @@ -27,6 +27,7 @@
> > #define DBG(fmt...)
> > #endif
> >
> > +#ifndef CONFIG_RELOCATABLE
> > void __init reserve_kdump_trampoline(void)
> > {
> > lmb_reserve(0, KDUMP_RESERVE_LIMIT);
> > @@ -65,6 +66,7 @@ void __init setup_kdump_trampoline(void)
> >
> > DBG(" <- setup_kdump_trampoline()\n");
> > }
> > +#endif /* CONFIG_RELOCATABLE */
> >
> > #ifdef CONFIG_PROC_VMCORE
> > static int __init parse_elfcorehdr(char *p)
> > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> > index e409338..5b12b10 100644
> > --- a/arch/powerpc/kernel/head_64.S
> > +++ b/arch/powerpc/kernel/head_64.S
> > @@ -97,6 +97,14 @@ __secondary_hold_spinloop:
> > __secondary_hold_acknowledge:
> > .llong 0x0
> >
> > + /* This flag is set only for kdump kernels so that */
> > + /* it will be relocatable. Purgatory code user space kexec-tools */
> > + /* sets this flag. Do not move this variable as purgatory code */
> > + /* relies on the position of this variables */
> > + .globl __kdump_flag
> > +__kdump_flag:
> > + .llong 0x0
I guess the __ matches the other flags here, it's not the prettiest
though. For client code (like in iommu.c) it'd be nice to have static
inline, perhaps is_kdump_kernel() that hides this.
> > #ifdef CONFIG_PPC_ISERIES
> > /*
> > * At offset 0x20, there is a pointer to iSeries LPAR data.
> > @@ -1384,8 +1392,13 @@ _STATIC(__after_prom_start)
> > /* process relocations for the final address of the kernel */
> > lis r25,PAGE_OFFSET at highest /* compute virtual base of kernel */
> > sldi r25,r25,32
> > +#ifdef CONFIG_CRASH_DUMP
> > + ld r7,__kdump_flag-_stext(r26)
> > + cmpldi cr0,r7,1 /* relocatable kernel ? */
You don't use the signature here?
> > + bne 1f
> > add r25,r25,r26
> > - mr r3,r25
> > +#endif
> > +1: mr r3,r25
> > bl .relocate
> > #endif
> >
> > @@ -1401,9 +1414,21 @@ _STATIC(__after_prom_start)
> > beq 9f /* have already put us at zero */
> > li r6,0x100 /* Start offset, the first 0x100 */
> > /* bytes were copied earlier. */
> > -#ifdef CONFIG_RELOCATABLE
> > +
> > +#ifdef CONFIG_CRASH_DUMP
> > +/*
> > + * Check if the kernel has to be running as relocatable kernel based on the
> > + * variable __kdump_flag, if it is set the kernel is treated as relocatble
> > + * kernel, otherwise it will be moved to PHYSICAL_START
> > + */
> > + ld r7,__kdump_flag-_stext(r26)
> > + cmpldi cr0,r7,1
> > + bne regular
> > +
> > li r5,__end_interrupts - _stext /* just copy interrupts */
> > -#else
> > + b 5f
> > +regular:
> > +#endif
> > lis r5,(copy_to_here - _stext)@ha
> > addi r5,r5,(copy_to_here - _stext)@l /* # bytes of memory to copy */
I'm jet lagged to hell, so I'm not sure I can trust my parsing of this.
But I think this definitely breaks CONFIG_RELOCATABLE without
CRASH_DUMP, and I'm not sure it's right otherwise.
> > @@ -1420,8 +1445,7 @@ p_end: .llong _end - _stext
> > 4: /* Now copy the rest of the kernel up to _end */
> > addis r5,r26,(p_end - _stext)@ha
> > ld r5,(p_end - _stext)@l(r5) /* get _end */
> > -#endif
> > - bl .copy_and_flush /* copy the rest */
> > +5: bl .copy_and_flush /* copy the rest */
> >
> > 9: b .start_here_multiplatform
> >
> > diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> > index 550a193..24f7797 100644
> > --- a/arch/powerpc/kernel/iommu.c
> > +++ b/arch/powerpc/kernel/iommu.c
> > @@ -494,7 +494,7 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid)
> > spin_lock_init(&tbl->it_lock);
> >
> > #ifdef CONFIG_CRASH_DUMP
> > - if (ppc_md.tce_get) {
> > + if (ppc_md.tce_get && __kdump_flag) {
> > unsigned long index;
> > unsigned long tceval;
> > unsigned long tcecount = 0;
I see more code that needs this sort of treatment in pseries/iommu.c and
cell/ras.c
> > diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
> > index aab7688..ac2a21f 100644
> > --- a/arch/powerpc/kernel/machine_kexec.c
> > +++ b/arch/powerpc/kernel/machine_kexec.c
> > @@ -88,11 +88,13 @@ void __init reserve_crashkernel(void)
> >
> > crash_size = crashk_res.end - crashk_res.start + 1;
> >
> > +#ifndef CONFIG_RELOCATABLE
> > if (crashk_res.start != KDUMP_KERNELBASE)
> > printk("Crash kernel location must be 0x%x\n",
> > KDUMP_KERNELBASE);
We still need code here for the RELOCATABLE case that checks a) the
kernel is being allocated inside the RMO, and b) that it's 64k aligned.
> >
> > crashk_res.start = KDUMP_KERNELBASE;
> > +#endif
> > crash_size = PAGE_ALIGN(crash_size);
> > crashk_res.end = crashk_res.start + crash_size - 1;
> >
> > diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
> > index a168514..6a45a9e 100644
> > --- a/arch/powerpc/kernel/machine_kexec_64.c
> > +++ b/arch/powerpc/kernel/machine_kexec_64.c
> > @@ -255,11 +255,13 @@ static union thread_union kexec_stack
> > /* Our assembly helper, in kexec_stub.S */
> > extern NORET_TYPE void kexec_sequence(void *newstack, unsigned long start,
> > void *image, void *control,
> > - void (*clear_all)(void)) ATTRIB_NORET;
> > + void (*clear_all)(void),
> > + unsigned long long kdump_flag) ATTRIB_NORET;
> >
> > /* too late to fail here */
> > void default_machine_kexec(struct kimage *image)
> > {
> > + unsigned long long kdump_flag = 0;
> > /* prepare control code if any */
> >
> > /*
> > @@ -270,8 +272,10 @@ void default_machine_kexec(struct kimage *image)
> > * using debugger IPI.
> > */
> >
> > - if (crashing_cpu == -1)
> > - kexec_prepare_cpus();
> > + if (crashing_cpu == -1)
> > + kexec_prepare_cpus();
> > + else
> > + kdump_flag = KDUMP_SIGNATURE;
> >
> > /* switch to a staticly allocated stack. Based on irq stack code.
> > * XXX: the task struct will likely be invalid once we do the copy!
> > @@ -284,7 +288,7 @@ void default_machine_kexec(struct kimage *image)
> > */
> > kexec_sequence(&kexec_stack, image->start, image,
> > page_address(image->control_code_page),
> > - ppc_md.hpte_clear_all);
> > + ppc_md.hpte_clear_all, kdump_flag);
> > /* NOTREACHED */
> > }
> >
> > diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
> > index 4dd70cf..c93e5f7 100644
> > --- a/arch/powerpc/kernel/misc_64.S
> > +++ b/arch/powerpc/kernel/misc_64.S
> > @@ -609,10 +609,13 @@ real_mode: /* assume normal blr return */
> >
> >
> > /*
> > - * kexec_sequence(newstack, start, image, control, clear_all())
> > + * kexec_sequence(newstack, start, image, control, clear_all(), kdump_flag)
> > *
> > * does the grungy work with stack switching and real mode switches
> > * also does simple calls to other code
> > + *
> > + * kdump_flag says whether the next kernel should be running at the reserved
> > + * load address as needed for relocatable kdump kernel
> > */
Doesn't it just say "we crashed in the first kernel" - what the 2nd
kernel does is up to it.
cheers
--
Michael Ellerman
OzLabs, IBM Australia Development Lab
wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)
We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person
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