2006-03-08 02:35:25

by Chris Mason

Subject: [PATCH] fix kexec asm

From: Michael Matz <[email protected]>

While testing kexec and kdump we hit problems where the new kernel would
freeze or instantly reboot. The easiest way to trigger it was to kexec a
kernel compiled for CONFIG_M586 on an athlon cpu. Compiling
for CONFIG_MK7 instead would work fine.

The patch below fixes a few problems with the kexec inline asm.

Signed-off-by: Chris Mason <[email protected]>

---

diff -urp linux-2.6.15.suse/arch/i386/kernel/machine_kexec.c linux-2.6.15/arch/i386/kernel/machine_kexec.c
--- linux-2.6.15.suse/arch/i386/kernel/machine_kexec.c 2006-01-03 04:21:10.000000000 +0100
+++ linux-2.6.15/arch/i386/kernel/machine_kexec.c 2006-02-08 04:19:13.000000000 +0100
@@ -116,13 +116,13 @@ static void load_segments(void)
__asm__ __volatile__ (
"\tljmp $"STR(__KERNEL_CS)",$1f\n"
"\t1:\n"
- "\tmovl $"STR(__KERNEL_DS)",%eax\n"
- "\tmovl %eax,%ds\n"
- "\tmovl %eax,%es\n"
- "\tmovl %eax,%fs\n"
- "\tmovl %eax,%gs\n"
- "\tmovl %eax,%ss\n"
- );
+ "\tmovl $"STR(__KERNEL_DS)",%%eax\n"
+ "\tmovl %%eax,%%ds\n"
+ "\tmovl %%eax,%%es\n"
+ "\tmovl %%eax,%%fs\n"
+ "\tmovl %%eax,%%gs\n"
+ "\tmovl %%eax,%%ss\n"
+ ::: "eax", "memory");
#undef STR
#undef __STR
}
diff -urp linux-2.6.15.suse/arch/x86_64/kernel/machine_kexec.c linux-2.6.15/arch/x86_64/kernel/machine_kexec.c
--- linux-2.6.15.suse/arch/x86_64/kernel/machine_kexec.c 2006-01-03 04:21:10.000000000 +0100
+++ linux-2.6.15/arch/x86_64/kernel/machine_kexec.c 2006-02-08 04:21:13.000000000 +0100
@@ -140,7 +140,7 @@ static void load_segments(void)
"\tmovl %0,%%ss\n"
"\tmovl %0,%%fs\n"
"\tmovl %0,%%gs\n"
- : : "a" (__KERNEL_DS)
+ : : "a" (__KERNEL_DS) : "memory"
);
}

diff -urp linux-2.6.15.suse/include/asm-powerpc/kexec.h linux-2.6.15/include/asm-powerpc/kexec.h
--- linux-2.6.15.suse/include/asm-powerpc/kexec.h 2006-02-08 04:10:24.000000000 +0100
+++ linux-2.6.15/include/asm-powerpc/kexec.h 2006-02-08 04:31:15.000000000 +0100
@@ -93,7 +93,8 @@ static inline void crash_setup_regs(stru
"mfxer %0\n"
"std %0, 296(%2)\n"
: "=&r" (tmp1), "=&r" (tmp2)
- : "b" (newregs));
+ : "b" (newregs)
+ : "memory");
}
}
#else

2006-03-08 04:18:06

by Eric W. Biederman

Subject: Re: [PATCH] fix kexec asm

Chris Mason <[email protected]> writes:

> From: Michael Matz <[email protected]>
>
> While testing kexec and kdump we hit problems where the new kernel would
> freeze or instantly reboot. The easiest way to trigger it was to kexec a
> kernel compiled for CONFIG_M586 on an athlon cpu. Compiling
> for CONFIG_MK7 instead would work fine.
>
> The patch below fixes a few problems with the kexec inline asm.

Thanks. Specifying the stomp of %eax in load_segments is definitely
good. The memory stomp looks excessive and if this was a fast path
I would worry about it. As it is better safe than sorry.

Acked-By: Eric Biederman <[email protected]>

Eric

2006-03-09 09:36:04

by Pavel Machek

Subject: Re: [PATCH] fix kexec asm

On ?t 07-03-06 21:16:34, Eric W. Biederman wrote:
> Chris Mason <[email protected]> writes:
>
> > From: Michael Matz <[email protected]>
> >
> > While testing kexec and kdump we hit problems where the new kernel would
> > freeze or instantly reboot. The easiest way to trigger it was to kexec a
> > kernel compiled for CONFIG_M586 on an athlon cpu. Compiling
> > for CONFIG_MK7 instead would work fine.
> >
> > The patch below fixes a few problems with the kexec inline asm.
>
> Thanks. Specifying the stomp of %eax in load_segments is definitely
> good. The memory stomp looks excessive and if this was a fast path
> I would worry about it. As it is better safe than sorry.

Why excessive? It reloads %ss, AFAICS; at that point, all the stack
potentially changes from gcc's POV.
Pavel
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