[PATCH] 2.6.21 - VMI logic error

[PATCH] 2.6.21 - VMI logic error

[Zachary Amsden]

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So there is a logic error that would prevent us from ever using NOP 
relocations, thus stopping any unnecessary callouts into a VMI ROM.  It 
doesn't affect us so much, but could conceivably affect open source 
implementations of a VMI ROM in the future.  It is not absolutely 
critical, but it would be extremely nice to get it fixed in 2.6.21 so 
there are no broken older kernels floating around that mandate having a 
workaround for this or else breaking compatibility with these kernels.

Thanks,

Zach

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Fix logic error in VMI relocation processing.  NOPs would always cause
a BUG_ON to fire because the != RELOCATION_NONE in the first if clause
precluding the == VMI_RELOCATION_NOP in the second clause.  Make these
direct equality tests and just warn for unsupported relocation types
(which should never happen), falling back to native in that case.

Thanks to Anthony Liguori for noting this!

Signed-off-by: Zachary Amsden <zach@vmware.com>

diff -r 99800d11a3ec arch/i386/kernel/vmi.c
--- a/arch/i386/kernel/vmi.c	Thu Apr 12 16:37:29 2007 -0700
+++ b/arch/i386/kernel/vmi.c	Thu Apr 12 19:00:46 2007 -0700
@@ -685,11 +685,14 @@ do {								\
 do {								\
 	reloc = call_vrom_long_func(vmi_rom, get_reloc,		\
 				    VMI_CALL_##vmicall);	\
-	if (rel->type != VMI_RELOCATION_NONE) {			\
-		BUG_ON(rel->type != VMI_RELOCATION_CALL_REL);	\
+	if (rel->type == VMI_RELOCATION_CALL_REL) 		\
 		paravirt_ops.opname = (void *)rel->eip;		\
-	} else if (rel->type == VMI_RELOCATION_NOP) 		\
+	else if (rel->type == VMI_RELOCATION_NOP) 		\
 		paravirt_ops.opname = (void *)vmi_nop;		\
+	else if (rel->type != VMI_RELOCATION_NONE)		\
+		printk(KERN_WARNING "VMI: Unknown relocation "	\
+				    "type %d for " #vmicall"\n",\
+					rel->type);		\
 } while (0)
 
 /*

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Re: [PATCH] 2.6.21 - VMI logic error

[Andi Kleen]

On Friday 13 April 2007 04:28:46 Zachary Amsden wrote:
> So there is a logic error that would prevent us from ever using NOP 
> relocations, thus stopping any unnecessary callouts into a VMI ROM.  It 
> doesn't affect us so much, but could conceivably affect open source 
> implementations of a VMI ROM in the future.  It is not absolutely 
> critical, but it would be extremely nice to get it fixed in 2.6.21 so 
> there are no broken older kernels floating around that mandate having a 
> workaround for this or else breaking compatibility with these kernels.

Patch is fine for me.

-Andi