Re: Kernel Oops with kvm 66 running WinXP

Avi Kivity
2008-05-05T12:00:33Z

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Michal Ludvig wrote:
>>>
>>> loaded kvm module (kvm-68)
>>> kvm: emulating exchange as write
>>> Unable to handle kernel NULL pointer dereference at 0000000000000000
>>> RIP:
>>> [<ffffffff88373b4a>] :kvm:x86_emulate_insn+0x3fa/0x4240
>>
>> Please apply the attached patch, and post 'dmesg | grep writeback'.
>
> writeback: b 01 mordm e0
>

Ah, it only affects pre-npt, so my testing was worthless. The attached
patch should fix.

--
error compiling committee.c: too many arguments to function

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diff --git a/kernel/x86_emulate.c b/kernel/x86_emulate.c
index f2a696d..8a96320 100644
--- a/kernel/x86_emulate.c
+++ b/kernel/x86_emulate.c
@@ -677,8 +677,9 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
c->use_modrm_ea = 1;

if (c->modrm_mod == 3) {
- c->modrm_val = *(unsigned long *)
- decode_register(c->modrm_rm, c->regs, c->d & ByteOp);
+ c->modrm_ptr = decode_register(c->modrm_rm,
+ c->regs, c->d & ByteOp);
+ c->modrm_val = *(unsigned long *)c->modrm_ptr;
return rc;
}

@@ -1005,6 +1006,7 @@ done_prefixes:
if ((c->d & ModRM) && c->modrm_mod == 3) {
c->src.type = OP_REG;
c->src.val = c->modrm_val;
+ c->src.ptr = c->modrm_ptr;
break;
}
c->src.type = OP_MEM;
@@ -1049,6 +1051,7 @@ done_prefixes:
if ((c->d & ModRM) && c->modrm_mod == 3) {
c->dst.type = OP_REG;
c->dst.val = c->dst.orig_val = c->modrm_val;
+ c->dst.ptr = c->modrm_ptr;
break;
}
c->dst.type = OP_MEM;
diff --git a/include/asm-x86/kvm_x86_emulate.h b/include/asm-x86/kvm_x86_emulate.h
index d6337f9..b877bbd 100644
--- a/kernel/include/asm-x86/kvm_x86_emulate.h
+++ b/kernel/include/asm-x86/kvm_x86_emulate.h
@@ -135,6 +135,7 @@ struct decode_cache {
u8 modrm_rm;
u8 use_modrm_ea;
unsigned long modrm_ea;
+ void *modrm_ptr;
unsigned long modrm_val;
struct fetch_cache fetch;
};

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