Re: KVM 29: Page fault in kernel mode while booting GNU/kFreeBSD

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

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Aurelien Jarno wrote:
> On Sun, Jul 15, 2007 at 09:23:31AM +0300, Avi Kivity wrote:
>   
>> Can you bisect kvm to find the offending commit?  Basically, you do a
>>
>>   git clone git://git.kernel.org/pub/scm/linux/kernel/git/avi/kvm.git
>>   cd kvm
>>   git bisect start drivers/kvm/
>>   bit bisect bad kvm-29
>>   git bisect good kvm-28
>>
>> git will check out a test candidate; go to your kvm userspace directory 
>> and do
>>
>>   make -C kernel sync LINUX=/path/to/the/kvm/git/directory
>>   make -C kernel
>>   sudo make -C kernel install
>>
>> reload the module, test, and issue 'git bisect good' or 'git bisect bad' 
>> according to the result.  As there are only 25 commits you should be 
>> done in 5 cycles.
>>
>>     
>
> And the result is:
>
> commit ba9c20c048726037664d303362b688759fdf6e9d
> Author: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Date:   Tue Jun 19 22:41:20 2007 +0200
>
>     KVM: Fix x86 emulator writeback
>     
>     When the old value and new one are the same the emulator skips the
>     write; this is undesirable when the destination is a MMIO area and the
>     write shall be performed regardless of the previous value. This
>     optimization breaks e.g. a Linux guest APIC compiled without
>     X86_GOOD_APIC.
>     
>     Remove the check and perform the writeback stage in the emulation unless
>     it's explicitly disabled (currently push and some 2 bytes instructions
>     may disable the writeback).
>     
>     Signed-Off-By: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>     Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
>
>
> I have tried to revert this patch directly into kvm-29, and it also
> fixes the problem.
>
>   

 From a cursory inspection, looks like the cmov instructions were broken 
by the patch.  Can you try the attached patch on top of kvm-29?


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


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diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index f60012d..7974012 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1225,40 +1225,40 @@ twobyte_insn:
 		break;
 	case 0x40 ... 0x4f:	/* cmov */
 		dst.val = dst.orig_val = src.val;
-		d &= ~Mov;	/* default to no move */
+		no_wb = 1;	/* default to no move */
 		/*
 		 * First, assume we're decoding an even cmov opcode
 		 * (lsb == 0).
 		 */
 		switch ((b & 15) >> 1) {
 		case 0:	/* cmovo */
-			d |= (_eflags & EFLG_OF) ? Mov : 0;
+			no_wb &= (_eflags & EFLG_OF) ? 0 : 1;
 			break;
 		case 1:	/* cmovb/cmovc/cmovnae */
-			d |= (_eflags & EFLG_CF) ? Mov : 0;
+			no_wb &= (_eflags & EFLG_CF) ? 0 : 1;
 			break;
 		case 2:	/* cmovz/cmove */
-			d |= (_eflags & EFLG_ZF) ? Mov : 0;
+			no_wb &= (_eflags & EFLG_ZF) ? 0 : 1;
 			break;
 		case 3:	/* cmovbe/cmovna */
-			d |= (_eflags & (EFLG_CF | EFLG_ZF)) ? Mov : 0;
+			no_wb &= (_eflags & (EFLG_CF | EFLG_ZF)) ? 0 : 1;
 			break;
 		case 4:	/* cmovs */
-			d |= (_eflags & EFLG_SF) ? Mov : 0;
+			no_wb &= (_eflags & EFLG_SF) ? 0 : 1;
 			break;
 		case 5:	/* cmovp/cmovpe */
-			d |= (_eflags & EFLG_PF) ? Mov : 0;
+			no_wb &= (_eflags & EFLG_PF) ? 0 : 1;
 			break;
 		case 7:	/* cmovle/cmovng */
-			d |= (_eflags & EFLG_ZF) ? Mov : 0;
+			no_wb &= (_eflags & EFLG_ZF) ? 0 : 1;
 			/* fall through */
 		case 6:	/* cmovl/cmovnge */
-			d |= (!(_eflags & EFLG_SF) !=
-			      !(_eflags & EFLG_OF)) ? Mov : 0;
+			no_wb &= (!(_eflags & EFLG_SF) !=
+			      !(_eflags & EFLG_OF)) ? 0 : 1;
 			break;
 		}
 		/* Odd cmov opcodes (lsb == 1) have inverted sense. */
-		d ^= (b & 1) ? Mov : 0;
+		no_wb ^= (b & 1) ? 1 : 0;
 		break;
 	case 0xb0 ... 0xb1:	/* cmpxchg */
 		/*

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