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Date: Fri, 28 Mar 2008 09:59:32 -0300
From: Glauber Costa <gcosta@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] ignore reads to the EOI register.
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: kvm-devel@lists.sourceforge.net, glommer@gmail.com, qemu-devel@nongnu.org, macro@linux-mips.org

Aurelien Jarno wrote:
> On Wed, Mar 26, 2008 at 09:57:16PM -0300, Glauber Costa wrote:
>> They seem legal in real hardware, even though the EOI
>> is a write-only register. By "legal" I mean they are completely
>> ignored, but at least, don't cause any bits to be set at ESR.
>>
>> Without this patch, some (very recent) linux git trees will fail
>> to boot in i386.
>>
>> This is generated from kvm-userspace, but should apply well to
>> plain qemu too.
>>
>> Signed-off-by: Glauber Costa <gcosta@redhat.com>
>> ---
>>  qemu/hw/apic.c |    2 ++
>>  1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/qemu/hw/apic.c b/qemu/hw/apic.c
>> index 92248dd..4102493 100644
>> --- a/qemu/hw/apic.c
>> +++ b/qemu/hw/apic.c
>> @@ -615,6 +615,8 @@ static uint32_t apic_mem_readl(void *opaque, target_phys_addr_t addr)
>>          /* ppr */
>>          val = apic_get_ppr(s);
>>          break;
>> +    case 0x0b:
>> +        break;
> 
> While I agree the guest should not care of the value (it should actually
> not read it), wouldn't it be safer to return a default value (0 ?) 
> instead of an initialized value?
> 
I don't think it would really make any difference, but is not opposed to 
this solution either.