linux-kernel - Re: [PATCH v2] KVM: IOAPIC: only access APIC registers one dword at a time

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Date:	Fri, 2 Jul 2010 14:42:43 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Jin Dongming <jin.dongming@...css.fujitsu.com>
Subject: Re: [PATCH v2] KVM: IOAPIC: only access APIC registers one dword at
 a time

On Fri, Jul 02, 2010 at 04:00:12PM +0800, Xiao Guangrong wrote:
> The IOAPIC spec says:
> 
> When accessing these registers, accesses must be done one dword at a time.
> For example, software should never access byte 2 from the Data register before
> accessing bytes 0 and 1. The hardware will not attempt to recover from a bad
> programming model in this case.
> 
> So, this patch removes other width access
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  virt/kvm/ioapic.c |   20 +++++++-------------
>  1 files changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> index 1149c60..6610d11 100644
> --- a/virt/kvm/ioapic.c
> +++ b/virt/kvm/ioapic.c
> @@ -288,6 +288,11 @@ static int ioapic_mmio_read(struct kvm_io_device *this, gpa_t addr, int len,
>  	ioapic_debug("addr %lx\n", (unsigned long)addr);
>  	ASSERT(!(addr & 0xf));	/* check alignment */
>  
> +	if (len != 4) {
> +		printk(KERN_WARNING "ioapic: wrong length %d\n", len);
> +		return 0;
> +	}
> +

Just remove the printks please, as guests can flood hosts dmesg.

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