Re: [PATCH] KVM: x86 emulator: fix xchg instruction emulation

[Gleb Natapov <gleb@redhat.com>]

On Wed, Jul 14, 2010 at 01:15:09PM +0800, Wei Yongjun wrote:
> If the destination is a memory operand and the memory
> cannot map to a valid page, the xchg instruction emulation
> will fail. If so, we should emulate exchange as write
> to fix it.
> 
> Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Acked-by: Gleb Natapov <gleb@redhat.com>

Without this patch locked instruction does not work on io regions.
They don't just fail, they stuck in endless loop.

> ---
>  arch/x86/kvm/x86.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d94811e..ac63f6f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3560,6 +3560,8 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
>  		goto emul_write;
>  
>  	page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
> +	if (is_error_page(page))
> +		goto emul_write;
>  
>  	kaddr = kmap_atomic(page, KM_USER0);
>  	kaddr += offset_in_page(gpa);
> -- 
> 1.7.0.4
> 
> 
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--
			Gleb.