Re: [PATCH] Fix migration of real mode guests from host with unrestricted guest to a host without it.

[Avi Kivity <avi@redhat.com>]

On 05/31/2012 02:13 PM, Orit Wasserman wrote:
> For example migration between Westmere and Nehelem hosts.
> The patch fixes the guest segments similar to enter_rmode function.
> 
> Signed-off-by: Orit Wasserman <owasserm@rehdat.com>
> ---
>  arch/x86/kvm/vmx.c |   38 ++++++++++++++++++++++++++++++++++++++
>  1 files changed, 38 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 32eb588..2eca18f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3229,6 +3229,44 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu,
>  
>  	vmcs_write32(sf->ar_bytes, ar);
>  	__clear_bit(VCPU_EXREG_CPL, (ulong *)&vcpu->arch.regs_avail);
> +
> +	/*
> +	 * Fix segments for real mode guest in hosts that don't have
> +	 * "unrestricted_mode" or it was disabled.
> +	 * This is done to allow migration of the guests from hosts with
> +	 * unrestricted guest like Westmere to older host that don't have
> +	 * unrestricted guest like Nehelem.
> +	 */
> +	if (!enable_unrestricted_guest && vmx->rmode.vm86_active) {
> +		switch (seg) {
> +		case VCPU_SREG_CS:
> +			vmcs_write32(GUEST_CS_AR_BYTES, 0xf3);
> +			vmcs_write32(GUEST_CS_LIMIT, 0xffff);
> +			if (vmcs_readl(GUEST_CS_BASE) == 0xffff0000)
> +				vmcs_writel(GUEST_CS_BASE, 0xf0000);
> +			vmcs_write16(GUEST_CS_SELECTOR,
> +				     vmcs_readl(GUEST_CS_BASE) >> 4);
> +			break;
> +		case VCPU_SREG_ES:
> +			fix_rmode_seg(VCPU_SREG_ES, &vmx->rmode.es);
> +			break;
> +		case VCPU_SREG_DS:
> +			fix_rmode_seg(VCPU_SREG_DS, &vmx->rmode.ds);
> +			break;
> +		case VCPU_SREG_GS:
> +			fix_rmode_seg(VCPU_SREG_GS, &vmx->rmode.gs);
> +			break;
> +		case VCPU_SREG_FS:
> +			fix_rmode_seg(VCPU_SREG_FS, &vmx->rmode.fs);
> +			break;
> +		case VCPU_SREG_SS:
> +			vmcs_write16(GUEST_SS_SELECTOR,
> +				     vmcs_readl(GUEST_SS_BASE) >> 4);
> +			vmcs_write32(GUEST_SS_LIMIT, 0xffff);
> +			vmcs_write32(GUEST_SS_AR_BYTES, 0xf3);
> +			break;
> +		}
> +	}
>  }
>  

This duplicates the code in enter_rmode().  Please change enter_rmode()
to vmx_set_segment(vmx_get_segment()) to avoid duplication.

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