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

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

[Orit Wasserman]

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;
+		}
+	}
 }
 
 static void vmx_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)
-- 
1.7.7.6

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

[Avi Kivity]

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