[PATCH] KVM: Fix lockup on 32-bit intel hosts with nx disabled in the bios

[PATCH] KVM: Fix lockup on 32-bit intel hosts with nx disabled in the bios

[Avi Kivity]

Intel hosts, without long mode, and with nx support disabled in the bios
have an efer that is readable but not writable.  This causes a lockup on
switch to guest mode (even though it should exit with reason 34 according to
the documentation).

Signed-off-by: Avi Kivity <avi@qumranet.com>

Index: linux-2.6/drivers/kvm/vmx.c
===================================================================
--- linux-2.6.orig/drivers/kvm/vmx.c
+++ linux-2.6/drivers/kvm/vmx.c
@@ -1128,6 +1128,8 @@ static int vmx_vcpu_setup(struct kvm_vcp
 
 		if (rdmsr_safe(index, &data_low, &data_high) < 0)
 			continue;
+		if (wrmsr_safe(index, data_low, data_high) < 0)
+			continue;
 		data = data_low | ((u64)data_high << 32);
 		vcpu->host_msrs[j].index = index;
 		vcpu->host_msrs[j].reserved = 0;

Re: [PATCH] KVM: Fix lockup on 32-bit intel hosts with nx disabled in the bios

[Avi Kivity]

Avi Kivity wrote:
> Intel hosts, without long mode, and with nx support disabled in the bios
> have an efer that is readable but not writable.  This causes a lockup on
> switch to guest mode (even though it should exit with reason 34 according to
> the documentation).
>
>   

Andrew, I believe this is 2.6.20 material.

> Signed-off-by: Avi Kivity <avi@qumranet.com>
>
> Index: linux-2.6/drivers/kvm/vmx.c
> ===================================================================
> --- linux-2.6.orig/drivers/kvm/vmx.c
> +++ linux-2.6/drivers/kvm/vmx.c
> @@ -1128,6 +1128,8 @@ static int vmx_vcpu_setup(struct kvm_vcp
>  
>  		if (rdmsr_safe(index, &data_low, &data_high) < 0)
>  			continue;
> +		if (wrmsr_safe(index, data_low, data_high) < 0)
> +			continue;
>  		data = data_low | ((u64)data_high << 32);
>  		vcpu->host_msrs[j].index = index;
>  		vcpu->host_msrs[j].reserved = 0;
>   


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

Re: [kvm-devel] [PATCH] KVM: Fix lockup on 32-bit intel hosts with nx disabled in the bios

[Jeff Chua]

On 1/31/07, Avi Kivity <avi@qumranet.com> wrote:
> Intel hosts, without long mode, and with nx support disabled in the bios
> have an efer that is readable but not writable.  This causes a lockup on
> switch to guest mode (even though it should exit with reason 34 according to
> the documentation).

Avi, thank you for the patch. I can confirm that this patch works on
my IBM X60s notebook. Without it, the whole PC locks up upon starting
qemu.

Thanks,
Jeff.

Re: [PATCH] KVM: Fix lockup on 32-bit intel hosts with nx disabled in the bios

[Ingo Molnar]

* Avi Kivity <avi@qumranet.com> wrote:

> Intel hosts, without long mode, and with nx support disabled in the 
> bios have an efer that is readable but not writable.  This causes a 
> lockup on switch to guest mode (even though it should exit with reason 
> 34 according to the documentation).
> 
> Signed-off-by: Avi Kivity <avi@qumranet.com>

i think this is for v2.6.20. I have tested this ontop of -rc7.

Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo