Re: [patch 3/3] KVM: VMX: handle segment limit granularity special case in software

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
> As the comment in the diff mentions, VMX does not accept any bit in
> the range 11:0 of ES,CS,FS,GS,SS segment registers limit field to 
> be zero with the granulity bit set to one.
>
> So clear granularity and adjust the limit accordingly. 
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Index: kvm/arch/x86/kvm/vmx.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/vmx.c
> +++ kvm/arch/x86/kvm/vmx.c
> @@ -1665,6 +1665,22 @@ static void vmx_set_segment(struct kvm_v
>  		return;
>  	}
>  	vmcs_writel(sf->base, var->base);
> +
> +	/*
> + 	 * section 22.3.1.2:
> + 	 * - If any bit in the limit field in the range 11:0 is 0, G must be 0.
> + 	 * - If any bit in the limit field in the range 31:20 is 1, G must be 1.
> + 	 */
> +	if (!vcpu->arch.rmode.active && !var->unusable &&
> +	     seg != VCPU_SREG_TR && seg != VCPU_SREG_LDTR) {
> +#define SEG_MASK ((1 << 12)-1)
> +		if (var->g && (var->limit & SEG_MASK) != SEG_MASK) {
> +			var->g = 0;
> +			var->limit <<= 12;
> +			var->limit |= SEG_MASK;
> +		}
> +	}
> +

Both kvm_segment::limit and vmx's GUEST_xS_LIMIT are normalized (always 
in bytes), so I don't see why you are modifying var->limit (which is an 
input parameter!)


-- 
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