Re: [Xen-devel] [PATCH 04/11] x86: Fix calculation of %dr6/7 reserved bits

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jun 04, 2018 at 02:59:08PM +0100, Andrew Cooper wrote:
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 10415e6..7fddae1 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -977,6 +977,7 @@ unsigned long hvm_cr4_guest_valid_bits(const struct 
> domain *d, bool restore)
>  
>  static int hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
>  {
> +    const struct cpuid_policy *cp = d->arch.cpuid;
>      int vcpuid;
>      struct vcpu *v;
>      struct hvm_hw_cpu ctxt;
> @@ -1154,8 +1155,8 @@ static int hvm_load_cpu_ctxt(struct domain *d, 
> hvm_domain_context_t *h)
>      v->arch.debugreg[1] = ctxt.dr1;
>      v->arch.debugreg[2] = ctxt.dr2;
>      v->arch.debugreg[3] = ctxt.dr3;
> -    v->arch.debugreg[6] = ctxt.dr6;
> -    v->arch.debugreg[7] = ctxt.dr7;
> +    v->arch.debugreg[6] = adjust_dr6_rsvd(ctxt.dr6, cp->feat.rtm);
> +    v->arch.debugreg[7] = adjust_dr7_rsvd(ctxt.dr7, cp->feat.rtm);

I don't know much, but if the value in dr6/dr7 is changed from the one
in the provided context, won't the guest experience issues?

Won't it be better to plain refuse to load a context that has
unsupported DR6/7 values?

Thanks, Roger.

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