Re: [PATCH v2 02/13] nestedsvm: Adjust L2's DR intercept when adjusting L1

[Jan Beulich <jbeulich@suse.com>]

On 10.10.2026 12:13, chunjie.zhu@citrix.com wrote:
> From: Ross Lagerwall <ross.lagerwall@citrix.com>
> 
> If L2 accesses a debug register (like reading DR7) without L1 intercepting
> it, it locks up the vCPU. L0 intercepts VMEXIT_DR7_READ, which disables
> the intercept for L1 and then restarts L2 which re-executes the
> instruction and then this repeats indefinitely.
> 
> Disable the intercept for the current VMCB if in guest mode to reflect
> what would happen if the VMCB were recreated via
> nsvm_vmcb_prepare4vmrun().
> 
> Fixes: a59a7be91b61 ("nestedsvm: fix DRn handling")
> Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>

Andrew's comment [1] was left unaddressed. Comments on earlier versions
should be dealt with, one way or another, before re-submitting.

Jan

> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -1657,6 +1657,8 @@ static void svm_dr_access(struct vcpu *v, struct cpu_user_regs *regs)
>  
>      TRACE(TRC_HVM_DR_WRITE);
>      __restore_debug_registers(vmcb, v);
> +    if ( nestedhvm_enabled(v->domain) && nestedhvm_vcpu_in_guestmode(v) )
> +        vmcb_set_dr_intercepts(v->arch.hvm.svm.vmcb, 0);
>  }
>  
>  static int cf_check svm_msr_read_intercept(