From 435beb84b5092d304c5ccd343b445010d5a38a4e Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Mon, 11 May 2015 10:42:35 +0200 Subject: [PATCH] x86/hvm: permit HVM_PARAM_IDENT_PT to be set more than once There is no conceptual problem with setting this parameter more than once. Checkpointed migration streams will typically set it once per checkpoint to the same value. The parameter is only actually needed on early-generation VT-x which lacked the unrestricted guest capability, although it could plausibly be used on newer VT-x with unusual execution control settings. Short circuit the expensive operations on non VT-x hardware. The parameter itself must always be latched to avoid issues if the VM eventually migrates to a host which needs to use the pagetable. Signed-off-by: Andrew Cooper --- xen/arch/x86/hvm/hvm.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 78b0efb8bf..689e402e0f 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -5712,13 +5712,15 @@ static int hvmop_set_param( rc = -EINVAL; break; case HVM_PARAM_IDENT_PT: - rc = -EINVAL; - if ( d->arch.hvm_domain.params[a.index] != 0 ) - break; - - rc = 0; - if ( !paging_mode_hap(d) ) + /* + * Only actually required for VT-x lacking unrestricted_guest + * capabilities. Short circuit the pause if possible. + */ + if ( !paging_mode_hap(d) || !cpu_has_vmx ) + { + d->arch.hvm_domain.params[a.index] = a.value; break; + } /* * Update GUEST_CR3 in each VMCS to point at identity map. -- 2.30.2