From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: Should hvm_hw_cpu's sysenter_eip always be zero after xc_domain_hvm_getcontext_partial()? Date: Fri, 31 Jul 2015 16:13:24 +0100 Message-ID: <55BB9094.30703@citrix.com> References: <55BB8D9A.2070705@bitdefender.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55BB8D9A.2070705@bitdefender.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Razvan Cojocaru , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 31/07/15 16:00, Razvan Cojocaru wrote: > Hello, > > It has become apparent that after a succesful > xc_domain_hvm_getcontext_partial( ..., HVM_SAVE_CODE(CPU), ...) call, > the sysenter_eip member of struct hvm_hw_cpu is always zero. How odd. > > Looking in the code, the only two __vmwrite(GUEST_SYSENTER_EIP, ...) > calls occur in xen/arch/x86/hvm/vmx/vmx.c. One is in > vmx_msr_write_intercept(), but adding a printk() just after produces no > output after starting and stopping a guest. Write interception for that MSR is disabled (if the hardware supports disabling interception) because it is not interesting. You can re-enable interception by commenting out the appropriate vmx_disable_intercept_for_msr() line in construct_vmcs() > > The other is in vmx_vmcs_restore(), which seems to dutifully restore the > never-set value of zero after a save. > > So this doesn't seem to be actually initialized anywhere. Could somebody > please recommend the best place to initialize it, and the best value to > initialize it with? Or maybe you could point out what I'm missing, if > that's the case? Are you certain that the guest is actually setting it? If the guest never sets it in the first place, 0 will be the expected value. ~Andrew