From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [PATCH RFC] pvh: clearly specify used parameters in vcpu_guest_context Date: Mon, 18 Nov 2013 11:50:51 +0000 Message-ID: <5289FF1B.1080709@eu.citrix.com> References: <1384530622-31703-1-git-send-email-roger.pau@citrix.com> <52865AC60200007800103AAE@nat28.tlf.novell.com> <52864E97.9020402@eu.citrix.com> <52865DCB0200007800103AD8@nat28.tlf.novell.com> <20131115135654.52e52bd4@mantra.us.oracle.com> <20131115155652.3201414a@mantra.us.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1ViNM7-0007Uk-29 for xen-devel@lists.xenproject.org; Mon, 18 Nov 2013 11:51:03 +0000 In-Reply-To: <20131115155652.3201414a@mantra.us.oracle.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: Mukesh Rathor Cc: Keir Fraser , Tim Deegan , Jan Beulich , xen-devel@lists.xenproject.org, Roger Pau Monne List-Id: xen-devel@lists.xenproject.org On 15/11/13 23:56, Mukesh Rathor wrote: > On Fri, 15 Nov 2013 13:56:54 -0800 > Mukesh Rathor wrote: > >> On Fri, 15 Nov 2013 16:45:47 +0000 >> "Jan Beulich" wrote: >> >>>>>> On 15.11.13 at 17:40, George Dunlap >>>>>> wrote: >>>> On 15/11/13 16:32, Jan Beulich wrote: >>>>>>>> On 15.11.13 at 16:50, Roger Pau Monne >>>>>>>> wrote: >>>>>> --- a/xen/arch/x86/domain.c >>>>>> +++ b/xen/arch/x86/domain.c >>>>>> @@ -704,9 +704,11 @@ int arch_set_info_guest( >>>>>> /* PVH 32bitfixme */ >>>>>> ASSERT(!compat); >>>>>> >>>>>> - if ( c(ctrlreg[1]) || c(ldt_base) || c(ldt_ents) || >>>>>> + if ( c(ctrlreg[0]) || c(ctrlreg[1]) || c(ctrlreg[2]) || >>>>>> + c(ctrlreg[4]) || c(ldt_base) || c(ldt_ents) || >>>>> I think it should actually be a bug for the guest to request an >>>>> all blank CR0 or CR4. Minimally CR0.PE, CR0.PG, and CR4.PAE >>>>> would seem to be a valid requirement to be set. >>>>> >>>>> Apart from that ctrlreg[] is an 8-element array... And I don't >>>>> see debugreg[] being verified at all. >>>>> >>>>>> c(user_regs.cs) || c(user_regs.ss) || >>>>>> c(user_regs.es) || c(user_regs.ds) || c(user_regs.fs) || >>>>>> c(user_regs.gs) || >>>>>> + c(kernel_ss) || c(kernel_sp) || >>>>>> c.nat->gs_base_kernel || >>>>> So George and/or Mukesh found it necessary to set >>>>> gs_base_kernel, and you rip it out? I'm curious as to what >>>>> they're going to say... >>>> I didn't find it necessary; I was mostly focused on merging the >>>> PVH and HVM codepaths without causing any regressions. It's not >>>> obvious to me what's special about gs_base_kernel, and I haven't >>>> yet gone back to try to find out why Mukesh did it that way. >> Hi, >> >> We had talked about this while ago, but upon boot, the first thing >> a vcpu needs is access to kernel data structure. (A secondary vcpu >> is bootstrapped way up into the kernel). It would be possible to >> get rid of gs_base_kernel, but will take some work on the linux side. >> I can try and test it out, and let you guys know. > Ok, looking at this more, I can hack cpu_bringup_and_idle() in > linux to include a static variable for cpuid, which is the least a > vcpu needs to know first thing. But, I think that would not work when > vcpu hotplug support is added. Another option would be to pass cpuid > in one of the registers, say rdi. Thus, rdi == cpuid will be passed > to VCPUOP_initialise. In bringup function, the booting vcpu can then > load it's own gs based on the cpuid. If linux folks, konrad (CCd), is OK > with this, we can remove gs_base_kernel. Otherwise, it's such a small > thing, hopefually it can stay. So Linux has the exact same problem on native, and (AFAICT) they solve it by simply writing gs to a global variable called initial_gs. Is there any reason why we can't just do what native Linux does here? We should, in fact, be able to use the exact same variable. -George