From: andrew.cooper3@citrix.com (Andrew Cooper) Date: Mon, 8 Feb 2016 16:05:47 +0000 Subject: [Cocci] [Xen-devel] [PATCH v2 3/3] paravirt: rename paravirt_enabled to paravirt_legacy In-Reply-To: <20160208155507.GF28980@pd.tnic> References: <1454733014-15237-1-git-send-email-mcgrof@kernel.org> <1454733014-15237-4-git-send-email-mcgrof@kernel.org> <20160206085930.GF25240@wotan.suse.de> <20160206220437.GA4435@pd.tnic> <56B8B6BF.6030007@oracle.com> <20160208155507.GF28980@pd.tnic> Message-ID: <56B8BCDB.9040701@citrix.com> To: cocci@systeme.lip6.fr List-Id: cocci@systeme.lip6.fr On 08/02/16 15:55, Borislav Petkov wrote: > On Mon, Feb 08, 2016 at 10:39:43AM -0500, Boris Ostrovsky wrote: >> It does. Very much IIRC, the problem was not caused by an access to MSR but >> rather some sort of address not being available somewhere. > See below. > >>> - microcode application on Xen: we've had this before. The hypervisor >>> should do that (if it doesn't do so already). >> it does. > Good. > >>> So yes, that paravirt_enabled() thing should go away. Even more so if we >>> have CPUID leaf 0x4... reserved for hypervisors. >> I actually think this was the original proposal until we realized we had >> paravirt_enabled(). So we can go back to checking CPUID 0x40000000. >> >> We might also be able to test for (x86_hyper!=NULL) and have guests that do >> microcode management prior to init_hypervisor() rely on hypervisors ignoring >> MSR accesses (as they do today). > Right, so the early loader can't do that as on 32-bit it runs even > before paging has been enabled. So I *think* the thing with CPUID would > be best. What does the xen hypervisor return in regs when I do CPUID(4)? > I.e., how do I reliably detect it in the guest? > > I can whip up a quick patch and get rid of paravirt_enabled() while at > it... > For compatibility with other virtualisation specs, Xen's cpuid leaves shift depending on configuration. Spec at http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/arch-x86/cpuid.h;h=d709340f18d089560b959835eabb7b6609542c7e;hb=HEAD#l33 Basically, they are either at 0x40000000, or 0x40000100 if viridian or vmware compatibility has been enabled. ~Andrew