> -----Original Message----- > From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > Sent: Wednesday, January 30, 2013 3:53 AM > To: KY Srinivasan > Cc: olaf@xxxxxxxxx; bp@xxxxxxxxx; apw@xxxxxxxxxxxxx; x86@xxxxxxxxxx; > tglx@xxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; > jasowang@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; hpa@xxxxxxxxx > Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V > > >>> On 30.01.13 at 01:51, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> wrote: > > Xen emulates Hyper-V to host enlightened Windows. Looks like this > > emulation may be turned on by default even for Linux guests. Check and > > fail Hyper-V detection if we are on Xen. > > > > Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx> > > --- > > arch/x86/kernel/cpu/mshyperv.c | 7 +++++++ > > 1 files changed, 7 insertions(+), 0 deletions(-) > > > > diff --git a/arch/x86/kernel/cpu/mshyperv.c > b/arch/x86/kernel/cpu/mshyperv.c > > index 646d192..4dab317 100644 > > --- a/arch/x86/kernel/cpu/mshyperv.c > > +++ b/arch/x86/kernel/cpu/mshyperv.c > > @@ -30,6 +30,13 @@ static bool __init ms_hyperv_platform(void) > > if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) > > return false; > > > > + /* > > + * Xen emulates Hyper-V to support enlightened Windows. > > + * Check to see first if we are on a Xen Hypervisor. > > + */ > > + if (xen_cpuid_base()) > > + return false; > > + > > cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS, > > &eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]); > > I'm not convinced that's the right approach - any hypervisor > could do similar emulation, and hence you either want to make > sure you run on Hyper-V (by excluding all others), or you > tolerate using the emulation (which may require syncing up with > the other guest implementations so that shared resources don't > get used by two parties). > > I also wonder whether using the Hyper-V emulation (where > useful, there might not be anything right now, but this may > change going forward) when no Xen support is configured > wouldn't be better than not using anything... Jan, Presumably, Hyper-V emulation is only to run enlightened Windows. The issue with Xen is not that it emulates Hyper-V, but this emulation is turned on while running Linux. That is the reason I chose to check for Xen. Would you prefer a DMI check for the Hyper-V platform. Regards, K. Y _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
