On 12/25/2011 08:39 PM, Jan Kiszka wrote: > On 2011-12-25 14:03, Avi Kivity wrote: > > From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > > > > Unlike all of the other cpuid bits, the TSC deadline timer bit is set > > unconditionally, regardless of what userspace wants. > > > > This is broken in several ways: > > - if userspace doesn't use KVM_CREATE_IRQCHIP, and doesn't emulate the TSC > > deadline timer feature, a guest that uses the feature will break > > - live migration to older host kernels that don't support the TSC deadline > > timer will cause the feature to be pulled from under the guest's feet; > > breaking it > > - guests that are broken wrt the feature will fail. > > > > Fix by not enabling the feature automatically; instead report it to userspace. > > Because the feature depends on KVM_CREATE_IRQCHIP, which we cannot guarantee > > will be called, we expose it via a KVM_CAP_TSC_DEADLINE_TIMER and not > > KVM_GET_SUPPORTED_CPUID. > > > > Fixes the Illumos guest kernel, which uses the TSC deadline timer feature. > > > > [avi: add the KVM_CAP + documentation] > > > > Reported-by: Alexey Zaytsev <alexey.zaytsev@xxxxxxxxx> > > Signed-off-by: Avi Kivity <avi@xxxxxxxxxx> > > --- > > > > As we're running out of time and everyone's checking their socks instead of > > inboxes I've added the missing parts myself. Jan, if you accidentally see > > this, please review and add your signoff. > > I'm sorry for not holding my promise, was distracted the past days. > Patch looks good to me, just some minor phrasing corrections below. Not a problem at all, I can guess you had much better things to do. > > Signed-off-by; Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > > > > > Documentation/virtual/kvm/api.txt | 9 +++++++++ > > arch/x86/kvm/cpuid.c | 16 ++++++---------- > > arch/x86/kvm/x86.c | 3 +++ > > include/linux/kvm.h | 1 + > > 4 files changed, 19 insertions(+), 10 deletions(-) > > > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > > index 5b03eee..da1f8fd 100644 > > --- a/Documentation/virtual/kvm/api.txt > > +++ b/Documentation/virtual/kvm/api.txt > > @@ -1100,6 +1100,15 @@ emulate them efficiently. The fields in each entry are defined as follows: > > eax, ebx, ecx, edx: the values returned by the cpuid instruction for > > this function/index combination > > > > +The TSC deadline timer feature (CPUID leaf 1, ecx[24]) is always returned > > +as false, since the feature depends on KVM_CREATE_IRQCHIP for local APIC > > +support. Instead it is reported via > > + > > + ioctl(KVM_CHECK_EXTENSION, KVM_CAP_TSC_DEADLINE_TIMER) > > + > > +if that returns true you use KVM_CREATE_IRQCHIP, or if emulate the > ^^^ ^^^ > and you > Thanks, added your signoff and adjusted this. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
