On Tue, Mar 14, 2017 at 02:58:24PM +0100, Radim Krčmář wrote: > 2017-03-14 01:44+0200, Michael S. Tsirkin: > > Guests running Mac OS 5, 6, and 7 (Leopard through Lion) have a problem: > > unless explicitly provided with kernel command line argument > > "idlehalt=0" they'd implicitly assume MONITOR and MWAIT availability, > > without checking CPUID. > > > > We currently emulate that as a NOP but on VMX we can do better: let > > guest stop the CPU until timer, IPI or memory change. CPU will be busy > > but that isn't any worse than a NOP emulation. > > > > Note that mwait within guests is not the same as on real hardware > > because halt causes an exit while mwait doesn't. For this reason it > > might not be a good idea to use the regular MWAIT flag in CPUID to > > signal this capability. Add a flag in the hypervisor leaf instead. > > > > Additionally, we add a capability for QEMU - e.g. if it knows there's an > > isolated CPU dedicated for the VCPU it can set the standard MWAIT flag > > to improve guest behaviour. > > > > Reported-by: "Gabriel L. Somlo" <gsomlo@xxxxxxxxx> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > --- > > > > Note: SVM bits are untested at this point. Seems pretty > > obvious though. > > > > changes from v2: > > - add a capability to allow host userspace to detect new kernels > > - more documentation to clarify the semantics of the feature flag > > and why it's useful > > - svm support as suggested by Radim > > > > changes from v1: > > - typo fix resulting in rest of leaf flags being overwritten > > Reported by: Wanpeng Li <kernellwp@xxxxxxxxx> > > - updated commit log with data about guests helped by this feature > > - better document differences between mwait and halt for guests > > > > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > > @@ -4135,11 +4135,11 @@ available, means that that the kernel can support guests using the > > radix MMU defined in Power ISA V3.00 (as implemented in the POWER9 > > processor). > > > > -8.4 KVM_CAP_PPC_HASH_MMU_V3 > > This patch should not not remove the PPC capability from docs. > > (The right name is KVM_CAP_PPC_HASH_V3, but that is for another patch.) Oops my bad. If you do decide you want me to respin because of this, pls let me know. > > +8.5 KVM_CAP_X86_GUEST_MWAIT > > > > -Architectures: ppc > > +Architectures: x86 > > > > -This capability, if KVM_CHECK_EXTENSION indicates that it is > > -available, means that that the kernel can support guests using the > > -hashed page table MMU defined in Power ISA V3.00 (as implemented in > > -the POWER9 processor), including in-memory segment tables. > > +This capability indicates that guest using memory monotoring instructions > > +(MWAIT/MWAITX) to stop the virtual CPU will not cause a VM exit. As such time > > +spent while virtual CPU is halted in this way will then be accounted for as > > +guest running time on the host (as opposed to e.g. HLT). > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > @@ -2684,6 +2684,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > > case KVM_CAP_ADJUST_CLOCK: > > r = KVM_CLOCK_TSC_STABLE; > > break; > > + case KVM_CAP_X86_GUEST_MWAIT: > > + r = !!this_cpu_has(X86_FEATURE_MWAIT); > > this_cpu_has already returns bool, so !! is not needed. > > I can fix both while applying. OK, pls let me know if you need any more. > > + break; > > case KVM_CAP_X86_SMM: > > /* SMBASE is usually relocated above 1M on modern chipsets, > > * and SMM handlers might indeed rely on 4G segment limits, -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
