2016-05-31 13:06+0300, kmeaw@xxxxxxxxxxxxxx: > 31.05.2016, 11:21, "Paolo Bonzini" <pbonzini@xxxxxxxxxx>: > >> 2016-05-27 17:22+0200, Radim Krčmář: > >> > (I wonder why MacOS X doesn't read IA32_PERF_STATUS, though.) > >> > >> Oh, it maybe does ... we already emulate status and return 0x1000 in its > >> bottom 16 bits. I have no idea what is that supposed to mean, but I > >> think we should return 0x1000 in IA32_PERF_CTL then. > > > > It's 1000, not 0x1000 (instead, on real hardware the value is typically a > > multiple of 256). It was added for Darwin too. > > > > Returning different values is okay, because they are different on real > > hardware too: > > > > (sudo dd if=/dev/cpu/0/msr skip=$((0x198)) iflag=skip_bytes bs=8 count=1; > > sudo dd if=/dev/cpu/0/msr skip=$((0x199)) iflag=skip_bytes bs=8 count=1) | od -tx8 > > 0000000 00001f3900001100 0000000000001300 > > ^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ > > PERF_STATUS PERF_CTL > > > > And perhaps if we returned non-zero values for PERF_CTL Darwin would try to > > write to it. So returning zero is fine, I think. There is no correct answer... > > Thank you. I have removed MSR_IA32_PERF_CTL from emulated_msrs[]. Returning > 1000 (0x3e8) for PERF_STATUS and 0 for PERF_CTL works fine with MacOS X. > > Just in case here are MSRs from i5-4460: > PERF_STATUS: 0000202800002100 > PERF_CTL: 0000000000002200 > > Chaning KVM's PERL_CTL from 0 to 0x2200 does not seem to interfere with MacOS X > boot process. It does not attempt to wrmsr into this register. > > Here is a refined version of the patch: > -- > > From: Dmitry Bilunov <kmeaw@xxxxxxxxxxxxxx> > > Intel CPUs having Turbo Boost feature implement an MSR to provide a > control interface via rdmsr/wrmsr instructions. One could detect the > presence of this feature by issuing one of these instructions and > handling the #GP exception which is generated in case the referenced MSR > is not implemented by the CPU. > > KVM's vCPU model behaves exactly as a real CPU in this case by injecting > a fault when MSR_IA32_PERF_CTL is called (which KVM does not support). > However, some operating systems use this register during an early boot > stage in which their kernel is not capable of handling #GP correctly, > causing #DP and finally a triple fault effectively resetting the vCPU. > > This patch implements a dummy handler for MSR_IA32_PERF_CTL to avoid the > crashes. > --- The code looks good. Please resend with your signed-off-by and preserved writespace (tabs were converted to spaces), thanks. > arch/x86/kvm/x86.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c805cf4..d0a5b4b 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2314,6 +2314,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > case MSR_AMD64_NB_CFG: > case MSR_FAM10H_MMIO_CONF_BASE: > case MSR_AMD64_BU_CFG2: > + case MSR_IA32_PERF_CTL: > msr_info->data = 0; > break; > case MSR_K7_EVNTSEL0 ... MSR_K7_EVNTSEL3: > -- > 2.8.2 -- 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
