"Dr. David Alan Gilbert" <dgilb...@redhat.com> writes: > * Vitaly Kuznetsov (vkuzn...@redhat.com) wrote: >> "Dr. David Alan Gilbert" <dgilb...@redhat.com> writes: >> >> > * Vitaly Kuznetsov (vkuzn...@redhat.com) wrote: >> >> KVM doesn't fully support Hyper-V reenlightenment notifications on >> >> migration. In particular, it doesn't support emulating TSC frequency >> >> of the source host by trapping all TSC accesses so unless TSC scaling >> >> is supported on the destination host and KVM_SET_TSC_KHZ succeeds, it >> >> is unsafe to proceed with migration. >> >> >> >> KVM_SET_TSC_KHZ is called from two sites: kvm_arch_init_vcpu() and >> >> kvm_arch_put_registers(). The later (intentionally) doesn't propagate >> >> errors allowing migrations to succeed even when TSC scaling is not >> >> supported on the destination. This doesn't suit 're-enlightenment' >> >> use-case as we have to guarantee that TSC frequency stays constant. >> >> >> >> Require 'tsc-frequency=' command line option to be specified for >> >> successful >> >> migration when re-enlightenment was enabled by the guest. >> >> >> >> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com> >> >> --- >> >> This patch is a successor of "[PATCH 3/3] i386: Make sure >> >> kvm_arch_set_tsc_khz() succeeds on migration when 'hv-reenlightenment' >> >> was exposed" taking a different approach suggested by Paolo. >> >> --- >> >> docs/hyperv.txt | 5 +++++ >> >> target/i386/kvm/hyperv-proto.h | 1 + >> >> target/i386/machine.c | 20 ++++++++++++++++++++ >> >> 3 files changed, 26 insertions(+) >> >> >> >> diff --git a/docs/hyperv.txt b/docs/hyperv.txt >> >> index 5df00da54fc4..e53c581f4586 100644 >> >> --- a/docs/hyperv.txt >> >> +++ b/docs/hyperv.txt >> >> @@ -160,6 +160,11 @@ the hypervisor) until it is ready to switch to the >> >> new one. This, in conjunction >> >> with hv-frequencies, allows Hyper-V on KVM to pass stable clocksource >> >> (Reference >> >> TSC page) to its own guests. >> >> >> >> +Note, KVM doesn't fully support re-enlightenment notifications and >> >> doesn't >> >> +emulate TSC accesses after migration so 'tsc-frequency=' CPU option also >> >> has to >> >> +be specified to make migration succeed. The destination host has to >> >> either have >> >> +the same TSC frequency or support TSC scaling CPU feature. >> >> + >> >> Recommended: hv-frequencies >> >> >> >> 3.16. hv-evmcs >> >> diff --git a/target/i386/kvm/hyperv-proto.h >> >> b/target/i386/kvm/hyperv-proto.h >> >> index 056a305be38c..e30d64b4ade4 100644 >> >> --- a/target/i386/kvm/hyperv-proto.h >> >> +++ b/target/i386/kvm/hyperv-proto.h >> >> @@ -139,6 +139,7 @@ >> >> * Reenlightenment notification MSRs >> >> */ >> >> #define HV_X64_MSR_REENLIGHTENMENT_CONTROL 0x40000106 >> >> +#define HV_REENLIGHTENMENT_ENABLE_BIT (1u << 16) >> >> #define HV_X64_MSR_TSC_EMULATION_CONTROL 0x40000107 >> >> #define HV_X64_MSR_TSC_EMULATION_STATUS 0x40000108 >> >> >> >> diff --git a/target/i386/machine.c b/target/i386/machine.c >> >> index 7259fe6868c6..137604ddb898 100644 >> >> --- a/target/i386/machine.c >> >> +++ b/target/i386/machine.c >> >> @@ -883,11 +883,31 @@ static bool >> >> hyperv_reenlightenment_enable_needed(void *opaque) >> >> env->msr_hv_tsc_emulation_status != 0; >> >> } >> >> >> >> +static int hyperv_reenlightenment_post_load(void *opaque, int version_id) >> >> +{ >> >> + X86CPU *cpu = opaque; >> >> + CPUX86State *env = &cpu->env; >> >> + >> >> + /* >> >> + * KVM doesn't fully support re-enlightenment notifications so we >> >> need to >> >> + * make sure TSC frequency doesn't change upon migration. >> >> + */ >> >> + if ((env->msr_hv_reenlightenment_control & >> >> HV_REENLIGHTENMENT_ENABLE_BIT) && >> >> + !env->user_tsc_khz) { >> >> + error_report("Guest enabled re-enlightenment notifications, " >> >> + "'tsc-frequency=' has to be specified"); >> > >> > It's unusual to fail on the destination for a valid configuration but >> > guest state; wouldn't it be better to always insist on tsc-frequency if >> > that hv feature is exposed; failing early before reeiving the state? >> > >> >> Doing so would make a number of currently existing configurations >> invalid, even when re-enlightenment is not to be used by the >> guest. AFAIR Windows without Hyper-V doesn't enable it. Generally, we >> just advise people to 'enable all currently supported hyper-v >> enlightenments' to make things easier so reenlightenment may end up >> being added for no particular reason. > > Ouch, that's difficult - the problem with testing this late is that the > migration fails right at the end so it's an unpleasent surprise. > > Could you disallow re-enlightenment without tsc-frequency on new machine > types? >
Will do. I'm not exactly sure if I should target 6.0 or 6.1 atm, let's try the former first. -- Vitaly