Re: [RFC PATCH v4 14/36] i386/tdx: Implement user specified tsc frequency

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

On 5/13/2022 2:04 AM, Isaku Yamahata wrote:
> On Thu, May 12, 2022 at 11:17:41AM +0800,
> Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
>
> > Reuse "-cpu,tsc-frequency=" to get user wanted tsc frequency and pass it
> > to KVM_TDX_INIT_VM.
> >
> > Besides, sanity check the tsc frequency to be in the legal range and
> > legal granularity (required by TDX module).
>
> Just to make it sure.
> You didn't use VM-scoped KVM_SET_TSC_KHZ because KVM side patch is still in
> kvm/queue?  Once the patch lands, we should use it.

I didn't use VM-scoped KVM_SET_TSC_KHZ is because

1) corresponding TDX KVM v6 series still provides tsc_khz in
   struct kvm_tdx_init_vm

2) Use KVM_SET_TSC_KHZ to set VM-scoped TSC seems possible to be applied 
to all VMs, not limited to TDs. It doesn't look like a small task.

I need more time to evaluate the efforts.

> Thanks,
>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > ---
> >   target/i386/kvm/kvm.c |  8 ++++++++
> >   target/i386/kvm/tdx.c | 18 ++++++++++++++++++
> >   2 files changed, 26 insertions(+)
> >
> > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> > index f2d7c3cf59ac..c51125ab200f 100644
> > --- a/target/i386/kvm/kvm.c
> > +++ b/target/i386/kvm/kvm.c
> > @@ -818,6 +818,14 @@ static int kvm_arch_set_tsc_khz(CPUState *cs)
> >       int r, cur_freq;
> >       bool set_ioctl = false;
> >   
> > +    /*
> > +     * TD guest's TSC is immutable, it cannot be set/changed via
> > +     * KVM_SET_TSC_KHZ, but only be initialized via KVM_TDX_INIT_VM
> > +     */
> > +    if (is_tdx_vm()) {
> > +        return 0;
> > +    }
> > +
> >       if (!env->tsc_khz) {
> >           return 0;
> >       }
> > diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> > index 9f2cdf640b5c..622efc409438 100644
> > --- a/target/i386/kvm/tdx.c
> > +++ b/target/i386/kvm/tdx.c
> > @@ -35,6 +35,9 @@
> >   #define TDX_TD_ATTRIBUTES_PKS               BIT_ULL(30)
> >   #define TDX_TD_ATTRIBUTES_PERFMON           BIT_ULL(63)
> >   
> > +#define TDX_MIN_TSC_FREQUENCY_KHZ   (100 * 1000)
> > +#define TDX_MAX_TSC_FREQUENCY_KHZ   (10 * 1000 * 1000)
> > +
> >   static TdxGuest *tdx_guest;
> >   
> >   /* It's valid after kvm_confidential_guest_init()->kvm_tdx_init() */
> > @@ -211,6 +214,20 @@ int tdx_pre_create_vcpu(CPUState *cpu)
> >           goto out;
> >       }
> >   
> > +    r = -EINVAL;
> > +    if (env->tsc_khz && (env->tsc_khz < TDX_MIN_TSC_FREQUENCY_KHZ ||
> > +                         env->tsc_khz > TDX_MAX_TSC_FREQUENCY_KHZ)) {
> > +        error_report("Invalid TSC %ld KHz, must specify cpu_frequency between [%d, %d] kHz",
> > +                      env->tsc_khz, TDX_MIN_TSC_FREQUENCY_KHZ,
> > +                      TDX_MAX_TSC_FREQUENCY_KHZ);
> > +        goto out;
> > +    }
> > +
> > +    if (env->tsc_khz % (25 * 1000)) {
> > +        error_report("Invalid TSC %ld KHz, it must be multiple of 25MHz", env->tsc_khz);
> > +        goto out;
> > +    }
> > +
> >       r = setup_td_guest_attributes(x86cpu);
> >       if (r) {
> >           goto out;
> > @@ -221,6 +238,7 @@ int tdx_pre_create_vcpu(CPUState *cpu)
> >   
> >       init_vm.attributes = tdx_guest->attributes;
> >       init_vm.max_vcpus = ms->smp.cpus;
> > +    init_vm.tsc_khz = env->tsc_khz;
> >   
> >       r = tdx_vm_ioctl(KVM_TDX_INIT_VM, 0, &init_vm);
> >       if (r < 0) {
> > --
> > 2.27.0