Re: [PATCH v19 082/130] KVM: TDX: restore user ret MSRs

Isaku Yamahata
2024-04-12T20:32:45Z

On Sun, Apr 07, 2024 at 01:59:03PM +0800,
Binbin Wu <binbin.wu@linux.intel.com> wrote:

>
>
> On 2/26/2024 4:26 PM, isaku.yamahata@intel.com wrote:
> > From: Isaku Yamahata <isaku.yamahata@intel.com>
> >
> > Several user ret MSRs are clobbered on TD exit. Restore those values on
> > TD exit
>
> Here "Restore" is not accurate, since the previous patch just updates the
> cached value on TD exit.

Sure, let me update it.

> > and before returning to ring 3. Because TSX_CTRL requires special
> > treat, this patch doesn't address it.
> >
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> > arch/x86/kvm/vmx/tdx.c | 43 ++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 43 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 199226c6cf55..7e2b1e554246 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -535,6 +535,28 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> > */
> > }
> > +struct tdx_uret_msr {
> > + u32 msr;
> > + unsigned int slot;
> > + u64 defval;
> > +};
> > +
> > +static struct tdx_uret_msr tdx_uret_msrs[] = {
> > + {.msr = MSR_SYSCALL_MASK, .defval = 0x20200 },
> > + {.msr = MSR_STAR,},
> > + {.msr = MSR_LSTAR,},
> > + {.msr = MSR_TSC_AUX,},
> > +};
> > +
> > +static void tdx_user_return_update_cache(void)
> > +{
> > + int i;
> > +
> > + for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++)
> > + kvm_user_return_update_cache(tdx_uret_msrs[i].slot,
> > + tdx_uret_msrs[i].defval);
> > +}
> > +
> > static void tdx_restore_host_xsave_state(struct kvm_vcpu *vcpu)
> > {
> > struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
> > @@ -627,6 +649,7 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
> > tdx_vcpu_enter_exit(tdx);
> > + tdx_user_return_update_cache();
> > tdx_restore_host_xsave_state(vcpu);
> > tdx->host_state_need_restore = true;
> > @@ -1972,6 +1995,26 @@ int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> > return -EINVAL;
> > }
> > + for (i = 0; i < ARRAY_SIZE(tdx_uret_msrs); i++) {
> > + /*
> > + * Here it checks if MSRs (tdx_uret_msrs) can be saved/restored
> > + * before returning to user space.
> > + *
> > + * this_cpu_ptr(user_return_msrs)->registered isn't checked
> > + * because the registration is done at vcpu runtime by
> > + * kvm_set_user_return_msr().
> Should be tdx_user_return_update_cache(), if it's the final API name.

Yes, it will be tdx_user_reutrn_msr_update_cache().

> > + * Here is setting up cpu feature before running vcpu,
> > + * registered is already false.
>                                   ^
>                            remove "already"?

We can this sentence.
--
Isaku Yamahata <isaku.yamahata@intel.com>