Re: [PATCH v19 111/130] KVM: TDX: Implement callbacks for MSR operations for TDX

Isaku Yamahata
2024-04-04T23:42:39Z

On Wed, Apr 03, 2024 at 08:14:04AM -0700,
Sean Christopherson <seanjc@google.com> wrote:

> On Mon, Feb 26, 2024, isaku.yamahata@intel.com wrote:
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 389bb95d2af0..c8f991b69720 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -1877,6 +1877,76 @@ void tdx_get_exit_info(struct kvm_vcpu *vcpu, u32 *reason,
> > *error_code = 0;
> > }
> >
> > +static bool tdx_is_emulated_kvm_msr(u32 index, bool write)
> > +{
> > + switch (index) {
> > + case MSR_KVM_POLL_CONTROL:
> > + return true;
> > + default:
> > + return false;
> > + }
> > +}
> > +
> > +bool tdx_has_emulated_msr(u32 index, bool write)
> > +{
> > + switch (index) {
> > + case MSR_IA32_UCODE_REV:
> > + case MSR_IA32_ARCH_CAPABILITIES:
> > + case MSR_IA32_POWER_CTL:
> > + case MSR_IA32_CR_PAT:
> > + case MSR_IA32_TSC_DEADLINE:
> > + case MSR_IA32_MISC_ENABLE:
> > + case MSR_PLATFORM_INFO:
> > + case MSR_MISC_FEATURES_ENABLES:
> > + case MSR_IA32_MCG_CAP:
> > + case MSR_IA32_MCG_STATUS:
> > + case MSR_IA32_MCG_CTL:
> > + case MSR_IA32_MCG_EXT_CTL:
> > + case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1:
> > + case MSR_IA32_MC0_CTL2 ... MSR_IA32_MCx_CTL2(KVM_MAX_MCE_BANKS) - 1:
> > + /* MSR_IA32_MCx_{CTL, STATUS, ADDR, MISC, CTL2} */
> > + return true;
> > + case APIC_BASE_MSR ... APIC_BASE_MSR + 0xff:
> > + /*
> > + * x2APIC registers that are virtualized by the CPU can't be
> > + * emulated, KVM doesn't have access to the virtual APIC page.
> > + */
> > + switch (index) {
> > + case X2APIC_MSR(APIC_TASKPRI):
> > + case X2APIC_MSR(APIC_PROCPRI):
> > + case X2APIC_MSR(APIC_EOI):
> > + case X2APIC_MSR(APIC_ISR) ... X2APIC_MSR(APIC_ISR + APIC_ISR_NR):
> > + case X2APIC_MSR(APIC_TMR) ... X2APIC_MSR(APIC_TMR + APIC_ISR_NR):
> > + case X2APIC_MSR(APIC_IRR) ... X2APIC_MSR(APIC_IRR + APIC_ISR_NR):
> > + return false;
> > + default:
> > + return true;
> > + }
> > + case MSR_IA32_APICBASE:
> > + case MSR_EFER:
> > + return !write;
>
> Meh, for literally two MSRs, just open code them in tdx_set_msr() and drop the
> @write param. Or alternatively add:
>
> static bool tdx_is_read_only_msr(u32 msr){
> {
> return msr == MSR_IA32_APICBASE || msr == MSR_EFER;
> }

Sure will add.

>
> > + case 0x4b564d00 ... 0x4b564dff:
>
> This is silly, just do
>
> case MSR_KVM_POLL_CONTROL:
> return false;
>
> and let everything else go through the default statement, no?

Now tdx_is_emulated_kvm_msr() is trivial, will open code it.

> > + /* KVM custom MSRs */
> > + return tdx_is_emulated_kvm_msr(index, write);
> > + default:
> > + return false;
> > + }
> > +}
> > +
> > +int tdx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
> > +{
> > + if (tdx_has_emulated_msr(msr->index, false))
> > + return kvm_get_msr_common(vcpu, msr);
> > + return 1;
>
> Please invert these and make the happy path the not-taken path, i.e.
>
> if (!tdx_has_emulated_msr(msr->index))
> return 1;
>
> return kvm_get_msr_common(vcpu, msr);
>
> The standard kernel pattern is
>
> if (error)
> return <error thingie>
>
> return <happy thingie>
>
> > +}
> > +
> > +int tdx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
> > +{
> > + if (tdx_has_emulated_msr(msr->index, true))
>
> As above:
>
> if (tdx_is_read_only_msr(msr->index))
> return 1;
>
> if (!tdx_has_emulated_msr(msr->index))
> return 1;
>
> return kvm_set_msr_common(vcpu, msr);

Sure, will update them.

> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index d5b18cad9dcd..0e1d3853eeb4 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -90,7 +90,6 @@
> > #include "trace.h"
> >
> > #define MAX_IO_MSRS 256
> > -#define KVM_MAX_MCE_BANKS 32
> >
> > struct kvm_caps kvm_caps __read_mostly = {
> > .supported_mce_cap = MCG_CTL_P | MCG_SER_P,
> > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> > index 4e40c23d66ed..c87b7a777b67 100644
> > --- a/arch/x86/kvm/x86.h
> > +++ b/arch/x86/kvm/x86.h
> > @@ -9,6 +9,8 @@
> > #include "kvm_cache_regs.h"
> > #include "kvm_emulate.h"
> >
> > +#define KVM_MAX_MCE_BANKS 32
>
> Split this to a separate. Yes, it's trivial, but that's _exactly_ why it should
> be in a separate patch. The more trivial refactoring you split out, the more we
> can apply _now_ and take off your hands.

Will split it.
--
Isaku Yamahata <isaku.yamahata@intel.com>