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    SubjectRe: [PATCH v19 111/130] KVM: TDX: Implement callbacks for MSR operations for TDX
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    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;
    }

    > + 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?

    > + /* 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);

    > 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.

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