linux - 如何或在 KVM 的 CPUID 仿真代码中修改哪个文件以报告一个虚构的处理器品牌字符串(CPUID 叶 0x0)？

Question

这是要修改的正确 Linux 内核代码吗？我如何进行更改以模拟 CPUID 代码以及我需要更改哪个函数。谢谢

#include <linux/kvm_host.h>
#include <linux/export.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include <linux/sched/stat.h>

#include <asm/processor.h>
#include <asm/user.h>
#include <asm/fpu/xstate.h>
#include "cpuid.h"
#include "lapic.h"
#include "mmu.h"
#include "trace.h"
#include "pmu.h"

static u32 xstate_required_size(u64 xstate_bv, bool compacted)
{
    int feature_bit = 0;
    u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;

    xstate_bv &= XFEATURE_MASK_EXTEND;
    while (xstate_bv) {
        if (xstate_bv & 0x1) {
                u32 eax, ebx, ecx, edx, offset;
                cpuid_count(0xD, feature_bit, &eax, &ebx, &ecx, &edx);
            offset = compacted ? ret : ebx;
            ret = max(ret, offset + eax);
        }

        xstate_bv >>= 1;
        feature_bit++;
    }

    return ret;
}

bool kvm_mpx_supported(void)
{
    return ((host_xcr0 & (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR))
         && kvm_x86_ops->mpx_supported());
}
EXPORT_SYMBOL_GPL(kvm_mpx_supported);

u64 kvm_supported_xcr0(void)
{
    u64 xcr0 = KVM_SUPPORTED_XCR0 & host_xcr0;

    if (!kvm_mpx_supported())
        xcr0 &= ~(XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);

    return xcr0;
}

#define F(x) bit(X86_FEATURE_##x)

/* These are scattered features in cpufeatures.h. */
#define KVM_CPUID_BIT_AVX512_4VNNIW     2
#define KVM_CPUID_BIT_AVX512_4FMAPS     3
#define KF(x) bit(KVM_CPUID_BIT_##x)

int kvm_update_cpuid(struct kvm_vcpu *vcpu)
{
    struct kvm_cpuid_entry2 *best;
    struct kvm_lapic *apic = vcpu->arch.apic;

    best = kvm_find_cpuid_entry(vcpu, 1, 0);
    if (!best)
        return 0;

    /* Update OSXSAVE bit */
    if (boot_cpu_has(X86_FEATURE_XSAVE) && best->function == 0x1) {
        best->ecx &= ~F(OSXSAVE);
        if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE))
            best->ecx |= F(OSXSAVE);
    }

    best->edx &= ~F(APIC);
    if (vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE)
        best->edx |= F(APIC);

    if (apic) {
        if (best->ecx & F(TSC_DEADLINE_TIMER))
            apic->lapic_timer.timer_mode_mask = 3 << 17;
        else
            apic->lapic_timer.timer_mode_mask = 1 << 17;
    }

    best = kvm_find_cpuid_entry(vcpu, 7, 0);
    if (best) {
        /* Update OSPKE bit */
        if (boot_cpu_has(X86_FEATURE_PKU) && best->function == 0x7) {
            best->ecx &= ~F(OSPKE);
            if (kvm_read_cr4_bits(vcpu, X86_CR4_PKE))
                best->ecx |= F(OSPKE);
        }
    }

    best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
    if (!best) {
        vcpu->arch.guest_supported_xcr0 = 0;
        vcpu->arch.guest_xstate_size = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
    } else {
        vcpu->arch.guest_supported_xcr0 =
            (best->eax | ((u64)best->edx << 32)) &
            kvm_supported_xcr0();
        vcpu->arch.guest_xstate_size = best->ebx =
            xstate_required_size(vcpu->arch.xcr0, false);
    }

    best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
    if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
        best->ebx = xstate_required_size(vcpu->arch.xcr0, true);

    /*
     * The existing code assumes virtual address is 48-bit or 57-bit in the
     * canonical address checks; exit if it is ever changed.
     */
    best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
    if (best) {
        int vaddr_bits = (best->eax & 0xff00) >> 8;

        if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
            return -EINVAL;
    }

    /* Update physical-address width */
    vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
    kvm_mmu_reset_context(vcpu);

    kvm_pmu_refresh(vcpu);
    return 0;
}

static int is_efer_nx(void)
{
    unsigned long long efer = 0;

    rdmsrl_safe(MSR_EFER, &efer);
    return efer & EFER_NX;
}

static void cpuid_fix_nx_cap(struct kvm_vcpu *vcpu)
{
    int i;
    struct kvm_cpuid_entry2 *e, *entry;

    entry = NULL;
    for (i = 0; i < vcpu->arch.cpuid_nent; ++i) {
        e = &vcpu->arch.cpuid_entries[i];
        if (e->function == 0x80000001) {
            entry = e;
            break;
        }
    }
    if (entry && (entry->edx & F(NX)) && !is_efer_nx()) {
        entry->edx &= ~F(NX);
        printk(KERN_INFO "kvm: guest NX capability removed\n");
    }
}

int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu)
{
    struct kvm_cpuid_entry2 *best;

    best = kvm_find_cpuid_entry(vcpu, 0x80000000, 0);
    if (!best || best->eax < 0x80000008)
        goto not_found;
    best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
    if (best)
        return best->eax & 0xff;
not_found:
    return 36;
}
EXPORT_SYMBOL_GPL(cpuid_query_maxphyaddr);

/* when an old userspace process fills a new kernel module */
int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
                 struct kvm_cpuid *cpuid,
                 struct kvm_cpuid_entry __user *entries)
{
    int r, i;
    struct kvm_cpuid_entry *cpuid_entries = NULL;

    r = -E2BIG;
    if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
        goto out;
    r = -ENOMEM;
    if (cpuid->nent) {
        cpuid_entries = vmalloc(sizeof(struct kvm_cpuid_entry) *
                    cpuid->nent);
        if (!cpuid_entries)
            goto out;
        r = -EFAULT;
        if (copy_from_user(cpuid_entries, entries,
                   cpuid->nent * sizeof(struct kvm_cpuid_entry)))
            goto out;
    }
    for (i = 0; i < cpuid->nent; i++) {
        vcpu->arch.cpuid_entries[i].function = cpuid_entries[i].function;
        vcpu->arch.cpuid_entries[i].eax = cpuid_entries[i].eax;
        vcpu->arch.cpuid_entries[i].ebx = cpuid_entries[i].ebx;
        vcpu->arch.cpuid_entries[i].ecx = cpuid_entries[i].ecx;
        vcpu->arch.cpuid_entries[i].edx = cpuid_entries[i].edx;
        vcpu->arch.cpuid_entries[i].index = 0;
        vcpu->arch.cpuid_entries[i].flags = 0;
        vcpu->arch.cpuid_entries[i].padding[0] = 0;
        vcpu->arch.cpuid_entries[i].padding[1] = 0;
        vcpu->arch.cpuid_entries[i].padding[2] = 0;
    }
    vcpu->arch.cpuid_nent = cpuid->nent;
    cpuid_fix_nx_cap(vcpu);
    kvm_apic_set_version(vcpu);
    kvm_x86_ops->cpuid_update(vcpu);
    r = kvm_update_cpuid(vcpu);

out:
    vfree(cpuid_entries);
    return r;
}

int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
                  struct kvm_cpuid2 *cpuid,
                  struct kvm_cpuid_entry2 __user *entries)
{
    int r;

    r = -E2BIG;
    if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
        goto out;
    r = -EFAULT;
    if (copy_from_user(&vcpu->arch.cpuid_entries, entries,
               cpuid->nent * sizeof(struct kvm_cpuid_entry2)))
        goto out;
    vcpu->arch.cpuid_nent = cpuid->nent;
    kvm_apic_set_version(vcpu);
    kvm_x86_ops->cpuid_update(vcpu);
    r = kvm_update_cpuid(vcpu);
out:
    return r;
}

int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
                  struct kvm_cpuid2 *cpuid,
                  struct kvm_cpuid_entry2 __user *entries)
{
    int r;

    r = -E2BIG;
    if (cpuid->nent < vcpu->arch.cpuid_nent)
        goto out;
    r = -EFAULT;
    if (copy_to_user(entries, &vcpu->arch.cpuid_entries,
             vcpu->arch.cpuid_nent * sizeof(struct kvm_cpuid_entry2)))
        goto out;
    return 0;

out:
    cpuid->nent = vcpu->arch.cpuid_nent;
    return r;
}

static void cpuid_mask(u32 *word, int wordnum)
{
    *word &= boot_cpu_data.x86_capability[wordnum];
}

static void do_cpuid_1_ent(struct kvm_cpuid_entry2 *entry, u32 function,
               u32 index)
{
    entry->function = function;
    entry->index = index;
    cpuid_count(entry->function, entry->index,
            &entry->eax, &entry->ebx, &entry->ecx, &entry->edx);
    entry->flags = 0;
}

static int __do_cpuid_ent_emulated(struct kvm_cpuid_entry2 *entry,
                   u32 func, u32 index, int *nent, int maxnent)
{
    switch (func) {
    case 0:
        entry->eax = 1;     /* only one leaf currently */
        ++*nent;
        break;
    case 1:
        entry->ecx = F(MOVBE);
        ++*nent;
        break;
    default:
        break;
    }

    entry->function = func;
    entry->index = index;

    return 0;
}

static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
                 u32 index, int *nent, int maxnent)
{
    int r;
    unsigned f_nx = is_efer_nx() ? F(NX) : 0;
#ifdef CONFIG_X86_64
    unsigned f_gbpages = (kvm_x86_ops->get_lpage_level() == PT_PDPE_LEVEL)
                ? F(GBPAGES) : 0;
    unsigned f_lm = F(LM);
#else
    unsigned f_gbpages = 0;
    unsigned f_lm = 0;
#endif
    unsigned f_rdtscp = kvm_x86_ops->rdtscp_supported() ? F(RDTSCP) : 0;
    unsigned f_invpcid = kvm_x86_ops->invpcid_supported() ? F(INVPCID) : 0;
    unsigned f_mpx = kvm_mpx_supported() ? F(MPX) : 0;
    unsigned f_xsaves = kvm_x86_ops->xsaves_supported() ? F(XSAVES) : 0;

    /* cpuid 1.edx */
    const u32 kvm_cpuid_1_edx_x86_features =
        F(FPU) | F(VME) | F(DE) | F(PSE) |
        F(TSC) | F(MSR) | F(PAE) | F(MCE) |
        F(CX8) | F(APIC) | 0 /* Reserved */ | F(SEP) |
        F(MTRR) | F(PGE) | F(MCA) | F(CMOV) |
        F(PAT) | F(PSE36) | 0 /* PSN */ | F(CLFLUSH) |
        0 /* Reserved, DS, ACPI */ | F(MMX) |
        F(FXSR) | F(XMM) | F(XMM2) | F(SELFSNOOP) |
        0 /* HTT, TM, Reserved, PBE */;
    /* cpuid 0x80000001.edx */
    const u32 kvm_cpuid_8000_0001_edx_x86_features =
        F(FPU) | F(VME) | F(DE) | F(PSE) |
        F(TSC) | F(MSR) | F(PAE) | F(MCE) |
        F(CX8) | F(APIC) | 0 /* Reserved */ | F(SYSCALL) |
        F(MTRR) | F(PGE) | F(MCA) | F(CMOV) |
        F(PAT) | F(PSE36) | 0 /* Reserved */ |
        f_nx | 0 /* Reserved */ | F(MMXEXT) | F(MMX) |
        F(FXSR) | F(FXSR_OPT) | f_gbpages | f_rdtscp |
        0 /* Reserved */ | f_lm | F(3DNOWEXT) | F(3DNOW);
    /* cpuid 1.ecx */
    const u32 kvm_cpuid_1_ecx_x86_features =
        /* NOTE: MONITOR (and MWAIT) are emulated as NOP,
         * but *not* advertised to guests via CPUID ! */
        F(XMM3) | F(PCLMULQDQ) | 0 /* DTES64, MONITOR */ |
        0 /* DS-CPL, VMX, SMX, EST */ |
        0 /* TM2 */ | F(SSSE3) | 0 /* CNXT-ID */ | 0 /* Reserved */ |
        F(FMA) | F(CX16) | 0 /* xTPR Update, PDCM */ |
        F(PCID) | 0 /* Reserved, DCA */ | F(XMM4_1) |
        F(XMM4_2) | F(X2APIC) | F(MOVBE) | F(POPCNT) |
        0 /* Reserved*/ | F(AES) | F(XSAVE) | 0 /* OSXSAVE */ | F(AVX) |
        F(F16C) | F(RDRAND);
    /* cpuid 0x80000001.ecx */
    const u32 kvm_cpuid_8000_0001_ecx_x86_features =
        F(LAHF_LM) | F(CMP_LEGACY) | 0 /*SVM*/ | 0 /* ExtApicSpace */ |
        F(CR8_LEGACY) | F(ABM) | F(SSE4A) | F(MISALIGNSSE) |
        F(3DNOWPREFETCH) | F(OSVW) | 0 /* IBS */ | F(XOP) |
        0 /* SKINIT, WDT, LWP */ | F(FMA4) | F(TBM);

    /* cpuid 0xC0000001.edx */
    const u32 kvm_cpuid_C000_0001_edx_x86_features =
        F(XSTORE) | F(XSTORE_EN) | F(XCRYPT) | F(XCRYPT_EN) |
        F(ACE2) | F(ACE2_EN) | F(PHE) | F(PHE_EN) |
        F(PMM) | F(PMM_EN);

    /* cpuid 7.0.ebx */
    const u32 kvm_cpuid_7_0_ebx_x86_features =
        F(FSGSBASE) | F(BMI1) | F(HLE) | F(AVX2) | F(SMEP) |
        F(BMI2) | F(ERMS) | f_invpcid | F(RTM) | f_mpx | F(RDSEED) |
        F(ADX) | F(SMAP) | F(AVX512IFMA) | F(AVX512F) | F(AVX512PF) |
        F(AVX512ER) | F(AVX512CD) | F(CLFLUSHOPT) | F(CLWB) | F(AVX512DQ) |
        F(SHA_NI) | F(AVX512BW) | F(AVX512VL);

    /* cpuid 0xD.1.eax */
    const u32 kvm_cpuid_D_1_eax_x86_features =
        F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | f_xsaves;

    /* cpuid 7.0.ecx*/
    const u32 kvm_cpuid_7_0_ecx_x86_features =
        F(AVX512VBMI) | F(LA57) | F(PKU) |
        0 /*OSPKE*/ | F(AVX512_VPOPCNTDQ);

    /* cpuid 7.0.edx*/
    const u32 kvm_cpuid_7_0_edx_x86_features =
        KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS);

    /* all calls to cpuid_count() should be made on the same cpu */
    get_cpu();

    r = -E2BIG;

    if (*nent >= maxnent)
        goto out;

    do_cpuid_1_ent(entry, function, index);
    ++*nent;

    switch (function) {
    case 0:
        entry->eax = min(entry->eax, (u32)0xd);
        break;
    case 1:
        entry->edx &= kvm_cpuid_1_edx_x86_features;
        cpuid_mask(&entry->edx, CPUID_1_EDX);
        entry->ecx &= kvm_cpuid_1_ecx_x86_features;
        cpuid_mask(&entry->ecx, CPUID_1_ECX);
        /* we support x2apic emulation even if host does not support
         * it since we emulate x2apic in software */
        entry->ecx |= F(X2APIC);
        break;
    /* function 2 entries are STATEFUL. That is, repeated cpuid commands
     * may return different values. This forces us to get_cpu() before
     * issuing the first command, and also to emulate this annoying behavior
     * in kvm_emulate_cpuid() using KVM_CPUID_FLAG_STATE_READ_NEXT */
    case 2: {
        int t, times = entry->eax & 0xff;

        entry->flags |= KVM_CPUID_FLAG_STATEFUL_FUNC;
        entry->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
        for (t = 1; t < times; ++t) {
            if (*nent >= maxnent)
                goto out;

            do_cpuid_1_ent(&entry[t], function, 0);
            entry[t].flags |= KVM_CPUID_FLAG_STATEFUL_FUNC;
            ++*nent;
        }
        break;
    }
    /* function 4 has additional index. */
    case 4: {
        int i, cache_type;

        entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
        /* read more entries until cache_type is zero */
        for (i = 1; ; ++i) {
            if (*nent >= maxnent)
                goto out;

            cache_type = entry[i - 1].eax & 0x1f;
            if (!cache_type)
                break;
            do_cpuid_1_ent(&entry[i], function, i);
            entry[i].flags |=
                   KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
            ++*nent;
        }
        break;
    }
    case 6: /* Thermal management */
        entry->eax = 0x4; /* allow ARAT */
        entry->ebx = 0;
        entry->ecx = 0;
        entry->edx = 0;
        break;
    case 7: {
        entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
        /* Mask ebx against host capability word 9 */
        if (index == 0) {
            entry->ebx &= kvm_cpuid_7_0_ebx_x86_features;
            cpuid_mask(&entry->ebx, CPUID_7_0_EBX);
            // TSC_ADJUST is emulated
            entry->ebx |= F(TSC_ADJUST);
            entry->ecx &= kvm_cpuid_7_0_ecx_x86_features;
            cpuid_mask(&entry->ecx, CPUID_7_ECX);
            /* PKU is not yet implemented for shadow paging. */
            if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
                entry->ecx &= ~F(PKU);
            entry->edx &= kvm_cpuid_7_0_edx_x86_features;
            entry->edx &= get_scattered_cpuid_leaf(7, 0, CPUID_EDX);
        } else {
            entry->ebx = 0;
            entry->ecx = 0;
            entry->edx = 0;
        }
        entry->eax = 0;
        break;
    }
    case 9:
        break;
    case 0xa: { /* Architectural Performance Monitoring */
        struct x86_pmu_capability cap;
        union cpuid10_eax eax;
        union cpuid10_edx edx;

        perf_get_x86_pmu_capability(&cap);

        /*
         * Only support guest architectural pmu on a host
         * with architectural pmu.
         */
        if (!cap.version)
            memset(&cap, 0, sizeof(cap));

        eax.split.version_id = min(cap.version, 2);
        eax.split.num_counters = cap.num_counters_gp;
        eax.split.bit_width = cap.bit_width_gp;
        eax.split.mask_length = cap.events_mask_len;

        edx.split.num_counters_fixed = cap.num_counters_fixed;
        edx.split.bit_width_fixed = cap.bit_width_fixed;
        edx.split.reserved = 0;

        entry->eax = eax.full;
        entry->ebx = cap.events_mask;
        entry->ecx = 0;
        entry->edx = edx.full;
        break;
    }
    /* function 0xb has additional index. */
    case 0xb: {
        int i, level_type;

        entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
        /* read more entries until level_type is zero */
        for (i = 1; ; ++i) {
            if (*nent >= maxnent)
                goto out;

            level_type = entry[i - 1].ecx & 0xff00;
            if (!level_type)
                break;
            do_cpuid_1_ent(&entry[i], function, i);
            entry[i].flags |=
                   KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
            ++*nent;
        }
        break;
    }
    case 0xd: {
        int idx, i;
        u64 supported = kvm_supported_xcr0();

        entry->eax &= supported;
        entry->ebx = xstate_required_size(supported, false);
        entry->ecx = entry->ebx;
        entry->edx &= supported >> 32;
        entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
        if (!supported)
            break;

        for (idx = 1, i = 1; idx < 64; ++idx) {
            u64 mask = ((u64)1 << idx);
            if (*nent >= maxnent)
                goto out;

            do_cpuid_1_ent(&entry[i], function, idx);
            if (idx == 1) {
                entry[i].eax &= kvm_cpuid_D_1_eax_x86_features;
                cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
                entry[i].ebx = 0;
                if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
                    entry[i].ebx =
                        xstate_required_size(supported,
                                     true);
            } else {
                if (entry[i].eax == 0 || !(supported & mask))
                    continue;
                if (WARN_ON_ONCE(entry[i].ecx & 1))
                    continue;
            }
            entry[i].ecx = 0;
            entry[i].edx = 0;
            entry[i].flags |=
                   KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
            ++*nent;
            ++i;
        }
        break;
    }
    case KVM_CPUID_SIGNATURE: {
        static const char signature[12] = "KVMKVMKVM\0\0";
        const u32 *sigptr = (const u32 *)signature;
        entry->eax = KVM_CPUID_FEATURES;
        entry->ebx = sigptr[0];
        entry->ecx = sigptr[1];
        entry->edx = sigptr[2];
        break;
    }
    case KVM_CPUID_FEATURES:
        entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
                 (1 << KVM_FEATURE_NOP_IO_DELAY) |
                 (1 << KVM_FEATURE_CLOCKSOURCE2) |
                 (1 << KVM_FEATURE_ASYNC_PF) |
                 (1 << KVM_FEATURE_PV_EOI) |
                 (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
                 (1 << KVM_FEATURE_PV_UNHALT);

        if (sched_info_on())
            entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);

        entry->ebx = 0;
        entry->ecx = 0;
        entry->edx = 0;
        break;
    case 0x80000000:
        entry->eax = min(entry->eax, 0x8000001a);
        break;
    case 0x80000001:
        entry->edx &= kvm_cpuid_8000_0001_edx_x86_features;
        cpuid_mask(&entry->edx, CPUID_8000_0001_EDX);
        entry->ecx &= kvm_cpuid_8000_0001_ecx_x86_features;
        cpuid_mask(&entry->ecx, CPUID_8000_0001_ECX);
        break;
    case 0x80000007: /* Advanced power management */
        /* invariant TSC is CPUID.80000007H:EDX[8] */
        entry->edx &= (1 << 8);
        /* mask against host */
        entry->edx &= boot_cpu_data.x86_power;
        entry->eax = entry->ebx = entry->ecx = 0;
        break;
    case 0x80000008: {
        unsigned g_phys_as = (entry->eax >> 16) & 0xff;
        unsigned virt_as = max((entry->eax >> 8) & 0xff, 48U);
        unsigned phys_as = entry->eax & 0xff;

        if (!g_phys_as)
            g_phys_as = phys_as;
        entry->eax = g_phys_as | (virt_as << 8);
        entry->ebx = entry->edx = 0;
        break;
    }
    case 0x80000019:
        entry->ecx = entry->edx = 0;
        break;
    case 0x8000001a:
        break;
    case 0x8000001d:
        break;
    /*Add support for Centaur's CPUID instruction*/
    case 0xC0000000:
        /*Just support up to 0xC0000004 now*/
        entry->eax = min(entry->eax, 0xC0000004);
        break;
    case 0xC0000001:
        entry->edx &= kvm_cpuid_C000_0001_edx_x86_features;
        cpuid_mask(&entry->edx, CPUID_C000_0001_EDX);
        break;
    case 3: /* Processor serial number */
    case 5: /* MONITOR/MWAIT */
    case 0xC0000002:
    case 0xC0000003:
    case 0xC0000004:
    default:
        entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
        break;
    }

    kvm_x86_ops->set_supported_cpuid(function, entry);

    r = 0;

out:
    put_cpu();

    return r;
}

static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 func,
            u32 idx, int *nent, int maxnent, unsigned int type)
{
    if (type == KVM_GET_EMULATED_CPUID)
        return __do_cpuid_ent_emulated(entry, func, idx, nent, maxnent);

    return __do_cpuid_ent(entry, func, idx, nent, maxnent);
}

#undef F

struct kvm_cpuid_param {
    u32 func;
    u32 idx;
    bool has_leaf_count;
    bool (*qualifier)(const struct kvm_cpuid_param *param);
};

static bool is_centaur_cpu(const struct kvm_cpuid_param *param)
{
    return boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR;
}

static bool sanity_check_entries(struct kvm_cpuid_entry2 __user *entries,
                 __u32 num_entries, unsigned int ioctl_type)
{
    int i;
    __u32 pad[3];

    if (ioctl_type != KVM_GET_EMULATED_CPUID)
        return false;

    /*
     * We want to make sure that ->padding is being passed clean from
     * userspace in case we want to use it for something in the future.
     *
     * Sadly, this wasn't enforced for KVM_GET_SUPPORTED_CPUID and so we
     * have to give ourselves satisfied only with the emulated side. /me
     * sheds a tear.
     */
    for (i = 0; i < num_entries; i++) {
        if (copy_from_user(pad, entries[i].padding, sizeof(pad)))
            return true;

        if (pad[0] || pad[1] || pad[2])
            return true;
    }
    return false;
}

int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
                struct kvm_cpuid_entry2 __user *entries,
                unsigned int type)
{
    struct kvm_cpuid_entry2 *cpuid_entries;
    int limit, nent = 0, r = -E2BIG, i;
    u32 func;
    static const struct kvm_cpuid_param param[] = {
        { .func = 0, .has_leaf_count = true },
        { .func = 0x80000000, .has_leaf_count = true },
        { .func = 0xC0000000, .qualifier = is_centaur_cpu, .has_leaf_count = true },
        { .func = KVM_CPUID_SIGNATURE },
        { .func = KVM_CPUID_FEATURES },
    };

    if (cpuid->nent < 1)
        goto out;
    if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
        cpuid->nent = KVM_MAX_CPUID_ENTRIES;

    if (sanity_check_entries(entries, cpuid->nent, type))
        return -EINVAL;

    r = -ENOMEM;
    cpuid_entries = vzalloc(sizeof(struct kvm_cpuid_entry2) * cpuid->nent);
    if (!cpuid_entries)
        goto out;

    r = 0;
    for (i = 0; i < ARRAY_SIZE(param); i++) {
        const struct kvm_cpuid_param *ent = &param[i];

        if (ent->qualifier && !ent->qualifier(ent))
            continue;

        r = do_cpuid_ent(&cpuid_entries[nent], ent->func, ent->idx,
                &nent, cpuid->nent, type);

        if (r)
            goto out_free;

        if (!ent->has_leaf_count)
            continue;

        limit = cpuid_entries[nent - 1].eax;
        for (func = ent->func + 1; func <= limit && nent < cpuid->nent && r == 0; ++func)
            r = do_cpuid_ent(&cpuid_entries[nent], func, ent->idx,
                     &nent, cpuid->nent, type);

        if (r)
            goto out_free;
    }

    r = -EFAULT;
    if (copy_to_user(entries, cpuid_entries,
             nent * sizeof(struct kvm_cpuid_entry2)))
        goto out_free;
    cpuid->nent = nent;
    r = 0;

out_free:
    vfree(cpuid_entries);
out:
    return r;
}

static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
{
    struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
    struct kvm_cpuid_entry2 *ej;
    int j = i;
    int nent = vcpu->arch.cpuid_nent;

    e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
    /* when no next entry is found, the current entry[i] is reselected */
    do {
        j = (j + 1) % nent;
        ej = &vcpu->arch.cpuid_entries[j];
    } while (ej->function != e->function);

    ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;

    return j;
}

/* find an entry with matching function, matching index (if needed), and that
 * should be read next (if it's stateful) */
static int is_matching_cpuid_entry(struct kvm_cpuid_entry2 *e,
    u32 function, u32 index)
{
    if (e->function != function)
        return 0;
    if ((e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX) && e->index != index)
        return 0;
    if ((e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC) &&
        !(e->flags & KVM_CPUID_FLAG_STATE_READ_NEXT))
        return 0;
    return 1;
}

struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
                          u32 function, u32 index)
{
    int i;
    struct kvm_cpuid_entry2 *best = NULL;

    for (i = 0; i < vcpu->arch.cpuid_nent; ++i) {
        struct kvm_cpuid_entry2 *e;

        e = &vcpu->arch.cpuid_entries[i];
        if (is_matching_cpuid_entry(e, function, index)) {
            if (e->flags & KVM_CPUID_FLAG_STATEFUL_FUNC)
                move_to_next_stateful_cpuid_entry(vcpu, i);
            best = e;
            break;
        }
    }
    return best;
}
EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);

/*
 * If no match is found, check whether we exceed the vCPU's limit
 * and return the content of the highest valid _standard_ leaf instead.
 * This is to satisfy the CPUID specification.
 */
static struct kvm_cpuid_entry2* check_cpuid_limit(struct kvm_vcpu *vcpu,
                                                  u32 function, u32 index)
{
    struct kvm_cpuid_entry2 *maxlevel;

    maxlevel = kvm_find_cpuid_entry(vcpu, function & 0x80000000, 0);
    if (!maxlevel || maxlevel->eax >= function)
        return NULL;
    if (function & 0x80000000) {
        maxlevel = kvm_find_cpuid_entry(vcpu, 0, 0);
        if (!maxlevel)
            return NULL;
    }
    return kvm_find_cpuid_entry(vcpu, maxlevel->eax, index);
}

bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
           u32 *ecx, u32 *edx, bool check_limit)
{
    u32 function = *eax, index = *ecx;
    struct kvm_cpuid_entry2 *best;
    bool entry_found = true;

    best = kvm_find_cpuid_entry(vcpu, function, index);

    if (!best) {
        entry_found = false;
        if (!check_limit)
            goto out;

        best = check_cpuid_limit(vcpu, function, index);
    }

out:
    if (best) {
        *eax = best->eax;
        *ebx = best->ebx;
        *ecx = best->ecx;
        *edx = best->edx;
    } else
        *eax = *ebx = *ecx = *edx = 0;
    trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, entry_found);
    return entry_found;
}
EXPORT_SYMBOL_GPL(kvm_cpuid);

int kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
{
    u32 eax, ebx, ecx, edx;

    if (cpuid_fault_enabled(vcpu) && !kvm_require_cpl(vcpu, 0))
        return 1;

    eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
    ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
    kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx, true);
    kvm_register_write(vcpu, VCPU_REGS_RAX, eax);
    kvm_register_write(vcpu, VCPU_REGS_RBX, ebx);
    kvm_register_write(vcpu, VCPU_REGS_RCX, ecx);
    kvm_register_write(vcpu, VCPU_REGS_RDX, edx);
    return kvm_skip_emulated_instruction(vcpu);
}
EXPORT_SYMBOL_GPL(kvm_emulate_cpuid);

我想将代码添加/编辑到你的 linux 树中的 KVM(我从 github 克隆内核)，重建内核并引导到修改后的内核并运行用户模式的 c 程序，如

#include <stdio.h>
#include <cpuid.h>
#include <stdint.h>

    int
    main(int argc, char **argv)
    {
     uint32_t eax, ebx, ecx, edx;

     __cpuid(0x0, eax, ebx, ecx, edx);

     printf("CPUID(0x0).EAX=0x%x\n", eax);
     printf("CPUID(0x0).EBX=0x%x\n", ebx);
     printf("CPUID(0x0).ECX=0x%x\n", ecx);
     printf("CPUID(0x0).EDX=0x%x\n", edx);

     return 0;
    }

得到类似的输出

CPUID(0x0) Brand String = GenuineIntel
CPUID(0x4FFFFFFF)
CPUID(0x0) Brand String = SOME TEXT
CPUID(0x4FFFFFFF)

Answer 1

内核本身不实现任何特定的 CPUID 模拟；这是由 KVM 客户端实现的，比如 QEMU。例如，here's the relevant code in QEMU ，它已经实现了许多虚构的处理器品牌，例如“QEMU Virtual CPU”。

此外，KVM CPUID 模拟仅影响运行该内核的机器托管的虚拟机。它不会影响该机器上的普通用户空间应用程序。