Building CentOS 6 kernel with KVM support fails due to MMU

Question

When building the latest Linux kernel for CentOS it turns up the following error

CC [M] arch/x86/kernel/iosf_mbi.o CC arch/x86/kvm/../../../virt/kvm/kvm_main.o CC arch/x86/kvm/../../../virt/kvm/coalesced_mmio.o CC arch/x86/kvm/../../../virt/kvm/eventfd.o CC arch/x86/kvm/../../../virt/kvm/irqchip.o CC arch/x86/kvm/../../../virt/kvm/vfio.o CC arch/x86/kvm/../../../virt/kvm/async_pf.o CC arch/x86/kvm/x86.o arch/x86/kvm/x86.c: In function ‘kvm_write_tsc’: arch/x86/kvm/x86.c:1290: warning: ‘already_matched’ may be used uninitialized > in this function CC arch/x86/kvm/mmu.o arch/x86/kvm/mmu.c: In function ‘kvm_mmu_pte_write’: arch/x86/kvm/mmu.c:4219: error: unknown field ‘cr0_wp’ specified in > initializer arch/x86/kvm/mmu.c:4220: error: unknown field ‘cr4_pae’ specified in initializer arch/x86/kvm/mmu.c:4220: warning: excess elements in union initializer arch/x86/kvm/mmu.c:4220: warning: (near initialization for ‘(anonymous)’) arch/x86/kvm/mmu.c:4221: error: unknown field ‘nxe’ specified in initializer arch/x86/kvm/mmu.c:4221: warning: excess elements in union initializer arch/x86/kvm/mmu.c:4221: warning: (near initialization for ‘(anonymous)’) arch/x86/kvm/mmu.c:4222: error: unknown field ‘smep_andnot_wp’ specified in initializer arch/x86/kvm/mmu.c:4222: warning: excess elements in union initializer arch/x86/kvm/mmu.c:4222: warning: (near initialization for ‘(anonymous)’) arch/x86/kvm/mmu.c:4223: error: unknown field ‘smap_andnot_wp’ specified in initializer arch/x86/kvm/mmu.c:4223: warning: excess elements in union initializer arch/x86/kvm/mmu.c:4223: warning: (near initialization for ‘(anonymous)’) make[2]: * [arch/x86/kvm/mmu.o] Error 1 make[1]: * [arch/x86/kvm] Error 2 make: *** [arch/x86] Error 2

I've disabled MMU under the KVM menu but it still comes up in the compile, I've tried a make clean as well

Here's the build config: http://sprunge.us/YdcN

Anything that I'm missing?

Answer 1

This is a coding mistake found in linux-4.0.5/arch/x86/kvm/mmu.c file. You can comment those lines because that is a union variable used to allocate page table details as it is not much important.

or:

You can replace the function kvm_mmu_pte_write() definition with below code to correct the mistake

void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
                   const u8 *new, int bytes) {
    gfn_t gfn = gpa >> PAGE_SHIFT;
    struct kvm_mmu_page *sp;
    LIST_HEAD(invalid_list);
    u64 entry, gentry, *spte;
    int npte;
    bool remote_flush, local_flush, zap_page;

    struct kvm_mmu *context = &vcpu->arch.mmu;

    union kvm_mmu_page_role mask = (union kvm_mmu_page_role) {
        context->base_role.cr0_wp = 1,
        context->base_role.cr4_pae = 1,
        context->base_role.nxe = 1,
        context->base_role.smep_andnot_wp = 1,
        context->base_role.smap_andnot_wp = 1
    };

    /*
     * If we don't have indirect shadow pages, it means no page is
     * write-protected, so we can exit simply.
     */
    if (!ACCESS_ONCE(vcpu->kvm->arch.indirect_shadow_pages))
            return;

    zap_page = remote_flush = local_flush = false;

    pgprintk("%s: gpa %llx bytes %d\n", __func__, gpa, bytes);

    gentry = mmu_pte_write_fetch_gpte(vcpu, &gpa, new, &bytes);

    /*
     * No need to care whether allocation memory is successful
     * or not since pte prefetch is skiped if it does not have
     * enough objects in the cache.
     */
    mmu_topup_memory_caches(vcpu);

    spin_lock(&vcpu->kvm->mmu_lock);
    ++vcpu->kvm->stat.mmu_pte_write;
    kvm_mmu_audit(vcpu, AUDIT_PRE_PTE_WRITE);

    for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn) {
            if (detect_write_misaligned(sp, gpa, bytes) ||
                  detect_write_flooding(sp)) {
                    zap_page |= !!kvm_mmu_prepare_zap_page(vcpu->kvm, sp,
                                                 &invalid_list);
                    ++vcpu->kvm->stat.mmu_flooded;
                    continue;
            }

            spte = get_written_sptes(sp, gpa, &npte);
            if (!spte)
                    continue;

            local_flush = true;
            while (npte--) {
                    entry = *spte;
                    mmu_page_zap_pte(vcpu->kvm, sp, spte);
                    if (gentry &&
                          !((sp->role.word ^ vcpu->arch.mmu.base_role.word)
                          & mask.word) && rmap_can_add(vcpu))
                            mmu_pte_write_new_pte(vcpu, sp, spte, &gentry);
                    if (need_remote_flush(entry, *spte))
                            remote_flush = true;
                    ++spte;
            }
    }
    mmu_pte_write_flush_tlb(vcpu, zap_page, remote_flush, local_flush);
    kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
    kvm_mmu_audit(vcpu, AUDIT_POST_PTE_WRITE);
    spin_unlock(&vcpu->kvm->mmu_lock);
}

Make the changes and compile the code again. it works for me.