Convert gfn_to_pfn() to use get_user_pages_fast(), which can do lockless pagetable lookups. Kernel compilation on 4-way guest is 3.7% faster on VMX.
Andrea, please review (especially mmu notifiers synchronization). kvm_vm_fault, used by older userspace without CAP_USER_MEMORY, had gfn_to_page opencoded without VM_PFNMAP support (hopefully thats not an issue). A compat version of get_user_pages_fast() can be found in mm/util.c. Index: kvm/arch/x86/kvm/mmu.c =================================================================== --- kvm.orig/arch/x86/kvm/mmu.c +++ kvm/arch/x86/kvm/mmu.c @@ -405,16 +405,19 @@ static int host_largepage_backed(struct { struct vm_area_struct *vma; unsigned long addr; + int ret = 0; addr = gfn_to_hva(kvm, gfn); if (kvm_is_error_hva(addr)) - return 0; + return ret; + down_read(¤t->mm->mmap_sem); vma = find_vma(current->mm, addr); if (vma && is_vm_hugetlb_page(vma)) - return 1; + ret = 1; + up_read(¤t->mm->mmap_sem); - return 0; + return ret; } static int is_largepage_backed(struct kvm_vcpu *vcpu, gfn_t large_gfn) @@ -1137,9 +1140,7 @@ struct page *gva_to_page(struct kvm_vcpu if (gpa == UNMAPPED_GVA) return NULL; - down_read(¤t->mm->mmap_sem); page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT); - up_read(¤t->mm->mmap_sem); return page; } @@ -1327,16 +1328,14 @@ static int nonpaging_map(struct kvm_vcpu pfn_t pfn; unsigned long mmu_seq; - down_read(¤t->mm->mmap_sem); if (is_largepage_backed(vcpu, gfn & ~(KVM_PAGES_PER_HPAGE-1))) { gfn &= ~(KVM_PAGES_PER_HPAGE-1); largepage = 1; } mmu_seq = vcpu->kvm->mmu_notifier_seq; - /* implicit mb(), we'll read before PT lock is unlocked */ + smp_rmb(); pfn = gfn_to_pfn(vcpu->kvm, gfn); - up_read(¤t->mm->mmap_sem); /* mmio */ if (is_error_pfn(pfn)) { @@ -1485,15 +1484,13 @@ static int tdp_page_fault(struct kvm_vcp if (r) return r; - down_read(¤t->mm->mmap_sem); if (is_largepage_backed(vcpu, gfn & ~(KVM_PAGES_PER_HPAGE-1))) { gfn &= ~(KVM_PAGES_PER_HPAGE-1); largepage = 1; } mmu_seq = vcpu->kvm->mmu_notifier_seq; - /* implicit mb(), we'll read before PT lock is unlocked */ + smp_rmb(); pfn = gfn_to_pfn(vcpu->kvm, gfn); - up_read(¤t->mm->mmap_sem); if (is_error_pfn(pfn)) { kvm_release_pfn_clean(pfn); return 1; @@ -1806,15 +1803,13 @@ static void mmu_guess_page_from_pte_writ return; gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT; - down_read(¤t->mm->mmap_sem); if (is_large_pte(gpte) && is_largepage_backed(vcpu, gfn)) { gfn &= ~(KVM_PAGES_PER_HPAGE-1); vcpu->arch.update_pte.largepage = 1; } vcpu->arch.update_pte.mmu_seq = vcpu->kvm->mmu_notifier_seq; - /* implicit mb(), we'll read before PT lock is unlocked */ + smp_rmb(); pfn = gfn_to_pfn(vcpu->kvm, gfn); - up_read(¤t->mm->mmap_sem); if (is_error_pfn(pfn)) { kvm_release_pfn_clean(pfn); Index: kvm/arch/x86/kvm/paging_tmpl.h =================================================================== --- kvm.orig/arch/x86/kvm/paging_tmpl.h +++ kvm/arch/x86/kvm/paging_tmpl.h @@ -102,14 +102,10 @@ static bool FNAME(cmpxchg_gpte)(struct k pt_element_t *table; struct page *page; - down_read(¤t->mm->mmap_sem); page = gfn_to_page(kvm, table_gfn); - up_read(¤t->mm->mmap_sem); table = kmap_atomic(page, KM_USER0); - ret = CMPXCHG(&table[index], orig_pte, new_pte); - kunmap_atomic(table, KM_USER0); kvm_release_page_dirty(page); @@ -418,7 +414,6 @@ static int FNAME(page_fault)(struct kvm_ return 0; } - down_read(¤t->mm->mmap_sem); if (walker.level == PT_DIRECTORY_LEVEL) { gfn_t large_gfn; large_gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE-1); @@ -428,9 +423,8 @@ static int FNAME(page_fault)(struct kvm_ } } mmu_seq = vcpu->kvm->mmu_notifier_seq; - /* implicit mb(), we'll read before PT lock is unlocked */ + smp_rmb(); pfn = gfn_to_pfn(vcpu->kvm, walker.gfn); - up_read(¤t->mm->mmap_sem); /* mmio */ if (is_error_pfn(pfn)) { Index: kvm/arch/x86/kvm/vmx.c =================================================================== --- kvm.orig/arch/x86/kvm/vmx.c +++ kvm/arch/x86/kvm/vmx.c @@ -2010,9 +2010,7 @@ static int alloc_apic_access_page(struct if (r) goto out; - down_read(¤t->mm->mmap_sem); kvm->arch.apic_access_page = gfn_to_page(kvm, 0xfee00); - up_read(¤t->mm->mmap_sem); out: up_write(&kvm->slots_lock); return r; @@ -2034,10 +2032,8 @@ static int alloc_identity_pagetable(stru if (r) goto out; - down_read(¤t->mm->mmap_sem); kvm->arch.ept_identity_pagetable = gfn_to_page(kvm, VMX_EPT_IDENTITY_PAGETABLE_ADDR >> PAGE_SHIFT); - up_read(¤t->mm->mmap_sem); out: up_write(&kvm->slots_lock); return r; Index: kvm/arch/x86/kvm/x86.c =================================================================== --- kvm.orig/arch/x86/kvm/x86.c +++ kvm/arch/x86/kvm/x86.c @@ -931,10 +931,8 @@ int kvm_set_msr_common(struct kvm_vcpu * /* ...but clean it before doing the actual write */ vcpu->arch.time_offset = data & ~(PAGE_MASK | 1); - down_read(¤t->mm->mmap_sem); vcpu->arch.time_page = gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT); - up_read(¤t->mm->mmap_sem); if (is_error_page(vcpu->arch.time_page)) { kvm_release_page_clean(vcpu->arch.time_page); @@ -2303,9 +2301,7 @@ static int emulator_cmpxchg_emulated(uns val = *(u64 *)new; - down_read(¤t->mm->mmap_sem); page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT); - up_read(¤t->mm->mmap_sem); kaddr = kmap_atomic(page, KM_USER0); set_64bit((u64 *)(kaddr + offset_in_page(gpa)), val); @@ -3075,9 +3071,7 @@ static void vapic_enter(struct kvm_vcpu if (!apic || !apic->vapic_addr) return; - down_read(¤t->mm->mmap_sem); page = gfn_to_page(vcpu->kvm, apic->vapic_addr >> PAGE_SHIFT); - up_read(¤t->mm->mmap_sem); vcpu->arch.apic->vapic_page = page; } Index: kvm/virt/kvm/kvm_main.c =================================================================== --- kvm.orig/virt/kvm/kvm_main.c +++ kvm/virt/kvm/kvm_main.c @@ -716,9 +716,6 @@ unsigned long gfn_to_hva(struct kvm *kvm } EXPORT_SYMBOL_GPL(gfn_to_hva); -/* - * Requires current->mm->mmap_sem to be held - */ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn) { struct page *page[1]; @@ -734,20 +731,23 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t return page_to_pfn(bad_page); } - npages = get_user_pages(current, current->mm, addr, 1, 1, 0, page, - NULL); + npages = get_user_pages_fast(addr, 1, 1, page); if (unlikely(npages != 1)) { struct vm_area_struct *vma; + down_read(¤t->mm->mmap_sem); vma = find_vma(current->mm, addr); + if (vma == NULL || addr < vma->vm_start || !(vma->vm_flags & VM_PFNMAP)) { + up_read(¤t->mm->mmap_sem); get_page(bad_page); return page_to_pfn(bad_page); } pfn = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; + up_read(¤t->mm->mmap_sem); BUG_ON(!is_mmio_pfn(pfn)); } else pfn = page_to_pfn(page[0]); @@ -1387,17 +1387,22 @@ out: static int kvm_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf) { + struct page *page[1]; + unsigned long addr; + int npages; + gfn_t gfn = vmf->pgoff; struct kvm *kvm = vma->vm_file->private_data; - struct page *page; - if (!kvm_is_visible_gfn(kvm, vmf->pgoff)) + addr = gfn_to_hva(kvm, gfn); + if (kvm_is_error_hva(addr)) return VM_FAULT_SIGBUS; - page = gfn_to_page(kvm, vmf->pgoff); - if (is_error_page(page)) { - kvm_release_page_clean(page); + + npages = get_user_pages(current, current->mm, addr, 1, 1, 0, page, + NULL); + if (unlikely(npages != 1)) return VM_FAULT_SIGBUS; - } - vmf->page = page; + + vmf->page = page[0]; return 0; } -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html