KVM: switch to get_user_pages_fast

Convert gfn_to_pfn to use get_user_pages_fast, which can do lockless
pagetable lookups on x86. Kernel compilation on 4-way guest is 3.7%
faster on VMX.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

4 files changed, 10 insertions, 31 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index bce3e25ec79b..5779a2323e23 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -405,16 +405,19 @@ static int host_largepage_backed(struct kvm *kvm, gfn_t gfn)
 {
         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(&current->mm->mmap_sem);
         vma = find_vma(current->mm, addr);
         if (vma && is_vm_hugetlb_page(vma))
-                return 1;
+                ret = 1;
+        up_read(&current->mm->mmap_sem);
 
-        return 0;
+        return ret;
 }
 
 static int is_largepage_backed(struct kvm_vcpu *vcpu, gfn_t large_gfn)
@@ -1140,9 +1143,7 @@ struct page *gva_to_page(struct kvm_vcpu *vcpu, gva_t gva)
         if (gpa == UNMAPPED_GVA)
                 return NULL;
 
-        down_read(&current->mm->mmap_sem);
         page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
-        up_read(&current->mm->mmap_sem);
 
         return page;
 }
@@ -1330,16 +1331,14 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
         pfn_t pfn;
         unsigned long mmu_seq;
 
-        down_read(&current->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(&current->mm->mmap_sem);
 
         /* mmio */
         if (is_error_pfn(pfn)) {
@@ -1488,15 +1487,13 @@ static int tdp_page_fault(struct kvm_vcpu *vcpu, gva_t gpa,
         if (r)
                 return r;
 
-        down_read(&current->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(&current->mm->mmap_sem);
         if (is_error_pfn(pfn)) {
                 kvm_release_pfn_clean(pfn);
                 return 1;
@@ -1809,15 +1806,13 @@ static void mmu_guess_page_from_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
                 return;
         gfn = (gpte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT;
 
-        down_read(&current->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(&current->mm->mmap_sem);
 
         if (is_error_pfn(pfn)) {
                 kvm_release_pfn_clean(pfn);
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index b671f61be41e..6dd08e096e24 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -102,14 +102,10 @@ static bool FNAME(cmpxchg_gpte)(struct kvm *kvm,
         pt_element_t *table;
         struct page *page;
 
-        down_read(&current->mm->mmap_sem);
         page = gfn_to_page(kvm, table_gfn);
-        up_read(&current->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_vcpu *vcpu, gva_t addr,
                 return 0;
         }
 
-        down_read(&current->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_vcpu *vcpu, gva_t addr,
                 }
         }
         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(&current->mm->mmap_sem);
 
         /* mmio */
         if (is_error_pfn(pfn)) {
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 046a91b5a4ba..025bf4011abc 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2010,9 +2010,7 @@ static int alloc_apic_access_page(struct kvm *kvm)
         if (r)
                 goto out;
 
-        down_read(&current->mm->mmap_sem);
         kvm->arch.apic_access_page = gfn_to_page(kvm, 0xfee00);
-        up_read(&current->mm->mmap_sem);
 out:
         up_write(&kvm->slots_lock);
         return r;
@@ -2034,10 +2032,8 @@ static int alloc_identity_pagetable(struct kvm *kvm)
         if (r)
                 goto out;
 
-        down_read(&current->mm->mmap_sem);
         kvm->arch.ept_identity_pagetable = gfn_to_page(kvm,
                         VMX_EPT_IDENTITY_PAGETABLE_ADDR >> PAGE_SHIFT);
-        up_read(&current->mm->mmap_sem);
 out:
         up_write(&kvm->slots_lock);
         return r;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 61eddbeabeb4..108f07267e87 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -946,10 +946,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
                 /* ...but clean it before doing the actual write */
                 vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
 
-                down_read(&current->mm->mmap_sem);
                 vcpu->arch.time_page =
                                 gfn_to_page(vcpu->kvm, data >> PAGE_SHIFT);
-                up_read(&current->mm->mmap_sem);
 
                 if (is_error_page(vcpu->arch.time_page)) {
                         kvm_release_page_clean(vcpu->arch.time_page);
@@ -2322,9 +2320,7 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
 
                 val = *(u64 *)new;
 
-                down_read(&current->mm->mmap_sem);
                 page = gfn_to_page(vcpu->kvm, gpa >> PAGE_SHIFT);
-                up_read(&current->mm->mmap_sem);
 
                 kaddr = kmap_atomic(page, KM_USER0);
                 set_64bit((u64 *)(kaddr + offset_in_page(gpa)), val);
@@ -3089,9 +3085,7 @@ static void vapic_enter(struct kvm_vcpu *vcpu)
         if (!apic || !apic->vapic_addr)
                 return;
 
-        down_read(&current->mm->mmap_sem);
         page = gfn_to_page(vcpu->kvm, apic->vapic_addr >> PAGE_SHIFT);
-        up_read(&current->mm->mmap_sem);
 
         vcpu->arch.apic->vapic_page = page;
 }