KVM: MMU: Concurrent guest walkers

Do not hold kvm->lock mutex across the entire pagefault code,
only acquire it in places where it is necessary, such as mmu
hash list, active list, rmap and parent pte handling.

Allow concurrent guest walkers by switching walk_addr() to use
mmap_sem in read-mode.

And get rid of the lockless __gfn_to_page.

[avi: move kvm_mmu_pte_write() locking inside the function]
[avi: add locking for real mode]
[avi: fix cmpxchg locking]

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

1 files changed, 55 insertions, 37 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1f48ec871035..e3b3141db13c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -181,7 +181,7 @@ int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3)
         int ret;
         u64 pdpte[ARRAY_SIZE(vcpu->arch.pdptrs)];
 
-        mutex_lock(&vcpu->kvm->lock);
+        down_read(&current->mm->mmap_sem);
         ret = kvm_read_guest_page(vcpu->kvm, pdpt_gfn, pdpte,
                                   offset * sizeof(u64), sizeof(pdpte));
         if (ret < 0) {
@@ -198,7 +198,7 @@ int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3)
 
         memcpy(vcpu->arch.pdptrs, pdpte, sizeof(vcpu->arch.pdptrs));
 out:
-        mutex_unlock(&vcpu->kvm->lock);
+        up_read(&current->mm->mmap_sem);
 
         return ret;
 }
@@ -212,13 +212,13 @@ static bool pdptrs_changed(struct kvm_vcpu *vcpu)
         if (is_long_mode(vcpu) || !is_pae(vcpu))
                 return false;
 
-        mutex_lock(&vcpu->kvm->lock);
+        down_read(&current->mm->mmap_sem);
         r = kvm_read_guest(vcpu->kvm, vcpu->arch.cr3 & ~31u, pdpte, sizeof(pdpte));
         if (r < 0)
                 goto out;
         changed = memcmp(pdpte, vcpu->arch.pdptrs, sizeof(pdpte)) != 0;
 out:
-        mutex_unlock(&vcpu->kvm->lock);
+        up_read(&current->mm->mmap_sem);
 
         return changed;
 }
@@ -278,9 +278,7 @@ void set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
         kvm_x86_ops->set_cr0(vcpu, cr0);
         vcpu->arch.cr0 = cr0;
 
-        mutex_lock(&vcpu->kvm->lock);
         kvm_mmu_reset_context(vcpu);
-        mutex_unlock(&vcpu->kvm->lock);
         return;
 }
 EXPORT_SYMBOL_GPL(set_cr0);
@@ -320,9 +318,7 @@ void set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
         }
         kvm_x86_ops->set_cr4(vcpu, cr4);
         vcpu->arch.cr4 = cr4;
-        mutex_lock(&vcpu->kvm->lock);
         kvm_mmu_reset_context(vcpu);
-        mutex_unlock(&vcpu->kvm->lock);
 }
 EXPORT_SYMBOL_GPL(set_cr4);
 
@@ -360,7 +356,7 @@ void set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
                  */
         }
 
-        mutex_lock(&vcpu->kvm->lock);
+        down_read(&current->mm->mmap_sem);
         /*
          * Does the new cr3 value map to physical memory? (Note, we
          * catch an invalid cr3 even in real-mode, because it would
@@ -376,7 +372,7 @@ void set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
                 vcpu->arch.cr3 = cr3;
                 vcpu->arch.mmu.new_cr3(vcpu);
         }
-        mutex_unlock(&vcpu->kvm->lock);
+        up_read(&current->mm->mmap_sem);
 }
 EXPORT_SYMBOL_GPL(set_cr3);
 
@@ -1211,12 +1207,12 @@ static int kvm_vm_ioctl_set_nr_mmu_pages(struct kvm *kvm,
         if (kvm_nr_mmu_pages < KVM_MIN_ALLOC_MMU_PAGES)
                 return -EINVAL;
 
-        mutex_lock(&kvm->lock);
+        down_write(&current->mm->mmap_sem);
 
         kvm_mmu_change_mmu_pages(kvm, kvm_nr_mmu_pages);
         kvm->arch.n_requested_mmu_pages = kvm_nr_mmu_pages;
 
-        mutex_unlock(&kvm->lock);
+        up_write(&current->mm->mmap_sem);
         return 0;
 }
 
@@ -1265,7 +1261,7 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
             < alias->target_phys_addr)
                 goto out;
 
-        mutex_lock(&kvm->lock);
+        down_write(&current->mm->mmap_sem);
 
         p = &kvm->arch.aliases[alias->slot];
         p->base_gfn = alias->guest_phys_addr >> PAGE_SHIFT;
@@ -1279,7 +1275,7 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
 
         kvm_mmu_zap_all(kvm);
 
-        mutex_unlock(&kvm->lock);
+        up_write(&current->mm->mmap_sem);
 
         return 0;
 
@@ -1355,7 +1351,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
         struct kvm_memory_slot *memslot;
         int is_dirty = 0;
 
-        mutex_lock(&kvm->lock);
+        down_write(&current->mm->mmap_sem);
 
         r = kvm_get_dirty_log(kvm, log, &is_dirty);
         if (r)
@@ -1371,7 +1367,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
         }
         r = 0;
 out:
-        mutex_unlock(&kvm->lock);
+        up_write(&current->mm->mmap_sem);
         return r;
 }
 
@@ -1565,25 +1561,32 @@ int emulator_read_std(unsigned long addr,
                              struct kvm_vcpu *vcpu)
 {
         void *data = val;
+        int r = X86EMUL_CONTINUE;
 
+        down_read(&current->mm->mmap_sem);
         while (bytes) {
                 gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
                 unsigned offset = addr & (PAGE_SIZE-1);
                 unsigned tocopy = min(bytes, (unsigned)PAGE_SIZE - offset);
                 int ret;
 
-                if (gpa == UNMAPPED_GVA)
-                        return X86EMUL_PROPAGATE_FAULT;
+                if (gpa == UNMAPPED_GVA) {
+                        r = X86EMUL_PROPAGATE_FAULT;
+                        goto out;
+                }
                 ret = kvm_read_guest(vcpu->kvm, gpa, data, tocopy);
-                if (ret < 0)
-                        return X86EMUL_UNHANDLEABLE;
+                if (ret < 0) {
+                        r = X86EMUL_UNHANDLEABLE;
+                        goto out;
+                }
 
                 bytes -= tocopy;
                 data += tocopy;
                 addr += tocopy;
         }
-
-        return X86EMUL_CONTINUE;
+out:
+        up_read(&current->mm->mmap_sem);
+        return r;
 }
 EXPORT_SYMBOL_GPL(emulator_read_std);
 
@@ -1601,7 +1604,9 @@ static int emulator_read_emulated(unsigned long addr,
                 return X86EMUL_CONTINUE;
         }
 
+        down_read(&current->mm->mmap_sem);
         gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+        up_read(&current->mm->mmap_sem);
 
         /* For APIC access vmexit */
         if ((gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
@@ -1617,11 +1622,14 @@ mmio:
         /*
          * Is this MMIO handled locally?
          */
+        mutex_lock(&vcpu->kvm->lock);
         mmio_dev = vcpu_find_mmio_dev(vcpu, gpa);
         if (mmio_dev) {
                 kvm_iodevice_read(mmio_dev, gpa, bytes, val);
+                mutex_unlock(&vcpu->kvm->lock);
                 return X86EMUL_CONTINUE;
         }
+        mutex_unlock(&vcpu->kvm->lock);
 
         vcpu->mmio_needed = 1;
         vcpu->mmio_phys_addr = gpa;
@@ -1636,10 +1644,14 @@ static int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
 {
         int ret;
 
+        down_read(&current->mm->mmap_sem);
         ret = kvm_write_guest(vcpu->kvm, gpa, val, bytes);
-        if (ret < 0)
+        if (ret < 0) {
+                up_read(&current->mm->mmap_sem);
                 return 0;
+        }
         kvm_mmu_pte_write(vcpu, gpa, val, bytes);
+        up_read(&current->mm->mmap_sem);
         return 1;
 }
 
@@ -1649,7 +1661,11 @@ static int emulator_write_emulated_onepage(unsigned long addr,
                                            struct kvm_vcpu *vcpu)
 {
         struct kvm_io_device *mmio_dev;
-        gpa_t                 gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+        gpa_t                 gpa;
+
+        down_read(&current->mm->mmap_sem);
+        gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+        up_read(&current->mm->mmap_sem);
 
         if (gpa == UNMAPPED_GVA) {
                 kvm_inject_page_fault(vcpu, addr, 2);
@@ -1667,11 +1683,14 @@ mmio:
         /*
          * Is this MMIO handled locally?
          */
+        mutex_lock(&vcpu->kvm->lock);
         mmio_dev = vcpu_find_mmio_dev(vcpu, gpa);
         if (mmio_dev) {
                 kvm_iodevice_write(mmio_dev, gpa, bytes, val);
+                mutex_unlock(&vcpu->kvm->lock);
                 return X86EMUL_CONTINUE;
         }
+        mutex_unlock(&vcpu->kvm->lock);
 
         vcpu->mmio_needed = 1;
         vcpu->mmio_phys_addr = gpa;
@@ -1718,11 +1737,14 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
 #ifndef CONFIG_X86_64
         /* guests cmpxchg8b have to be emulated atomically */
         if (bytes == 8) {
-                gpa_t gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+                gpa_t gpa;
                 struct page *page;
                 char *addr;
                 u64 val;
 
+                down_read(&current->mm->mmap_sem);
+                gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, addr);
+
                 if (gpa == UNMAPPED_GVA ||
                    (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
                         goto emul_write;
@@ -1736,8 +1758,9 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
                 set_64bit((u64 *)(addr + offset_in_page(gpa)), val);
                 kunmap_atomic(addr, KM_USER0);
                 kvm_release_page_dirty(page);
+        emul_write:
+                up_read(&current->mm->mmap_sem);
         }
-emul_write:
 #endif
 
         return emulator_write_emulated(addr, new, bytes, vcpu);
@@ -2118,10 +2141,10 @@ int kvm_emulate_pio_string(struct kvm_vcpu *vcpu, struct kvm_run *run, int in,
                 kvm_x86_ops->skip_emulated_instruction(vcpu);
 
         for (i = 0; i < nr_pages; ++i) {
-                mutex_lock(&vcpu->kvm->lock);
+                down_read(&current->mm->mmap_sem);
                 page = gva_to_page(vcpu, address + i * PAGE_SIZE);
                 vcpu->arch.pio.guest_pages[i] = page;
-                mutex_unlock(&vcpu->kvm->lock);
+                up_read(&current->mm->mmap_sem);
                 if (!page) {
                         kvm_inject_gp(vcpu, 0);
                         free_pio_guest_pages(vcpu);
@@ -2247,7 +2270,6 @@ int kvm_fix_hypercall(struct kvm_vcpu *vcpu)
         char instruction[3];
         int ret = 0;
 
-        mutex_lock(&vcpu->kvm->lock);
 
         /*
          * Blow out the MMU to ensure that no other VCPU has an active mapping
@@ -2262,8 +2284,6 @@ int kvm_fix_hypercall(struct kvm_vcpu *vcpu)
             != X86EMUL_CONTINUE)
                 ret = -EFAULT;
 
-        mutex_unlock(&vcpu->kvm->lock);
-
         return ret;
 }
 
@@ -2447,8 +2467,10 @@ 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);
         vcpu->arch.apic->vapic_page = page;
+        up_read(&current->mm->mmap_sem);
 }
 
 static void vapic_exit(struct kvm_vcpu *vcpu)
@@ -2910,13 +2932,13 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
         gpa_t gpa;
 
         vcpu_load(vcpu);
-        mutex_lock(&vcpu->kvm->lock);
+        down_read(&current->mm->mmap_sem);
         gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, vaddr);
+        up_read(&current->mm->mmap_sem);
         tr->physical_address = gpa;
         tr->valid = gpa != UNMAPPED_GVA;
         tr->writeable = 1;
         tr->usermode = 0;
-        mutex_unlock(&vcpu->kvm->lock);
         vcpu_put(vcpu);
 
         return 0;
@@ -3185,13 +3207,11 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
          */
         if (!user_alloc) {
                 if (npages && !old.rmap) {
-                        down_write(&current->mm->mmap_sem);
                         memslot->userspace_addr = do_mmap(NULL, 0,
                                                      npages * PAGE_SIZE,
                                                      PROT_READ | PROT_WRITE,
                                                      MAP_SHARED | MAP_ANONYMOUS,
                                                      0);
-                        up_write(&current->mm->mmap_sem);
 
                         if (IS_ERR((void *)memslot->userspace_addr))
                                 return PTR_ERR((void *)memslot->userspace_addr);
@@ -3199,10 +3219,8 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
                         if (!old.user_alloc && old.rmap) {
                                 int ret;
 
-                                down_write(&current->mm->mmap_sem);
                                 ret = do_munmap(current->mm, old.userspace_addr,
                                                 old.npages * PAGE_SIZE);
-                                up_write(&current->mm->mmap_sem);
                                 if (ret < 0)
                                         printk(KERN_WARNING
                                        "kvm_vm_ioctl_set_memory_region: "