KVM: MMU: Switch to mmu spinlock

Convert the synchronization of the shadow handling to a separate mmu_lock
spinlock.

Also guard fetch() by mmap_sem in read-mode to protect against alias
and memslot changes.

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

5 files changed, 35 insertions, 31 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c0b757be7b99..834698d24595 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -971,16 +971,12 @@ static void nonpaging_new_cr3(struct kvm_vcpu *vcpu)
 {
 }
 
-static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
+static int __nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write,
+                           gfn_t gfn, struct page *page)
 {
         int level = PT32E_ROOT_LEVEL;
         hpa_t table_addr = vcpu->arch.mmu.root_hpa;
         int pt_write = 0;
-        struct page *page;
-
-        down_read(&current->mm->mmap_sem);
-        page = gfn_to_page(vcpu->kvm, gfn);
-        up_read(&current->mm->mmap_sem);
 
         for (; ; level--) {
                 u32 index = PT64_INDEX(v, level);
@@ -1022,9 +1018,17 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, int write, gfn_t gfn)
 {
         int r;
 
-        mutex_lock(&vcpu->kvm->lock);
-        r = __nonpaging_map(vcpu, v, write, gfn);
-        mutex_unlock(&vcpu->kvm->lock);
+        struct page *page;
+
+        down_read(&current->mm->mmap_sem);
+        page = gfn_to_page(vcpu->kvm, gfn);
+
+        spin_lock(&vcpu->kvm->mmu_lock);
+        r = __nonpaging_map(vcpu, v, write, gfn, page);
+        spin_unlock(&vcpu->kvm->mmu_lock);
+
+        up_read(&current->mm->mmap_sem);
+
         return r;
 }
 
@@ -1045,7 +1049,7 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 
         if (!VALID_PAGE(vcpu->arch.mmu.root_hpa))
                 return;
-        mutex_lock(&vcpu->kvm->lock);
+        spin_lock(&vcpu->kvm->mmu_lock);
 #ifdef CONFIG_X86_64
         if (vcpu->arch.mmu.shadow_root_level == PT64_ROOT_LEVEL) {
                 hpa_t root = vcpu->arch.mmu.root_hpa;
@@ -1053,7 +1057,7 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
                 sp = page_header(root);
                 --sp->root_count;
                 vcpu->arch.mmu.root_hpa = INVALID_PAGE;
-                mutex_unlock(&vcpu->kvm->lock);
+                spin_unlock(&vcpu->kvm->mmu_lock);
                 return;
         }
 #endif
@@ -1067,7 +1071,7 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
                 }
                 vcpu->arch.mmu.pae_root[i] = INVALID_PAGE;
         }
-        mutex_unlock(&vcpu->kvm->lock);
+        spin_unlock(&vcpu->kvm->mmu_lock);
         vcpu->arch.mmu.root_hpa = INVALID_PAGE;
 }
 
@@ -1270,9 +1274,9 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu)
         r = mmu_topup_memory_caches(vcpu);
         if (r)
                 goto out;
-        mutex_lock(&vcpu->kvm->lock);
+        spin_lock(&vcpu->kvm->mmu_lock);
         mmu_alloc_roots(vcpu);
-        mutex_unlock(&vcpu->kvm->lock);
+        spin_unlock(&vcpu->kvm->mmu_lock);
         kvm_x86_ops->set_cr3(vcpu, vcpu->arch.mmu.root_hpa);
         kvm_mmu_flush_tlb(vcpu);
 out:
@@ -1408,7 +1412,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 
         pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);
         mmu_guess_page_from_pte_write(vcpu, gpa, new, bytes);
-        mutex_lock(&vcpu->kvm->lock);
+        spin_lock(&vcpu->kvm->mmu_lock);
         ++vcpu->kvm->stat.mmu_pte_write;
         kvm_mmu_audit(vcpu, "pre pte write");
         if (gfn == vcpu->arch.last_pt_write_gfn
@@ -1477,7 +1481,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
                 }
         }
         kvm_mmu_audit(vcpu, "post pte write");
-        mutex_unlock(&vcpu->kvm->lock);
+        spin_unlock(&vcpu->kvm->mmu_lock);
         if (vcpu->arch.update_pte.page) {
                 kvm_release_page_clean(vcpu->arch.update_pte.page);
                 vcpu->arch.update_pte.page = NULL;
@@ -1493,15 +1497,15 @@ int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
         gpa = vcpu->arch.mmu.gva_to_gpa(vcpu, gva);
         up_read(&current->mm->mmap_sem);
 
-        mutex_lock(&vcpu->kvm->lock);
+        spin_lock(&vcpu->kvm->mmu_lock);
         r = kvm_mmu_unprotect_page(vcpu->kvm, gpa >> PAGE_SHIFT);
-        mutex_unlock(&vcpu->kvm->lock);
+        spin_unlock(&vcpu->kvm->mmu_lock);
         return r;
 }
 
 void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
 {
-        mutex_lock(&vcpu->kvm->lock);
+        spin_lock(&vcpu->kvm->mmu_lock);
         while (vcpu->kvm->arch.n_free_mmu_pages < KVM_REFILL_PAGES) {
                 struct kvm_mmu_page *sp;
 
@@ -1510,7 +1514,7 @@ void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
                 kvm_mmu_zap_page(vcpu->kvm, sp);
                 ++vcpu->kvm->stat.mmu_recycled;
         }
-        mutex_unlock(&vcpu->kvm->lock);
+        spin_unlock(&vcpu->kvm->mmu_lock);
 }
 
 int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code)
@@ -1642,10 +1646,10 @@ void kvm_mmu_zap_all(struct kvm *kvm)
 {
         struct kvm_mmu_page *sp, *node;
 
-        mutex_lock(&kvm->lock);
+        spin_lock(&kvm->mmu_lock);
         list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link)
                 kvm_mmu_zap_page(kvm, sp);
-        mutex_unlock(&kvm->lock);
+        spin_unlock(&kvm->mmu_lock);
 
         kvm_flush_remote_tlbs(kvm);
 }
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 3d7846ba26e1..a35b83a4fef2 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -387,7 +387,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
          */
         r = FNAME(walk_addr)(&walker, vcpu, addr, write_fault, user_fault,
                              fetch_fault);
-        up_read(&current->mm->mmap_sem);
 
         /*
          * The page is not mapped by the guest.  Let the guest handle it.
@@ -396,12 +395,13 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
                 pgprintk("%s: guest page fault\n", __FUNCTION__);
                 inject_page_fault(vcpu, addr, walker.error_code);
                 vcpu->arch.last_pt_write_count = 0; /* reset fork detector */
+                up_read(&current->mm->mmap_sem);
                 return 0;
         }
 
         page = gfn_to_page(vcpu->kvm, walker.gfn);
 
-        mutex_lock(&vcpu->kvm->lock);
+        spin_lock(&vcpu->kvm->mmu_lock);
         shadow_pte = FNAME(fetch)(vcpu, addr, &walker, user_fault, write_fault,
                                   &write_pt, page);
         pgprintk("%s: shadow pte %p %llx ptwrite %d\n", __FUNCTION__,
@@ -414,13 +414,15 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
          * mmio: emulate if accessible, otherwise its a guest fault.
          */
         if (shadow_pte && is_io_pte(*shadow_pte)) {
-                mutex_unlock(&vcpu->kvm->lock);
+                spin_unlock(&vcpu->kvm->mmu_lock);
+                up_read(&current->mm->mmap_sem);
                 return 1;
         }
 
         ++vcpu->stat.pf_fixed;
         kvm_mmu_audit(vcpu, "post page fault (fixed)");
-        mutex_unlock(&vcpu->kvm->lock);
+        spin_unlock(&vcpu->kvm->mmu_lock);
+        up_read(&current->mm->mmap_sem);
 
         return write_pt;
 }
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c39493feba46..3d251f894a8d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1477,7 +1477,6 @@ static int alloc_apic_access_page(struct kvm *kvm)
         struct kvm_userspace_memory_region kvm_userspace_mem;
         int r = 0;
 
-        mutex_lock(&kvm->lock);
         down_write(&current->mm->mmap_sem);
         if (kvm->arch.apic_access_page)
                 goto out;
@@ -1491,7 +1490,6 @@ static int alloc_apic_access_page(struct kvm *kvm)
         kvm->arch.apic_access_page = gfn_to_page(kvm, 0xfee00);
 out:
         up_write(&current->mm->mmap_sem);
-        mutex_unlock(&kvm->lock);
         return r;
 }
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a020fb280540..2714068ee8bc 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -104,7 +104,8 @@ struct kvm_memory_slot {
 };
 
 struct kvm {
-        struct mutex lock; /* protects everything except vcpus */
+        struct mutex lock; /* protects the vcpus array and APIC accesses */
+        spinlock_t mmu_lock;
         struct mm_struct *mm; /* userspace tied to this vm */
         int nmemslots;
         struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS +
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8d0b7c16c2f7..3c4fe26096fc 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -165,6 +165,7 @@ static struct kvm *kvm_create_vm(void)
 
         kvm->mm = current->mm;
         atomic_inc(&kvm->mm->mm_count);
+        spin_lock_init(&kvm->mmu_lock);
         kvm_io_bus_init(&kvm->pio_bus);
         mutex_init(&kvm->lock);
         kvm_io_bus_init(&kvm->mmio_bus);
@@ -552,9 +553,7 @@ int kvm_read_guest_atomic(struct kvm *kvm, gpa_t gpa, void *data,
         addr = gfn_to_hva(kvm, gfn);
         if (kvm_is_error_hva(addr))
                 return -EFAULT;
-        pagefault_disable();
         r = __copy_from_user_inatomic(data, (void __user *)addr + offset, len);
-        pagefault_enable();
         if (r)
                 return -EFAULT;
         return 0;