KVM: introduce kvm->srcu and convert kvm_set_memory_region to SRCU update

Use two steps for memslot deletion: mark the slot invalid (which stops
instantiation of new shadow pages for that slot, but allows destruction),
then instantiate the new empty slot.

Also simplifies kvm_handle_hva locking.

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

8 files changed, 136 insertions, 64 deletions

diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 0757c7027986..b2e4d16dd39e 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1382,7 +1382,7 @@ static void kvm_release_vm_pages(struct kvm *kvm)
         int i, j;
         unsigned long base_gfn;
 
-        slots = kvm->memslots;
+        slots = rcu_dereference(kvm->memslots);
         for (i = 0; i < slots->nmemslots; i++) {
                 memslot = &slots->memslots[i];
                 base_gfn = memslot->base_gfn;
@@ -1837,6 +1837,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
         struct kvm_memory_slot *memslot;
         int is_dirty = 0;
 
+        down_write(&kvm->slots_lock);
         spin_lock(&kvm->arch.dirty_log_lock);
 
         r = kvm_ia64_sync_dirty_log(kvm, log);
@@ -1856,6 +1857,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
         }
         r = 0;
 out:
+        up_write(&kvm->slots_lock);
         spin_unlock(&kvm->arch.dirty_log_lock);
         return r;
 }
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 81f84d326a84..f8bf42a25995 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -29,6 +29,7 @@
 #include <linux/swap.h>
 #include <linux/hugetlb.h>
 #include <linux/compiler.h>
+#include <linux/srcu.h>
 
 #include <asm/page.h>
 #include <asm/cmpxchg.h>
@@ -807,21 +808,15 @@ static int kvm_handle_hva(struct kvm *kvm, unsigned long hva,
 {
         int i, j;
         int retval = 0;
-        struct kvm_memslots *slots = kvm->memslots;
+        struct kvm_memslots *slots;
+
+        slots = rcu_dereference(kvm->memslots);
 
-        /*
-         * If mmap_sem isn't taken, we can look the memslots with only
-         * the mmu_lock by skipping over the slots with userspace_addr == 0.
-         */
         for (i = 0; i < slots->nmemslots; i++) {
                 struct kvm_memory_slot *memslot = &slots->memslots[i];
                 unsigned long start = memslot->userspace_addr;
                 unsigned long end;
 
-                /* mmu_lock protects userspace_addr */
-                if (!start)
-                        continue;
-
                 end = start + (memslot->npages << PAGE_SHIFT);
                 if (hva >= start && hva < end) {
                         gfn_t gfn_offset = (hva - start) >> PAGE_SHIFT;
@@ -1617,7 +1612,7 @@ static void mmu_unshadow(struct kvm *kvm, gfn_t gfn)
 
 static void page_header_update_slot(struct kvm *kvm, void *pte, gfn_t gfn)
 {
-        int slot = memslot_id(kvm, gfn_to_memslot(kvm, gfn));
+        int slot = memslot_id(kvm, gfn);
         struct kvm_mmu_page *sp = page_header(__pa(pte));
 
         __set_bit(slot, sp->slot_bitmap);
@@ -3021,9 +3016,11 @@ unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm)
         int i;
         unsigned int nr_mmu_pages;
         unsigned int  nr_pages = 0;
+        struct kvm_memslots *slots;
 
-        for (i = 0; i < kvm->memslots->nmemslots; i++)
-                nr_pages += kvm->memslots->memslots[i].npages;
+        slots = rcu_dereference(kvm->memslots);
+        for (i = 0; i < slots->nmemslots; i++)
+                nr_pages += slots->memslots[i].npages;
 
         nr_mmu_pages = nr_pages * KVM_PERMILLE_MMU_PAGES / 1000;
         nr_mmu_pages = max(nr_mmu_pages,
@@ -3293,10 +3290,12 @@ static void audit_mappings(struct kvm_vcpu *vcpu)
 static int count_rmaps(struct kvm_vcpu *vcpu)
 {
         int nmaps = 0;
-        int i, j, k;
+        int i, j, k, idx;
 
+        idx = srcu_read_lock(&kvm->srcu);
+        slots = rcu_dereference(kvm->memslots);
         for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
-                struct kvm_memory_slot *m = &vcpu->kvm->memslots->memslots[i];
+                struct kvm_memory_slot *m = &slots->memslots[i];
                 struct kvm_rmap_desc *d;
 
                 for (j = 0; j < m->npages; ++j) {
@@ -3319,6 +3318,7 @@ static int count_rmaps(struct kvm_vcpu *vcpu)
                         }
                 }
         }
+        srcu_read_unlock(&kvm->srcu, idx);
         return nmaps;
 }
 
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 18698799e365..f1cae7d6113d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1503,7 +1503,11 @@ static void enter_pmode(struct kvm_vcpu *vcpu)
 static gva_t rmode_tss_base(struct kvm *kvm)
 {
         if (!kvm->arch.tss_addr) {
-                gfn_t base_gfn = kvm->memslots->memslots[0].base_gfn +
+                struct kvm_memslots *slots;
+                gfn_t base_gfn;
+
+                slots = rcu_dereference(kvm->memslots);
+                base_gfn = kvm->memslots->memslots[0].base_gfn +
                                  kvm->memslots->memslots[0].npages - 3;
                 return base_gfn << PAGE_SHIFT;
         }
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index a24de0b1858e..f2feef68ffd6 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -103,7 +103,7 @@ struct kvm_userspace_memory_region {
 
 /* for kvm_memory_region::flags */
 #define KVM_MEM_LOG_DIRTY_PAGES  1UL
-
+#define KVM_MEMSLOT_INVALID      (1UL << 1)
 
 /* for KVM_IRQ_LINE */
 struct kvm_irq_level {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9af240387fe6..93bd30701ca7 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -162,6 +162,7 @@ struct kvm {
         struct rw_semaphore slots_lock;
         struct mm_struct *mm; /* userspace tied to this vm */
         struct kvm_memslots *memslots;
+        struct srcu_struct srcu;
 #ifdef CONFIG_KVM_APIC_ARCHITECTURE
         u32 bsp_vcpu_id;
         struct kvm_vcpu *bsp_vcpu;
@@ -275,6 +276,7 @@ void kvm_set_page_accessed(struct page *page);
 pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn);
 pfn_t gfn_to_pfn_memslot(struct kvm *kvm,
                          struct kvm_memory_slot *slot, gfn_t gfn);
+int memslot_id(struct kvm *kvm, gfn_t gfn);
 void kvm_release_pfn_dirty(pfn_t);
 void kvm_release_pfn_clean(pfn_t pfn);
 void kvm_set_pfn_dirty(pfn_t pfn);
@@ -490,11 +492,6 @@ static inline void kvm_guest_exit(void)
         current->flags &= ~PF_VCPU;
 }
 
-static inline int memslot_id(struct kvm *kvm, struct kvm_memory_slot *slot)
-{
-        return slot - kvm->memslots->memslots;
-}
-
 static inline gpa_t gfn_to_gpa(gfn_t gfn)
 {
         return (gpa_t)gfn << PAGE_SHIFT;
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index f73de631e3ee..f51e684dd238 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -504,12 +504,12 @@ out:
 static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
                                       struct kvm_assigned_pci_dev *assigned_dev)
 {
-        int r = 0;
+        int r = 0, idx;
         struct kvm_assigned_dev_kernel *match;
         struct pci_dev *dev;
 
         mutex_lock(&kvm->lock);
-        down_read(&kvm->slots_lock);
+        idx = srcu_read_lock(&kvm->srcu);
 
         match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
                                       assigned_dev->assigned_dev_id);
@@ -573,7 +573,7 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
         }
 
 out:
-        up_read(&kvm->slots_lock);
+        srcu_read_unlock(&kvm->srcu, idx);
         mutex_unlock(&kvm->lock);
         return r;
 out_list_del:
@@ -585,7 +585,7 @@ out_put:
         pci_dev_put(dev);
 out_free:
         kfree(match);
-        up_read(&kvm->slots_lock);
+        srcu_read_unlock(&kvm->srcu, idx);
         mutex_unlock(&kvm->lock);
         return r;
 }
diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index cf567d8033db..65a51432c8e5 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c
@@ -78,7 +78,7 @@ static int kvm_iommu_map_memslots(struct kvm *kvm)
         int i, r = 0;
         struct kvm_memslots *slots;
 
-        slots = kvm->memslots;
+        slots = rcu_dereference(kvm->memslots);
 
         for (i = 0; i < slots->nmemslots; i++) {
                 r = kvm_iommu_map_pages(kvm, &slots->memslots[i]);
@@ -214,7 +214,7 @@ static int kvm_iommu_unmap_memslots(struct kvm *kvm)
         int i;
         struct kvm_memslots *slots;
 
-        slots = kvm->memslots;
+        slots = rcu_dereference(kvm->memslots);
 
         for (i = 0; i < slots->nmemslots; i++) {
                 kvm_iommu_put_pages(kvm, slots->memslots[i].base_gfn,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 87d296d8b270..2bb24a814fdf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -44,6 +44,7 @@
 #include <linux/bitops.h>
 #include <linux/spinlock.h>
 #include <linux/compat.h>
+#include <linux/srcu.h>
 
 #include <asm/processor.h>
 #include <asm/io.h>
@@ -213,7 +214,7 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
                                              unsigned long address)
 {
         struct kvm *kvm = mmu_notifier_to_kvm(mn);
-        int need_tlb_flush;
+        int need_tlb_flush, idx;
 
         /*
          * When ->invalidate_page runs, the linux pte has been zapped
@@ -233,10 +234,12 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
          * pte after kvm_unmap_hva returned, without noticing the page
          * is going to be freed.
          */
+        idx = srcu_read_lock(&kvm->srcu);
         spin_lock(&kvm->mmu_lock);
         kvm->mmu_notifier_seq++;
         need_tlb_flush = kvm_unmap_hva(kvm, address);
         spin_unlock(&kvm->mmu_lock);
+        srcu_read_unlock(&kvm->srcu, idx);
 
         /* we've to flush the tlb before the pages can be freed */
         if (need_tlb_flush)
@@ -250,11 +253,14 @@ static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
                                         pte_t pte)
 {
         struct kvm *kvm = mmu_notifier_to_kvm(mn);
+        int idx;
 
+        idx = srcu_read_lock(&kvm->srcu);
         spin_lock(&kvm->mmu_lock);
         kvm->mmu_notifier_seq++;
         kvm_set_spte_hva(kvm, address, pte);
         spin_unlock(&kvm->mmu_lock);
+        srcu_read_unlock(&kvm->srcu, idx);
 }
 
 static void kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
@@ -263,8 +269,9 @@ static void kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
                                                     unsigned long end)
 {
         struct kvm *kvm = mmu_notifier_to_kvm(mn);
-        int need_tlb_flush = 0;
+        int need_tlb_flush = 0, idx;
 
+        idx = srcu_read_lock(&kvm->srcu);
         spin_lock(&kvm->mmu_lock);
         /*
          * The count increase must become visible at unlock time as no
@@ -275,6 +282,7 @@ static void kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
         for (; start < end; start += PAGE_SIZE)
                 need_tlb_flush |= kvm_unmap_hva(kvm, start);
         spin_unlock(&kvm->mmu_lock);
+        srcu_read_unlock(&kvm->srcu, idx);
 
         /* we've to flush the tlb before the pages can be freed */
         if (need_tlb_flush)
@@ -312,11 +320,13 @@ static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
                                               unsigned long address)
 {
         struct kvm *kvm = mmu_notifier_to_kvm(mn);
-        int young;
+        int young, idx;
 
+        idx = srcu_read_lock(&kvm->srcu);
         spin_lock(&kvm->mmu_lock);
         young = kvm_age_hva(kvm, address);
         spin_unlock(&kvm->mmu_lock);
+        srcu_read_unlock(&kvm->srcu, idx);
 
         if (young)
                 kvm_flush_remote_tlbs(kvm);
@@ -379,11 +389,15 @@ static struct kvm *kvm_create_vm(void)
         kvm->memslots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
         if (!kvm->memslots)
                 goto out_err;
+        if (init_srcu_struct(&kvm->srcu))
+                goto out_err;
 
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
         page = alloc_page(GFP_KERNEL | __GFP_ZERO);
-        if (!page)
+        if (!page) {
+                cleanup_srcu_struct(&kvm->srcu);
                 goto out_err;
+        }
 
         kvm->coalesced_mmio_ring =
                         (struct kvm_coalesced_mmio_ring *)page_address(page);
@@ -391,6 +405,7 @@ static struct kvm *kvm_create_vm(void)
 
         r = kvm_init_mmu_notifier(kvm);
         if (r) {
+                cleanup_srcu_struct(&kvm->srcu);
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
                 put_page(page);
 #endif
@@ -480,6 +495,7 @@ static void kvm_destroy_vm(struct kvm *kvm)
 #else
         kvm_arch_flush_shadow(kvm);
 #endif
+        cleanup_srcu_struct(&kvm->srcu);
         kvm_arch_destroy_vm(kvm);
         hardware_disable_all();
         mmdrop(mm);
@@ -521,12 +537,13 @@ int __kvm_set_memory_region(struct kvm *kvm,
                             struct kvm_userspace_memory_region *mem,
                             int user_alloc)
 {
-        int r;
+        int r, flush_shadow = 0;
         gfn_t base_gfn;
         unsigned long npages;
         unsigned long i;
         struct kvm_memory_slot *memslot;
         struct kvm_memory_slot old, new;
+        struct kvm_memslots *slots, *old_memslots;
 
         r = -EINVAL;
         /* General sanity checks */
@@ -588,15 +605,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 memset(new.rmap, 0, npages * sizeof(*new.rmap));
 
                 new.user_alloc = user_alloc;
-                /*
-                 * hva_to_rmmap() serialzies with the mmu_lock and to be
-                 * safe it has to ignore memslots with !user_alloc &&
-                 * !userspace_addr.
-                 */
-                if (user_alloc)
-                        new.userspace_addr = mem->userspace_addr;
-                else
-                        new.userspace_addr = 0;
+                new.userspace_addr = mem->userspace_addr;
         }
         if (!npages)
                 goto skip_lpage;
@@ -651,8 +660,9 @@ skip_lpage:
                 if (!new.dirty_bitmap)
                         goto out_free;
                 memset(new.dirty_bitmap, 0, dirty_bytes);
+                /* destroy any largepage mappings for dirty tracking */
                 if (old.npages)
-                        kvm_arch_flush_shadow(kvm);
+                        flush_shadow = 1;
         }
 #else  /* not defined CONFIG_S390 */
         new.user_alloc = user_alloc;
@@ -660,34 +670,72 @@ skip_lpage:
                 new.userspace_addr = mem->userspace_addr;
 #endif /* not defined CONFIG_S390 */
 
-        if (!npages)
+        if (!npages) {
+                r = -ENOMEM;
+                slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
+                if (!slots)
+                        goto out_free;
+                memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
+                if (mem->slot >= slots->nmemslots)
+                        slots->nmemslots = mem->slot + 1;
+                slots->memslots[mem->slot].flags |= KVM_MEMSLOT_INVALID;
+
+                old_memslots = kvm->memslots;
+                rcu_assign_pointer(kvm->memslots, slots);
+                synchronize_srcu_expedited(&kvm->srcu);
+                /* From this point no new shadow pages pointing to a deleted
+                 * memslot will be created.
+                 *
+                 * validation of sp->gfn happens in:
+                 *      - gfn_to_hva (kvm_read_guest, gfn_to_pfn)
+                 *      - kvm_is_visible_gfn (mmu_check_roots)
+                 */
                 kvm_arch_flush_shadow(kvm);
+                kfree(old_memslots);
+        }
 
         r = kvm_arch_prepare_memory_region(kvm, &new, old, mem, user_alloc);
         if (r)
                 goto out_free;
 
-        spin_lock(&kvm->mmu_lock);
-        if (mem->slot >= kvm->memslots->nmemslots)
-                kvm->memslots->nmemslots = mem->slot + 1;
+#ifdef CONFIG_DMAR
+        /* map the pages in iommu page table */
+        if (npages) {
+                r = kvm_iommu_map_pages(kvm, &new);
+                if (r)
+                        goto out_free;
+        }
+#endif
 
-        *memslot = new;
-        spin_unlock(&kvm->mmu_lock);
+        r = -ENOMEM;
+        slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
+        if (!slots)
+                goto out_free;
+        memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
+        if (mem->slot >= slots->nmemslots)
+                slots->nmemslots = mem->slot + 1;
+
+        /* actual memory is freed via old in kvm_free_physmem_slot below */
+        if (!npages) {
+                new.rmap = NULL;
+                new.dirty_bitmap = NULL;
+                for (i = 0; i < KVM_NR_PAGE_SIZES - 1; ++i)
+                        new.lpage_info[i] = NULL;
+        }
+
+        slots->memslots[mem->slot] = new;
+        old_memslots = kvm->memslots;
+        rcu_assign_pointer(kvm->memslots, slots);
+        synchronize_srcu_expedited(&kvm->srcu);
 
         kvm_arch_commit_memory_region(kvm, mem, old, user_alloc);
 
-        kvm_free_physmem_slot(&old, npages ? &new : NULL);
-        /* Slot deletion case: we have to update the current slot */
-        spin_lock(&kvm->mmu_lock);
-        if (!npages)
-                *memslot = old;
-        spin_unlock(&kvm->mmu_lock);
-#ifdef CONFIG_DMAR
-        /* map the pages in iommu page table */
-        r = kvm_iommu_map_pages(kvm, memslot);
-        if (r)
-                goto out;
-#endif
+        kvm_free_physmem_slot(&old, &new);
+        kfree(old_memslots);
+
+        if (flush_shadow)
+                kvm_arch_flush_shadow(kvm);
+
         return 0;
 
 out_free:
@@ -787,7 +835,7 @@ EXPORT_SYMBOL_GPL(kvm_is_error_hva);
 struct kvm_memory_slot *gfn_to_memslot_unaliased(struct kvm *kvm, gfn_t gfn)
 {
         int i;
-        struct kvm_memslots *slots = kvm->memslots;
+        struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
 
         for (i = 0; i < slots->nmemslots; ++i) {
                 struct kvm_memory_slot *memslot = &slots->memslots[i];
@@ -809,12 +857,15 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
 int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 {
         int i;
-        struct kvm_memslots *slots = kvm->memslots;
+        struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
 
         gfn = unalias_gfn(kvm, gfn);
         for (i = 0; i < KVM_MEMORY_SLOTS; ++i) {
                 struct kvm_memory_slot *memslot = &slots->memslots[i];
 
+                if (memslot->flags & KVM_MEMSLOT_INVALID)
+                        continue;
+
                 if (gfn >= memslot->base_gfn
                     && gfn < memslot->base_gfn + memslot->npages)
                         return 1;
@@ -823,13 +874,31 @@ int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);
 
+int memslot_id(struct kvm *kvm, gfn_t gfn)
+{
+        int i;
+        struct kvm_memslots *slots = rcu_dereference(kvm->memslots);
+        struct kvm_memory_slot *memslot = NULL;
+
+        gfn = unalias_gfn(kvm, gfn);
+        for (i = 0; i < slots->nmemslots; ++i) {
+                memslot = &slots->memslots[i];
+
+                if (gfn >= memslot->base_gfn
+                    && gfn < memslot->base_gfn + memslot->npages)
+                        break;
+        }
+
+        return memslot - slots->memslots;
+}
+
 unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 {
         struct kvm_memory_slot *slot;
 
         gfn = unalias_gfn(kvm, gfn);
         slot = gfn_to_memslot_unaliased(kvm, gfn);
-        if (!slot)
+        if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
                 return bad_hva();
         return (slot->userspace_addr + (gfn - slot->base_gfn) * PAGE_SIZE);
 }