Re: KVM swapping with mmu notifiers

Andrea Arcangeli
2008-01-22T20:03:52Z

This last update will work against mmu-notifiers #v4, this will make
the accessed bitflag in the spte visible to the linux VM so it will
provide an accurate working set detection w/o requiring vmexits.

Signed-off-by: Andrea Arcangeli <andrea-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 4086080..c527d7d 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -18,6 +18,7 @@ config KVM
tristate "Kernel-based Virtual Machine (KVM) support"
depends on ARCH_SUPPORTS_KVM && EXPERIMENTAL
select PREEMPT_NOTIFIERS
+ select MMU_NOTIFIER
select ANON_INODES
---help---
Support hosting fully virtualized guest machines using hardware
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c85b904..adb20de 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -532,6 +532,110 @@ static void rmap_write_protect(struct kvm *kvm, u64 gfn)
kvm_flush_remote_tlbs(kvm);
}

+static void kvm_unmap_spte(struct kvm *kvm, u64 *spte)
+{
+ struct page *page = pfn_to_page((*spte & PT64_BASE_ADDR_MASK) >> PAGE_SHIFT);
+ get_page(page);
+ rmap_remove(kvm, spte);
+ set_shadow_pte(spte, shadow_trap_nonpresent_pte);
+ kvm_flush_remote_tlbs(kvm);
+ __free_page(page);
+}
+
+static void kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp)
+{
+ u64 *spte, *curr_spte;
+
+ spte = rmap_next(kvm, rmapp, NULL);
+ while (spte) {
+ BUG_ON(!(*spte & PT_PRESENT_MASK));
+ rmap_printk("kvm_rmap_unmap_hva: spte %p %llx\n", spte, *spte);
+ curr_spte = spte;
+ spte = rmap_next(kvm, rmapp, spte);
+ kvm_unmap_spte(kvm, curr_spte);
+ }
+}
+
+void kvm_unmap_hva(struct kvm *kvm, unsigned long hva)
+{
+ int i;
+
+ /*
+ * 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.
+ */
+ spin_lock(&kvm->mmu_lock);
+ for (i = 0; i < kvm->nmemslots; i++) {
+ struct kvm_memory_slot *memslot = &kvm->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;
+ kvm_unmap_rmapp(kvm, &memslot->rmap[gfn_offset]);
+ }
+ }
+ spin_unlock(&kvm->mmu_lock);
+}
+
+static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp)
+{
+ u64 *spte;
+ int young = 0;
+
+ spte = rmap_next(kvm, rmapp, NULL);
+ while (spte) {
+ int _young;
+ u64 _spte = *spte;
+ BUG_ON(!(_spte & PT_PRESENT_MASK));
+ _young = _spte & PT_ACCESSED_MASK;
+ if (_young) {
+ young = !!_young;
+ set_shadow_pte(spte, _spte & ~PT_ACCESSED_MASK);
+ }
+ spte = rmap_next(kvm, rmapp, spte);
+ }
+ return young;
+}
+
+int kvm_age_hva(struct kvm *kvm, unsigned long hva)
+{
+ int i;
+ int young = 0;
+
+ /*
+ * 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.
+ */
+ spin_lock(&kvm->mmu_lock);
+ for (i = 0; i < kvm->nmemslots; i++) {
+ struct kvm_memory_slot *memslot = &kvm->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;
+ young |= kvm_age_rmapp(kvm, &memslot->rmap[gfn_offset]);
+ }
+ }
+ spin_unlock(&kvm->mmu_lock);
+
+ if (young)
+ kvm_flush_remote_tlbs(kvm);
+
+ return young;
+}
+
#ifdef MMU_DEBUG
static int is_empty_shadow_page(u64 *spt)
{
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8f94a0b..35bb114 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3167,6 +3167,43 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
free_page((unsigned long)vcpu->arch.pio_data);
}

+static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)
+{
+ return container_of(mn, struct kvm, mmu_notifier);
+}
+
+void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long address)
+{
+ struct kvm *kvm = mmu_notifier_to_kvm(mn);
+ BUG_ON(mm != kvm->mm);
+ kvm_unmap_hva(kvm, address);
+}
+
+void kvm_mmu_notifier_invalidate_range(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ for (; start < end; start += PAGE_SIZE)
+ kvm_mmu_notifier_invalidate_page(mn, mm, start);
+}
+
+int kvm_mmu_notifier_age_page(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long address)
+{
+ struct kvm *kvm = mmu_notifier_to_kvm(mn);
+ BUG_ON(mm != kvm->mm);
+ return kvm_age_hva(kvm, address);
+}
+
+static const struct mmu_notifier_ops kvm_mmu_notifier_ops = {
+ .invalidate_range = kvm_mmu_notifier_invalidate_range,
+ .invalidate_page = kvm_mmu_notifier_invalidate_page,
+ .age_page = kvm_mmu_notifier_age_page,
+};
+
struct kvm *kvm_arch_create_vm(void)
{
struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
@@ -3175,6 +3212,7 @@ struct kvm *kvm_arch_create_vm(void)
return ERR_PTR(-ENOMEM);

INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);
+ kvm->mmu_notifier.ops = &kvm_mmu_notifier_ops;

return kvm;
}
diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index d6db0de..18496e0 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -404,6 +404,8 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu);
int kvm_mmu_setup(struct kvm_vcpu *vcpu);
void kvm_mmu_set_nonpresent_ptes(u64 trap_pte, u64 notrap_pte);

+void kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
+int kvm_age_hva(struct kvm *kvm, unsigned long hva);
int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
void kvm_mmu_zap_all(struct kvm *kvm);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ea4764b..51c9bb8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -118,6 +118,7 @@ struct kvm {
struct kvm_io_bus pio_bus;
struct kvm_vm_stat stat;
struct kvm_arch arch;
+ struct mmu_notifier mmu_notifier;
};

/* The guest did something we don't support. */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4295623..b5454d1 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);
+ mmu_notifier_register(&kvm->mmu_notifier, kvm->mm);
spin_lock_init(&kvm->mmu_lock);
kvm_io_bus_init(&kvm->pio_bus);
mutex_init(&kvm->lock);