swapping with MMU Notifiers V2

Andrea Arcangeli
2008-01-29T14:50:21Z

Hello,

I'm testing KVM swapping on top of Christoph's latest patch
series. However the host is hanging hard for me. Could others test it?
I changed test-hardware, kernel version and kvm kernel version at the
same time, so it might not be an issue with MMU Notifiers V2 but
something else with my new test-setup (previously I was developing and
testing on my workstation which was by far not ideal).

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 635e70c..80ebc19 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -524,6 +524,110 @@ 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..8954836 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3167,6 +3167,44 @@ 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,
+ int lock)
+{
+ 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 +3213,7 @@ 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 67ae307..14733f2 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..9349160 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -15,6 +15,7 @@
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/preempt.h>
+#include <linux/mmu_notifier.h>
#include <asm/signal.h>

#include <linux/kvm.h>
@@ -118,6 +119,7 @@ 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 8fc12dc..bb4747c 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);
@@ -1265,7 +1266,11 @@ static int kvm_resume(struct sys_device *dev)
}

static struct sysdev_class kvm_sysdev_class = {
+#ifdef set_kset_name
set_kset_name("kvm"),
+#else
+ .name = "kvm",
+#endif
.suspend = kvm_suspend,
.resume = kvm_resume,
};

You also need the locking patch:

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

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8a90403..35a2ee0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3219,14 +3249,20 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
*/
if (!user_alloc) {
if (npages && !old.rmap) {
- memslot->userspace_addr = do_mmap(NULL, 0,
- npages * PAGE_SIZE,
- PROT_READ | PROT_WRITE,
- MAP_SHARED | MAP_ANONYMOUS,
- 0);
-
- if (IS_ERR((void *)memslot->userspace_addr))
- return PTR_ERR((void *)memslot->userspace_addr);
+ unsigned long userspace_addr;
+
+ userspace_addr = do_mmap(NULL, 0,
+ npages * PAGE_SIZE,
+ PROT_READ | PROT_WRITE,
+ MAP_SHARED | MAP_ANONYMOUS,
+ 0);
+ if (IS_ERR((void *)userspace_addr))
+ return PTR_ERR((void *)userspace_addr);
+
+ /* set userspace_addr atomically for kvm_hva_to_rmapp */
+ spin_lock(&kvm->mmu_lock);
+ memslot->userspace_addr = userspace_addr;
+ spin_unlock(&kvm->mmu_lock);
} else {
if (!old.user_alloc && old.rmap) {
int ret;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4295623..a67e38f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -298,7 +299,15 @@ int __kvm_set_memory_region(struct kvm *kvm,
memset(new.rmap, 0, npages * sizeof(*new.rmap));

new.user_alloc = user_alloc;
- new.userspace_addr = mem->userspace_addr;
+ /*
+ * 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;
}

/* Allocate page dirty bitmap if needed */
@@ -311,14 +320,18 @@ int __kvm_set_memory_region(struct kvm *kvm,
memset(new.dirty_bitmap, 0, dirty_bytes);
}

+ spin_lock(&kvm->mmu_lock);
if (mem->slot >= kvm->nmemslots)
kvm->nmemslots = mem->slot + 1;

*memslot = new;
+ spin_unlock(&kvm->mmu_lock);

r = kvm_arch_set_memory_region(kvm, mem, old, user_alloc);
if (r) {
+ spin_lock(&kvm->mmu_lock);
*memslot = old;
+ spin_unlock(&kvm->mmu_lock);
goto out_free;
}

This is the updated compatibility code:

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

diff --git a/kernel/external-module-compat.h b/kernel/external-module-compat.h
index 67b9cc4..6d2be6a 100644
--- a/kernel/external-module-compat.h
+++ b/kernel/external-module-compat.h
@@ -17,6 +17,45 @@
#include <linux/hrtimer.h>
#include <asm/bitops.h>

+#ifndef CONFIG_MMU_NOTIFIER
+struct mmu_notifier;
+
+struct mmu_notifier_ops {
+ /*
+ * Note: The mmu_notifier structure must be released with
+ * call_rcu() since other processors are only guaranteed to
+ * see the changes after a quiescent period.
+ */
+ void (*release)(struct mmu_notifier *mn,
+ struct mm_struct *mm);
+
+ int (*age_page)(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long address);
+
+ void (*invalidate_page)(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long address);
+
+ /* Dummy needed because the mmu_notifier() macro requires it */
+ void (*invalidate_all)(struct mmu_notifier *mn, struct mm_struct *mm,
+ int dummy);
+
+ /*
+ * lock indicates that the function is called under spinlock.
+ */
+ void (*invalidate_range)(struct mmu_notifier *mn,
+ struct mm_struct *mm,
+ unsigned long start, unsigned long end,
+ int lock);
+};
+
+struct mmu_notifier {
+ const struct mmu_notifier_ops *ops;
+};
+#define mmu_notifier_register(mn, mm) do {} while(0)
+#endif
+
/*
* 2.6.16 does not have GFP_NOWAIT
*/

This is the patch to apply on top of V2 fix the aging:

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

diff --git a/mm/rmap.c b/mm/rmap.c
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -285,10 +285,8 @@ static int page_referenced_one(struct pa
if (!pte)
goto out;

- if (ptep_clear_flush_young(vma, address, pte))
- referenced++;
-
- if (mmu_notifier_age_page(mm, address))
+ if (ptep_clear_flush_young(vma, address, pte) |
+ mmu_notifier_age_page(mm, address))
referenced++;

/* Pretend the page is referenced if the task has the
@@ -684,7 +682,7 @@ static int try_to_unmap_one(struct page
* skipped over this mm) then we should reactivate it.
*/
if (!migration && ((vma->vm_flags & VM_LOCKED) ||
- (ptep_clear_flush_young(vma, address, pte) ||
+ (ptep_clear_flush_young(vma, address, pte) |
mmu_notifier_age_page(mm, address)))) {
ret = SWAP_FAIL;
goto out_unmap;
@@ -818,10 +816,8 @@ static void try_to_unmap_cluster(unsigne
page = vm_normal_page(vma, address, *pte);
BUG_ON(!page || PageAnon(page));

- if (ptep_clear_flush_young(vma, address, pte))
- continue;
-
- if (mmu_notifier_age_page(mm, address))
+ if (ptep_clear_flush_young(vma, address, pte) |
+ mmu_notifier_age_page(mm, address))
continue;

/* Nuke the page table entry. */