[PATCH v6 4/4] add 2nd stage page fault handling during live migration

Mario Smarduch
2014-05-15T18:28:26Z

This patch adds support for handling 2nd stage page faults during migration,
it disables faulting in huge pages, and splits up existing huge pages.

Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
---
arch/arm/kvm/mmu.c | 36 ++++++++++++++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index b939312..10e7bf6 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1002,6 +1002,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
struct vm_area_struct *vma;
pfn_t pfn;
+ bool migration_active;

write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
if (fault_status == FSC_PERM && !write_fault) {
@@ -1053,12 +1054,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
return -EFAULT;

spin_lock(&kvm->mmu_lock);
+
+ /*
+ * Place inside lock to prevent race condition when whole VM is being
+ * write proteced. Prevent race of huge page install when migration is
+ * active.
+ */
+ migration_active = vcpu->kvm->arch.migration_in_progress;
+
if (mmu_notifier_retry(kvm, mmu_seq))
goto out_unlock;
- if (!hugetlb && !force_pte)
+
+ /* When migrating don't spend cycles coalescing huge pages */
+ if (!hugetlb && !force_pte && !migration_active)
hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);

- if (hugetlb) {
+ /* During migration don't install huge pages */
+ if (hugetlb && !migration_active) {
pmd_t new_pmd = pfn_pmd(pfn, PAGE_S2);
new_pmd = pmd_mkhuge(new_pmd);
if (writable) {
@@ -1069,6 +1081,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
} else {
pte_t new_pte = pfn_pte(pfn, PAGE_S2);
+
+ /*
+ * If pmd is mapping a huge page then split it up into
+ * small pages, when doing live migration.
+ */
+ if (migration_active) {
+ pmd_t *pmd;
+ if (hugetlb) {
+ pfn += pte_index(fault_ipa);
+ gfn = fault_ipa >> PAGE_SHIFT;
+ }
+ new_pte = pfn_pte(pfn, PAGE_S2);
+ pmd = stage2_get_pmd(kvm, NULL, fault_ipa);
+ if (pmd && kvm_pmd_huge(*pmd))
+ clear_pmd_entry(kvm, pmd, fault_ipa);
+ }
+
if (writable) {
kvm_set_s2pte_writable(&new_pte);
kvm_set_pfn_dirty(pfn);
@@ -1077,6 +1106,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, false);
}

+ /* Assuming 4k pages, set one bit/page in memslot dirty_bitmap[] */
+ if (writable)
+ mark_page_dirty(kvm, gfn);

out_unlock:
spin_unlock(&kvm->mmu_lock);
--
1.7.9.5