[PATCH v3 2/4] live migration support for initial write protect of VM

Mario Smarduch
2014-04-22T23:18:09Z

Support for live migration initial write protect.
- moved write protect to architecture memory region prepare function. This
way you can fail, abort migration without keep track of migration status.
- Above also allows to generalize read dirty log function with x86
- Added stage2_mark_pte_ro()
- optimized initial write protect, skip upper table lookups
- added stage2pmd_addr_end() to do generic 4 level table walk
- changed kvm_flush_remote_tlbs() to weak function

Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
---
arch/arm/include/asm/kvm_host.h | 8 ++
arch/arm/kvm/arm.c | 3 +
arch/arm/kvm/mmu.c | 163 +++++++++++++++++++++++++++++++++++++++
virt/kvm/kvm_main.c | 5 +-
4 files changed, 178 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 1e739f9..9f827c8 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -67,6 +67,12 @@ struct kvm_arch {

/* Interrupt controller */
struct vgic_dist vgic;
+
+ /* Marks start of migration, used to handle 2nd stage page faults
+ * during migration, prevent installing huge pages and split huge pages
+ * to small pages.
+ */
+ int migration_in_progress;
};

#define KVM_NR_MEM_OBJS 40
@@ -230,4 +236,6 @@ int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);

void kvm_tlb_flush_vmid(struct kvm *kvm);

+int kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
+
#endif /* __ARM_KVM_HOST_H__ */
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 9a4bc10..b916478 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -233,6 +233,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
struct kvm_userspace_memory_region *mem,
enum kvm_mr_change change)
{
+ /* Request for migration issued by user, write protect memory slot */
+ if ((change != KVM_MR_DELETE) && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
+ return kvm_mmu_slot_remove_write_access(kvm, mem->slot);
return 0;
}

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 7ab77f3..4d029a6 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -31,6 +31,11 @@

#include "trace.h"

+#define stage2pud_addr_end(addr, end) \
+({ u64 __boundary = ((addr) + PUD_SIZE) & PUD_MASK; \
+ (__boundary - 1 < (end) - 1) ? __boundary : (end); \
+})
+
extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];

static pgd_t *boot_hyp_pgd;
@@ -569,6 +574,15 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
return 0;
}

+/* Write protect page */
+static void stage2_mark_pte_ro(pte_t *pte)
+{
+ pte_t new_pte;
+
+ new_pte = pfn_pte(pte_pfn(*pte), PAGE_S2);
+ *pte = new_pte;
+}
+
/**
* kvm_phys_addr_ioremap - map a device range to guest IPA
*
@@ -649,6 +663,155 @@ static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
return false;
}

+/**
+ * split_pmd - splits huge pages to small pages, required to keep a dirty log of
+ * smaller memory granules, otherwise huge pages would need to be
+ * migrated. Practically an idle system has problems migrating with
+ * huge pages. Called during WP of entire VM address space, done
+ * initially when migration thread isses the KVM_MEM_LOG_DIRTY_PAGES
+ * ioctl.
+ * The mmu_lock is held during splitting.
+ *
+ * @kvm: The KVM pointer
+ * @pmd: Pmd to 2nd stage huge page
+ * @addr: ` Guest Physical Address
+ */
+int split_pmd(struct kvm *kvm, pmd_t *pmd, u64 addr)
+{
+ struct page *page;
+ pfn_t pfn = pmd_pfn(*pmd);
+ pte_t *pte;
+ int i;
+
+ page = alloc_page(GFP_KERNEL);
+ if (page == NULL)
+ return -ENOMEM;
+
+ pte = page_address(page);
+ /* cycle through ptes first, use pmd pfn */
+ for (i = 0; i < PTRS_PER_PMD; i++) {
+ pte[i] = pfn_pte(pfn+i, 0);
+ stage2_mark_pte_ro(&pte[i]);
+ }
+ kvm_clean_pte(pte);
+ /* After page table setup set pmd */
+ pmd_populate_kernel(NULL, pmd, pte);
+
+ /* get reference on pte page */
+ get_page(virt_to_page(pte));
+ return 0;
+}
+
+/**
+ * kvm_mmu_slot_remove_access - write protects entire VM address space.
+ * Called at start of migration when KVM_MEM_LOG_DIRTY_PAGES ioctl is
+ * issued. After this function returns all pages (minus the ones faulted
+ * in when mmu_lock is released) must be write protected to keep track of
+ * dirty pages to migrate on subsequent dirty log retrieval.
+ * mmu_lock is held during write protecting, released on contention.
+ *
+ * @kvm: The KVM pointer
+ * @slot: The memory slot the dirty log is retrieved for
+ */
+int kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
+{
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+ pgd_t *pgdp = kvm->arch.pgd;
+ struct kvm_memory_slot *memslot = id_to_memslot(kvm->memslots, slot);
+ u64 start = memslot->base_gfn << PAGE_SHIFT;
+ u64 end = (memslot->base_gfn + memslot->npages) << PAGE_SHIFT;
+ u64 addr = start;
+ u64 pgdir_end, pud_end, pmd_end;
+ int ret;
+
+ spin_lock(&kvm->mmu_lock);
+ /* set start of migration, sychronize with Data Abort handler */
+ kvm->arch.migration_in_progress = 1;
+
+ /* Walk range, split up huge pages as needed and write protect ptes */
+ while (addr < end) {
+ pgd = pgdp + pgd_index(addr);
+ if (!pgd_present(*pgd)) {
+ addr = pgd_addr_end(addr, end);
+ continue;
+ }
+
+ /* On ARMv7 xxx_addr_end() - works if memory not allocated
+ * above 4GB.
+ */
+ pgdir_end = pgd_addr_end(addr, end);
+ while (addr < pgdir_end) {
+ /* give up CPU if mmu_lock is needed by other vCPUs */
+ if (need_resched() || spin_needbreak(&kvm->mmu_lock))
+ cond_resched_lock(&kvm->mmu_lock);
+
+ pud = pud_offset(pgd, addr);
+ if (!pud_present(*pud)) {
+ addr = stage2pud_addr_end(addr, end);
+ continue;
+ }
+
+ /* Fail if PUD is huge, splitting PUDs not supported */
+ if (pud_huge(*pud)) {
+ spin_unlock(&kvm->mmu_lock);
+ return -EFAULT;
+ }
+
+ /* By default 'nopud' is supported which fails with
+ * guests larger 1GB. Technically not needed since
+ * 3-level page tables are supported, but 4-level may
+ * be used in the future, on 64 bit pud_addr_end() will
+ * work.
+ */
+ pud_end = stage2pud_addr_end(addr, end);
+ while (addr < pud_end) {
+ if (need_resched() ||
+ spin_needbreak(&kvm->mmu_lock))
+ cond_resched_lock(&kvm->mmu_lock);
+
+ pmd = pmd_offset(pud, addr);
+ if (!pmd_present(*pmd)) {
+ addr = pmd_addr_end(addr, end);
+ continue;
+ }
+
+ if (kvm_pmd_huge(*pmd)) {
+ ret = split_pmd(kvm, pmd, addr);
+ if (ret < 0) {
+ /* Failed to split up huge
+ * page abort.
+ */
+ spin_unlock(&kvm->mmu_lock);
+ return ret;
+ }
+ addr = pmd_addr_end(addr, end);
+ continue;
+ }
+
+ pmd_end = pmd_addr_end(addr, end);
+ while (addr < pmd_end) {
+ pte = pte_offset_kernel(pmd, addr);
+ addr += PAGE_SIZE;
+ if (!pte_present(*pte))
+ continue;
+ /* skip write protected pages */
+ if ((*pte & L_PTE_S2_RDWR) ==
+ L_PTE_S2_RDONLY)
+ continue;
+ stage2_mark_pte_ro(pte);
+ }
+ }
+ }
+ }
+ /* Flush TLBs, >= ARMv7 variant uses hardware broadcast not IPIs */
+ kvm_flush_remote_tlbs(kvm);
+ spin_unlock(&kvm->mmu_lock);
+ return 0;
+}
+
static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
struct kvm_memory_slot *memslot,
unsigned long fault_status)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 03a0381..1d11912 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -184,7 +184,10 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
return called;
}

-void kvm_flush_remote_tlbs(struct kvm *kvm)
+/* Architectures like >= ARMv7 hardware broadcast TLB invalidations and don't
+ * use IPIs.
+ */
+void __weak kvm_flush_remote_tlbs(struct kvm *kvm)
{
long dirty_count = kvm->tlbs_dirty;

--
1.7.9.5