[PATCH v6 2/4] live migration support for initial write protect of VM
Mario Smarduch
m.smarduch at samsung.com
Thu May 15 11:27:29 PDT 2014
Patch adds memslot support for initial write protection and split up of huge
pages
Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
---
arch/arm/include/asm/kvm_host.h | 8 +++
arch/arm/include/asm/kvm_mmu.h | 10 +++
arch/arm/kvm/arm.c | 3 +
arch/arm/kvm/mmu.c | 143 +++++++++++++++++++++++++++++++++++++++
4 files changed, 164 insertions(+)
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 193ceaf..0e55b17 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
@@ -231,4 +237,6 @@ int kvm_perf_teardown(void);
u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid);
int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);
+int kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
+
#endif /* __ARM_KVM_HOST_H__ */
diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index 5c7aa3c..7f9d9d3 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -114,6 +114,16 @@ static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
pmd_val(*pmd) |= L_PMD_S2_RDWR;
}
+static inline void kvm_set_s2pte_readonly(pte_t *pte)
+{
+ pte_val(*pte) &= ~(L_PTE_S2_RDONLY ^ L_PTE_S2_RDWR);
+}
+
+static inline bool kvm_s2pte_readonly(pte_t *pte)
+{
+ return (pte_val(*pte) & L_PTE_S2_RDWR) == L_PTE_S2_RDONLY;
+}
+
/* Open coded p*d_addr_end that can deal with 64bit addresses */
#define kvm_pgd_addr_end(addr, end) \
({ u64 __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK; \
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 3c82b37..1055266 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -234,6 +234,9 @@ 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 eea3f0a..b71ad27 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -748,6 +748,149 @@ static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
return false;
}
+
+/*
+ * Walks PMD page table range and write protects it. Called with
+ * 'kvm->mmu_lock' * held
+ */
+static void stage2_wp_pmd_range(phys_addr_t addr, phys_addr_t end, pmd_t *pmd)
+{
+ pte_t *pte;
+
+ while (addr < end) {
+ pte = pte_offset_kernel(pmd, addr);
+ addr += PAGE_SIZE;
+ if (!pte_present(*pte))
+ continue;
+ /* skip write protected pages */
+ if (kvm_s2pte_readonly(pte))
+ continue;
+ kvm_set_s2pte_readonly(pte);
+ }
+}
+
+/*
+ * Walks PUD page table range to write protects it , if necessary spluts up
+ * huge pages to small pages. Called with 'kvm->mmu_lock' held.
+ */
+static void stage2_wp_pud_range(struct kvm *kvm, phys_addr_t addr,
+ phys_addr_t end, pud_t *pud)
+{
+ pmd_t *pmd;
+ phys_addr_t pmd_end;
+
+ while (addr < end) {
+ /* If needed give up CPU during PUD page table walk */
+ if (need_resched() || spin_needbreak(&kvm->mmu_lock))
+ cond_resched_lock(&kvm->mmu_lock);
+
+ pmd = pmd_offset(pud, addr);
+ if (!pmd_present(*pmd)) {
+ addr = kvm_pmd_addr_end(addr, end);
+ continue;
+ }
+
+ if (kvm_pmd_huge(*pmd)) {
+ /*
+ * Clear pmd entry DABT handler will install smaller
+ * pages.
+ */
+ clear_pmd_entry(kvm, pmd, addr);
+ addr = kvm_pmd_addr_end(addr, end);
+ continue;
+ }
+
+ pmd_end = kvm_pmd_addr_end(addr, end);
+ stage2_wp_pmd_range(addr, pmd_end, pmd);
+ addr = pmd_end;
+ }
+}
+
+/*
+ * Walks PGD page table range to write protect it. Called with 'kvm->mmu_lock'
+ * held.
+ */
+static int stage2_wp_pgd_range(struct kvm *kvm, phys_addr_t addr,
+ phys_addr_t end, pgd_t *pgd)
+{
+ phys_addr_t pud_end;
+ pud_t *pud;
+
+ while (addr < 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 = kvm_pud_addr_end(addr, end);
+ continue;
+ }
+
+ /* Fail if PUD is huge, splitting PUDs not supported */
+ if (pud_huge(*pud))
+ return -EFAULT;
+
+ /*
+ * By default 'nopud' folds third level page tables.
+ * Implement for future support of 4-level tables
+ */
+ pud_end = kvm_pud_addr_end(addr, end);
+ stage2_wp_pud_range(kvm, addr, pud_end, pud);
+ addr = pud_end;
+ }
+ return 0;
+}
+
+/**
+ * kvm_mmu_slot_remove_access() - write protects entire memslot address space.
+ *
+ * Called at start of live migration when KVM_MEM_LOG_DIRTY_PAGES ioctl is
+ * issued. After this function returns all pages (minus the ones faulted
+ * in or released when mmu_lock is given up) must be write protected to
+ * keep track of dirty pages to migrate on subsequent dirty log read.
+ * 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;
+ pgd_t *pgdp = kvm->arch.pgd;
+ struct kvm_memory_slot *memslot = id_to_memslot(kvm->memslots, slot);
+ phys_addr_t addr = memslot->base_gfn << PAGE_SHIFT;
+ phys_addr_t end = (memslot->base_gfn + memslot->npages) << PAGE_SHIFT;
+ phys_addr_t pgdir_end;
+ int ret = -ENOMEM;
+
+ 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 = kvm_pgd_addr_end(addr, end);
+ continue;
+ }
+
+ pgdir_end = kvm_pgd_addr_end(addr, end);
+ ret = stage2_wp_pgd_range(kvm, addr, pgdir_end, pgd);
+ /* Failed to WP a pgd range abort */
+ if (ret < 0)
+ goto out;
+ addr = pgdir_end;
+ }
+ ret = 0;
+ /* Flush TLBs, >= ARMv7 variant uses hardware broadcast not IPIs */
+ kvm_flush_remote_tlbs(kvm);
+out:
+ spin_unlock(&kvm->mmu_lock);
+ return ret;
+}
+
static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
struct kvm_memory_slot *memslot,
unsigned long fault_status)
--
1.7.9.5
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