On Thu, Apr 17 2014 at 2:34:39 am BST, Mario Smarduch <m.smarduch@xxxxxxxxxxx> wrote:
> Additional logic to handle second stage page faults during migration. Primarily
> page faults are prevented from creating huge pages.
>
>
> Signed-off-by: Mario Smarduch <m.smarduch@xxxxxxxxxxx>
> ---
> arch/arm/kvm/mmu.c | 33 +++++++++++++++++++++++++++++++--
> 1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 47bec1c..ebec33c 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -839,6 +839,7 @@ 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) {
> @@ -890,12 +891,22 @@ 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 initially, prevent pmd update if it's split up.
> + */
> + migration_active = vcpu->kvm->arch.migration_in_progress;
> +
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
> - if (!hugetlb && !force_pte)
> +
> + /* During migration don't rebuild huge pages */
> + if (!hugetlb && !force_pte && !migration_active)
> hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
>
> - if (hugetlb) {
> + /* Steer away from installing PMDs if migrating, migration failed,
> + * or this an initial page fault. Migrating huge pages is too slow.
> + */
> + if (!migration_active && hugetlb) {
> pmd_t new_pmd = pfn_pmd(pfn, PAGE_S2);
> new_pmd = pmd_mkhuge(new_pmd);
> if (writable) {
> @@ -907,6 +918,22 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> } else {
> pte_t new_pte = pfn_pte(pfn, PAGE_S2);
> if (writable) {
> + /* First convert huge page pfn to normal 4k page pfn,
> + * while migration is in progress.
> + * Second in migration mode and rare case where
> + * splitting of huge pages fails check if pmd is
> + * mapping a huge page if it is then clear it so
> + * stage2_set_pte() can map in a small page.
> + */
> + if (migration_active && hugetlb) {
> + pmd_t *pmd;
> + pfn += (fault_ipa >> PAGE_SHIFT) &
> + (PTRS_PER_PMD-1);
Shouldn't that be "pfn += pte_index(fault_addr);"?
> + 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);
> + }
> kvm_set_s2pte_writable(&new_pte);
> kvm_set_pfn_dirty(pfn);
> }
> @@ -914,6 +941,8 @@ 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);
> }
>
> + if (writable)
Shouldn't that be done only when migration is active?
> + mark_page_dirty(kvm, gfn);
>
> out_unlock:
> spin_unlock(&kvm->mmu_lock);
--
Jazz is not dead. It just smells funny.
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