Re: [PATCH v13 7/7] arm: KVM: ARMv7 dirty page logging 2nd stage page fault

Marc Zyngier
2014-11-07T10:33:20Z

On 07/11/14 00:40, Mario Smarduch wrote:
> This patch adds support for handling 2nd stage page faults during migration,
> it disables faulting in huge pages, and dissolves huge pages to page tables.
> In case migration is canceled huge pages are used again.
>
> Reviewed-by: Christoffer Dall <christoffer.dall at linaro.org>
> Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
> ---
> arch/arm/kvm/mmu.c | 47 ++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 40 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 2f5131e..d511fc0 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -47,6 +47,15 @@ static phys_addr_t hyp_idmap_vector;
> #define kvm_pmd_huge(_x) (pmd_huge(_x) || pmd_trans_huge(_x))
> #define kvm_pud_huge(_x) pud_huge(_x)
>
> +static bool kvm_get_logging_state(struct kvm_memory_slot *memslot)
> +{
> +#ifdef CONFIG_ARM
> + return !!memslot->dirty_bitmap;
> +#else
> + return false;
> +#endif
> +}
> +
> static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> {
> /*
> @@ -626,7 +635,8 @@ static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
> }
>
> static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> - phys_addr_t addr, const pte_t *new_pte, bool iomap)
> + phys_addr_t addr, const pte_t *new_pte, bool iomap,
> + bool logging_active)

Yuk. Yet another parameter. Can't we have a set of flags instead,
indicating both iomap and logging in one go? That would make things more
readable (at least for me).

> {
> pmd_t *pmd;
> pte_t *pte, old_pte;
> @@ -641,6 +651,18 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> return 0;
> }
>
> + /*
> + * While dirty memory logging, clear PMD entry for huge page and split
> + * into smaller pages, to track dirty memory at page granularity.
> + */
> + if (logging_active && kvm_pmd_huge(*pmd)) {
> + phys_addr_t ipa = pmd_pfn(*pmd) << PAGE_SHIFT;
> +
> + pmd_clear(pmd);
> + kvm_tlb_flush_vmid_ipa(kvm, ipa);
> + put_page(virt_to_page(pmd));
> + }
> +

If we have huge PUDs (like on arn64 with 4k Pages and 4 levels of
translation), would we need something similar? If that's the case, a
comment would be very welcome.

> /* Create stage-2 page mappings - Level 2 */
> if (pmd_none(*pmd)) {
> if (!cache)
> @@ -693,7 +715,7 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
> if (ret)
> goto out;
> spin_lock(&kvm->mmu_lock);
> - ret = stage2_set_pte(kvm, &cache, addr, &pte, true);
> + ret = stage2_set_pte(kvm, &cache, addr, &pte, true, false);
> spin_unlock(&kvm->mmu_lock);
> if (ret)
> goto out;
> @@ -910,6 +932,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct vm_area_struct *vma;
> pfn_t pfn;
> pgprot_t mem_type = PAGE_S2;
> + bool logging_active = kvm_get_logging_state(memslot);
>
> write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
> if (fault_status == FSC_PERM && !write_fault) {
> @@ -920,7 +943,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> /* Let's check if we will get back a huge page backed by hugetlbfs */
> down_read(&current->mm->mmap_sem);
> vma = find_vma_intersection(current->mm, hva, hva + 1);
> - if (is_vm_hugetlb_page(vma)) {
> + if (is_vm_hugetlb_page(vma) && !logging_active) {
> hugetlb = true;
> gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
> } else {
> @@ -966,7 +989,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> spin_lock(&kvm->mmu_lock);
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
> - if (!hugetlb && !force_pte)
> + if (!hugetlb && !force_pte && !logging_active)
> hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
>
> if (hugetlb) {
> @@ -986,10 +1009,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> }
> coherent_cache_guest_page(vcpu, hva, PAGE_SIZE);
> ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte,
> - mem_type == PAGE_S2_DEVICE);
> + mem_type == PAGE_S2_DEVICE,
> + logging_active);
> }
>
> -
> + if (write_fault)
> + mark_page_dirty(kvm, gfn);
> out_unlock:
> spin_unlock(&kvm->mmu_lock);
> kvm_release_pfn_clean(pfn);
> @@ -1139,7 +1164,15 @@ static void kvm_set_spte_handler(struct kvm *kvm, gpa_t gpa, void *data)
> {
> pte_t *pte = (pte_t *)data;
>
> - stage2_set_pte(kvm, NULL, gpa, pte, false);
> + /*
> + * We can always call stage2_set_pte with logging_active == false,
> + * because MMU notifiers will have unmapped a huge PMD before calling
> + * ->change_pte() (which in turn calls kvm_set_spte_hva()) and therefore
> + * stage2_set_pte() never needs to clear out a huge PMD through this
> + * calling path.
> + */
> +
> + stage2_set_pte(kvm, NULL, gpa, pte, false, false);
> }
>
>
>

Thanks,

M.
--
Jazz is not dead. It just smells funny...