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

Mario Smarduch
2014-11-07T19:21:54Z

On 11/07/2014 02:33 AM, Marc Zyngier wrote:
> 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).

Sure that could be changed, I didn't like the idea adding another line
myself, needed some suggestions.

>
>> {
>> 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.

I'm not sure what we do if we encounter a huge pud, break that
up into small pages? I was thinking if huge puds are enabled
then disable page logging. I don't know what kind of comment to
put in here now other then it's not supported

>
>> /* 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.
>