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

[Mario Smarduch <m.smarduch@samsung.com>]

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.
>