Re: [PATCH v9 4/4] arm: ARMv7 dirty page logging 2nd stage page fault handling support

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

On 08/11/2014 12:13 PM, Christoffer Dall wrote:
> On Thu, Jul 24, 2014 at 05:56:08PM -0700, 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 will be used again.
>>
>> Signed-off-by: Mario Smarduch <m.smarduch@samsung.com>
>> ---
>>  arch/arm/kvm/mmu.c |   31 +++++++++++++++++++++++++------
>>  1 file changed, 25 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index ca84331..a17812a 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -642,7 +642,8 @@ 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)
>>  {
>>  	pmd_t *pmd;
>>  	pte_t *pte, old_pte;
>> @@ -657,6 +658,15 @@ 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;
>> +		clear_pmd_entry(kvm, pmd, ipa);
> 
> clear_pmd_entry has a VM_BUG_ON(kvm_pmd_huge(*pmd)) so that is
> definitely not the right thing to call.

I don't see that in 3.15rc1/rc4 -

static void clear_pmd_entry(struct kvm *kvm, pmd_t *pmd, phys_addr_t addr)
{
        if (kvm_pmd_huge(*pmd)) {
                pmd_clear(pmd);
                kvm_tlb_flush_vmid_ipa(kvm, addr);
        } else {
                  [....]
}

I thought the purpose of this function was to clear PMD entry. Also
ran hundreds of tests no problems. Hmmm confused.

> 
>> +	}
>> +
>>  	/* Create stage-2 page mappings - Level 2 */
>>  	if (pmd_none(*pmd)) {
>>  		if (!cache)
>> @@ -709,7 +719,7 @@ 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;
>> @@ -926,6 +936,12 @@ 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;
>> +	/* Get logging status, if dirty_bitmap is not NULL then logging is on */
>> +	#ifdef CONFIG_ARM
>> +		bool logging_active = !!memslot->dirty_bitmap;
>> +	#else
>> +		bool logging_active = false;
>> +	#endif
> 
> can you make this an inline in the header files for now please?

Yes definitely.

> 
>>  
>>  	write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
>>  	if (fault_status == FSC_PERM && !write_fault) {
>> @@ -936,7 +952,7 @@ 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 {
>> @@ -979,7 +995,7 @@ 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) {
>> @@ -998,9 +1014,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>  			kvm_set_pfn_dirty(pfn);
>>  		}
>>  		coherent_cache_guest_page(vcpu, hva, PAGE_SIZE);
>> -		ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, false);
>> +		ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, false,
>> +					logging_active);
>>  	}
>>  
>> +	if (write_fault)
>> +		mark_page_dirty(kvm, gfn);
>>  
>>  out_unlock:
>>  	spin_unlock(&kvm->mmu_lock);
>> @@ -1151,7 +1170,7 @@ 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);
>> +	stage2_set_pte(kvm, NULL, gpa, pte, false, false);
> 
> why is logging never active if we are called from MMU notifiers?

mmu notifiers update sptes, but I don't see how these updates
can result in guest dirty pages. Also guest pages are marked dirty
from 2nd stage page fault handlers (searching through the code).

> 
>>  }
>>  
>>  
>> -- 
>> 1.7.9.5
>>
> 
> Thanks,
> -Christoffer
>