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Date: Mon, 3 Dec 2018 13:37:37 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Anshuman Khandual <anshuman.khandual@....com>,
kvmarm@...ts.cs.columbia.edu
Cc: marc.zyngier@....com, will.deacon@....com,
linux-kernel@...r.kernel.org,
Christoffer Dall <christoffer.dall@....com>,
punitagrawal@...il.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 1/8] KVM: arm/arm64: Share common code in
user_mem_abort()
Hi Anshuman,
On 03/12/2018 12:11, Anshuman Khandual wrote:
>
>
> On 10/31/2018 11:27 PM, Punit Agrawal wrote:
>> The code for operations such as marking the pfn as dirty, and
>> dcache/icache maintenance during stage 2 fault handling is duplicated
>> between normal pages and PMD hugepages.
>>
>> Instead of creating another copy of the operations when we introduce
>> PUD hugepages, let's share them across the different pagesizes.
>>
>> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
>> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Cc: Christoffer Dall <christoffer.dall@....com>
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> ---
>> virt/kvm/arm/mmu.c | 49 ++++++++++++++++++++++++++++------------------
>> 1 file changed, 30 insertions(+), 19 deletions(-)
>>
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index 5eca48bdb1a6..59595207c5e1 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>> @@ -1475,7 +1475,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> unsigned long fault_status)
>> {
>> int ret;
>> - bool write_fault, exec_fault, writable, hugetlb = false, force_pte = false;
>> + bool write_fault, exec_fault, writable, force_pte = false;
>> unsigned long mmu_seq;
>> gfn_t gfn = fault_ipa >> PAGE_SHIFT;
>> struct kvm *kvm = vcpu->kvm;
>> @@ -1484,7 +1484,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> kvm_pfn_t pfn;
>> pgprot_t mem_type = PAGE_S2;
>> bool logging_active = memslot_is_logging(memslot);
>> - unsigned long flags = 0;
>> + unsigned long vma_pagesize, flags = 0;
>
> A small nit s/vma_pagesize/pagesize. Why call it VMA ? Its implicit.
May be we could call it mapsize. pagesize is confusing.
>
>>
>> write_fault = kvm_is_write_fault(vcpu);
>> exec_fault = kvm_vcpu_trap_is_iabt(vcpu);
>> @@ -1504,10 +1504,16 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> return -EFAULT;
>> }
>>
>> - if (vma_kernel_pagesize(vma) == PMD_SIZE && !logging_active) {
>> - hugetlb = true;
>> + vma_pagesize = vma_kernel_pagesize(vma);
>> + if (vma_pagesize == PMD_SIZE && !logging_active) {
>> gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
>> } else {
>> + /*
>> + * Fallback to PTE if it's not one of the Stage 2
>> + * supported hugepage sizes
>> + */
>> + vma_pagesize = PAGE_SIZE;
>
> This seems redundant and should be dropped. vma_kernel_pagesize() here either
> calls hugetlb_vm_op_pagesize (via hugetlb_vm_ops->pagesize) or simply returns
> PAGE_SIZE. The vm_ops path is taken if the QEMU VMA covering any given HVA is
> backed either by HugeTLB pages or simply normal pages. vma_pagesize would
> either has a value of PMD_SIZE (HugeTLB hstate based) or PAGE_SIZE. Hence if
> its not PMD_SIZE it must be PAGE_SIZE which should not be assigned again.
We may want to force using the PTE mappings when logging_active (e.g, migration
?) to prevent keep tracking of huge pages. So the check is still valid.
>
>> +
>> /*
>> * Pages belonging to memslots that don't have the same
>> * alignment for userspace and IPA cannot be mapped using
>> @@ -1573,23 +1579,33 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> if (mmu_notifier_retry(kvm, mmu_seq))
>> goto out_unlock;
>>
>> - if (!hugetlb && !force_pte)
>> - hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
>> + if (vma_pagesize == PAGE_SIZE && !force_pte) {
>> + /*
>> + * Only PMD_SIZE transparent hugepages(THP) are
>> + * currently supported. This code will need to be
>> + * updated to support other THP sizes.
>> + */
>
> This comment belongs to transparent_hugepage_adjust() but not here.
I think this is relevant here than in thp_adjust, unless we rename
the function below to something generic, handle_hugepage_adjust().
>> + if (transparent_hugepage_adjust(&pfn, &fault_ipa))
>> + vma_pagesize = PMD_SIZE;
>
> IIUC transparent_hugepage_adjust() is only getting called here. Instead of
> returning 'true' when it is able to detect a huge page backing and doing
> an adjustment there after, it should rather return THP size (PMD_SIZE) to
> accommodate probable multi size THP support in future .
That makes sense.
>
>> + }
>> +
>> + if (writable)
>> + kvm_set_pfn_dirty(pfn);
>>
>> - if (hugetlb) {
>> + if (fault_status != FSC_PERM)
>> + clean_dcache_guest_page(pfn, vma_pagesize);
>> +
>> + if (exec_fault)
>> + invalidate_icache_guest_page(pfn, vma_pagesize);
>> +
>> + if (vma_pagesize == PMD_SIZE) {
>> pmd_t new_pmd = pfn_pmd(pfn, mem_type);
>> new_pmd = pmd_mkhuge(new_pmd);
>> - if (writable) {
>> + if (writable)
>> new_pmd = kvm_s2pmd_mkwrite(new_pmd);
>> - kvm_set_pfn_dirty(pfn);
>> - }
>> -
>> - if (fault_status != FSC_PERM)
>> - clean_dcache_guest_page(pfn, PMD_SIZE);
>>
>> if (exec_fault) {
>> new_pmd = kvm_s2pmd_mkexec(new_pmd);
>> - invalidate_icache_guest_page(pfn, PMD_SIZE);
>> } else if (fault_status == FSC_PERM) {
>> /* Preserve execute if XN was already cleared */
>> if (stage2_is_exec(kvm, fault_ipa))
>> @@ -1602,16 +1618,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>
>> if (writable) {
>> new_pte = kvm_s2pte_mkwrite(new_pte);
>> - kvm_set_pfn_dirty(pfn);
>> mark_page_dirty(kvm, gfn);
>> }
>>
>> - if (fault_status != FSC_PERM)
>> - clean_dcache_guest_page(pfn, PAGE_SIZE);
>> -
>> if (exec_fault) {
>> new_pte = kvm_s2pte_mkexec(new_pte);
>> - invalidate_icache_guest_page(pfn, PAGE_SIZE);
>> } else if (fault_status == FSC_PERM) {
>> /* Preserve execute if XN was already cleared */
>> if (stage2_is_exec(kvm, fault_ipa))
>>
>
> kvm_set_pfn_dirty, clean_dcache_guest_page, invalidate_icache_guest_page
> can all be safely moved before setting the page table entries either as
> PMD or PTE.
I think this is what we do currently. So I assume this is fine.
Cheers
Suzuki
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