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Date: Mon, 3 Dec 2018 17:41:55 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Punit Agrawal <punit.agrawal@....com>, kvmarm@...ts.cs.columbia.edu
Cc: suzuki.poulose@....com, 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()
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.
>
> 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.
> +
> /*
> * 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.
> + 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 .
> + }
> +
> + 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.
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