Re: [PATCH v3 17/21] KVM: arm64: Convert user_mem_abort() to generic page-table API

Gavin Shan
2020-09-03T06:06:44Z

Hi Will,

On 8/25/20 7:39 PM, Will Deacon wrote:
> Convert user_mem_abort() to call kvm_pgtable_stage2_relax_perms() when
> handling a stage-2 permission fault and kvm_pgtable_stage2_map() when
> handling a stage-2 translation fault, rather than walking the page-table
> manually.
>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
> arch/arm64/kvm/mmu.c | 112 +++++++++++++------------------------------
> 1 file changed, 34 insertions(+), 78 deletions(-)
>

I looks good to me. As it's changing the stage2 page table management
mechanism completely. I will test this series with various configuration
on different machines. I will update the result when it's finished.

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index d4b0716a6ab4..cfbf32cae3a5 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1491,7 +1491,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> {
> int ret;
> bool write_fault, writable, force_pte = false;
> - bool exec_fault, needs_exec;
> + bool exec_fault;
> + bool device = false;
> unsigned long mmu_seq;
> gfn_t gfn = fault_ipa >> PAGE_SHIFT;
> struct kvm *kvm = vcpu->kvm;
> @@ -1499,10 +1500,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct vm_area_struct *vma;
> short vma_shift;
> kvm_pfn_t pfn;
> - pgprot_t mem_type = PAGE_S2;
> bool logging_active = memslot_is_logging(memslot);
> - unsigned long vma_pagesize, flags = 0;
> - struct kvm_s2_mmu *mmu = vcpu->arch.hw_mmu;
> + unsigned long vma_pagesize;
> + enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
> + struct kvm_pgtable *pgt;
>
> write_fault = kvm_is_write_fault(vcpu);
> exec_fault = kvm_vcpu_trap_is_iabt(vcpu);
> @@ -1535,22 +1536,16 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> vma_pagesize = PAGE_SIZE;
> }
>
> - /*
> - * The stage2 has a minimum of 2 level table (For arm64 see
> - * kvm_arm_setup_stage2()). Hence, we are guaranteed that we can
> - * use PMD_SIZE huge mappings (even when the PMD is folded into PGD).
> - * As for PUD huge maps, we must make sure that we have at least
> - * 3 levels, i.e, PMD is not folded.
> - */
> - if (vma_pagesize == PMD_SIZE ||
> - (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm)))
> + if (vma_pagesize == PMD_SIZE || vma_pagesize == PUD_SIZE)
> gfn = (fault_ipa & huge_page_mask(hstate_vma(vma))) >> PAGE_SHIFT;
> mmap_read_unlock(current->mm);
>
> - /* We need minimum second+third level pages */
> - ret = kvm_mmu_topup_memory_cache(memcache, kvm_mmu_cache_min_pages(kvm));
> - if (ret)
> - return ret;
> + if (fault_status != FSC_PERM) {
> + ret = kvm_mmu_topup_memory_cache(memcache,
> + kvm_mmu_cache_min_pages(kvm));
> + if (ret)
> + return ret;
> + }
>
> mmu_seq = vcpu->kvm->mmu_notifier_seq;
> /*
> @@ -1573,28 +1568,20 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
>
> if (kvm_is_device_pfn(pfn)) {
> - mem_type = PAGE_S2_DEVICE;
> - flags |= KVM_S2PTE_FLAG_IS_IOMAP;
> - } else if (logging_active) {
> - /*
> - * Faults on pages in a memslot with logging enabled
> - * should not be mapped with huge pages (it introduces churn
> - * and performance degradation), so force a pte mapping.
> - */
> - flags |= KVM_S2_FLAG_LOGGING_ACTIVE;
> -
> + device = true;
> + } else if (logging_active && !write_fault) {
> /*
> * Only actually map the page as writable if this was a write
> * fault.
> */
> - if (!write_fault)
> - writable = false;
> + writable = false;
> }
>
> - if (exec_fault && is_iomap(flags))
> + if (exec_fault && device)
> return -ENOEXEC;
>
> spin_lock(&kvm->mmu_lock);
> + pgt = vcpu->arch.hw_mmu->pgt;
> if (mmu_notifier_retry(kvm, mmu_seq))
> goto out_unlock;
>
> @@ -1605,62 +1592,31 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (vma_pagesize == PAGE_SIZE && !force_pte)
> vma_pagesize = transparent_hugepage_adjust(memslot, hva,
> &pfn, &fault_ipa);
> - if (writable)
> + if (writable) {
> + prot |= KVM_PGTABLE_PROT_W;
> kvm_set_pfn_dirty(pfn);
> + mark_page_dirty(kvm, gfn);
> + }
>
> - if (fault_status != FSC_PERM && !is_iomap(flags))
> + if (fault_status != FSC_PERM && !device)
> clean_dcache_guest_page(pfn, vma_pagesize);
>
> - if (exec_fault)
> + if (exec_fault) {
> + prot |= KVM_PGTABLE_PROT_X;
> invalidate_icache_guest_page(pfn, vma_pagesize);
> + }
>
> - /*
> - * If we took an execution fault we have made the
> - * icache/dcache coherent above and should now let the s2
> - * mapping be executable.
> - *
> - * Write faults (!exec_fault && FSC_PERM) are orthogonal to
> - * execute permissions, and we preserve whatever we have.
> - */
> - needs_exec = exec_fault ||
> - (fault_status == FSC_PERM &&
> - stage2_is_exec(mmu, fault_ipa, vma_pagesize));
> -
> - if (vma_pagesize == PUD_SIZE) {
> - pud_t new_pud = kvm_pfn_pud(pfn, mem_type);
> -
> - new_pud = kvm_pud_mkhuge(new_pud);
> - if (writable)
> - new_pud = kvm_s2pud_mkwrite(new_pud);
> -
> - if (needs_exec)
> - new_pud = kvm_s2pud_mkexec(new_pud);
> -
> - ret = stage2_set_pud_huge(mmu, memcache, fault_ipa, &new_pud);
> - } else if (vma_pagesize == PMD_SIZE) {
> - pmd_t new_pmd = kvm_pfn_pmd(pfn, mem_type);
> -
> - new_pmd = kvm_pmd_mkhuge(new_pmd);
> -
> - if (writable)
> - new_pmd = kvm_s2pmd_mkwrite(new_pmd);
> -
> - if (needs_exec)
> - new_pmd = kvm_s2pmd_mkexec(new_pmd);
> + if (device)
> + prot |= KVM_PGTABLE_PROT_DEVICE;
> + else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC))
> + prot |= KVM_PGTABLE_PROT_X;
>
> - ret = stage2_set_pmd_huge(mmu, memcache, fault_ipa, &new_pmd);
> + if (fault_status == FSC_PERM) {
> + ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
> } else {
> - pte_t new_pte = kvm_pfn_pte(pfn, mem_type);
> -
> - if (writable) {
> - new_pte = kvm_s2pte_mkwrite(new_pte);
> - mark_page_dirty(kvm, gfn);
> - }
> -
> - if (needs_exec)
> - new_pte = kvm_s2pte_mkexec(new_pte);
> -
> - ret = stage2_set_pte(mmu, memcache, fault_ipa, &new_pte, flags);
> + ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
> + __pfn_to_phys(pfn), prot,
> + memcache);
> }
>
> out_unlock:
>

Thanks,
Gavin