RE: [PATCH v2 06/14] KVM: ARM: Memory virtualization setup

Min-gyu Kim
2012-10-05T02:23:34Z

> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On
> Behalf Of Christoffer Dall
> Sent: Monday, October 01, 2012 6:11 PM
> To: kvm@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> kvmarm@lists.cs.columbia.edu
> Cc: Marc Zyngier
> Subject: [PATCH v2 06/14] KVM: ARM: Memory virtualization setup
>
> +static void stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache
> *cache,
> + phys_addr_t addr, const pte_t *new_pte) {
> + pgd_t *pgd;
> + pud_t *pud;
> + pmd_t *pmd;
> + pte_t *pte, old_pte;
> +
> + /* Create 2nd stage page table mapping - Level 1 */
> + pgd = kvm->arch.pgd + pgd_index(addr);
> + pud = pud_offset(pgd, addr);
> + if (pud_none(*pud)) {
> + if (!cache)
> + return; /* ignore calls from kvm_set_spte_hva */
> + pmd = mmu_memory_cache_alloc(cache);
> + pud_populate(NULL, pud, pmd);
> + pmd += pmd_index(addr);
> + get_page(virt_to_page(pud));
> + } else
> + pmd = pmd_offset(pud, addr);
> +
> + /* Create 2nd stage page table mapping - Level 2 */
> + if (pmd_none(*pmd)) {
> + if (!cache)
> + return; /* ignore calls from kvm_set_spte_hva */
> + pte = mmu_memory_cache_alloc(cache);
> + clean_pte_table(pte);
> + pmd_populate_kernel(NULL, pmd, pte);
> + pte += pte_index(addr);
> + get_page(virt_to_page(pmd));
> + } else
> + pte = pte_offset_kernel(pmd, addr);
> +
> + /* Create 2nd stage page table mapping - Level 3 */
> + old_pte = *pte;
> + set_pte_ext(pte, *new_pte, 0);
> + if (pte_present(old_pte))
> + __kvm_tlb_flush_vmid(kvm);
> + else
> + get_page(virt_to_page(pte));
> +}

I'm not sure about the 3-level page table, but isn't it necessary to
clean the page table for 2nd level?
There are two mmu_memory_cache_alloc calls. One has following clean_pte_table
and the other doesn't have.

And why do you ignore calls from kvm_set_spte_hva? It is supposed to happen when
host moves the page, right? Then you ignore the case because it can be handled
later when fault actually happens? Is there any other reason that I miss?