Subject: [PATCH v2 1/2] KVM: ARM: Support hugetlbfs backed huge pages

From: [email-masked] (Marc Zyngier)
Date: Fri, 04 Oct 2013 09:50:35 +0100

Hi Christoffer,

On 03/10/13 21:36, Christoffer Dall wrote:
> Support huge pages in KVM/ARM and KVM/ARM64.  The pud_huge checking on
> the unmap path may feel a bit silly as the pud_huge check is always
> defined to false, but the compiler should be smart about this.
> 
> Note: This deals only with VMAs marked as huge which are allocated by
> users through hugetlbfs only.  Transparent huge pages can only be
> detected by looking at the underlying pages (or the page tables
> themselves) and this patch so far simply maps these on a page-by-page
> level in the Stage-2 page tables.
> 
> Signed-off-by: Christoffer Dall <[email-masked]>
> 
> ---
> Changelog[v2]:
>  - Invaliate TLB on clearing stage-2 huge page entries
>  - Restructure unmap_range to share more code
>  - Share stage_2 pmd allocation
>  - Factor out THP support to separate patch
>  - Fix incorrect gfn_to_pfn_prot and mmu_seq ordering
> ---
>  arch/arm/include/asm/kvm_mmu.h   |   17 +++-
>  arch/arm/kvm/mmu.c               |  172 +++++++++++++++++++++++++++++---------
>  arch/arm64/include/asm/kvm_mmu.h |   12 ++-
>  3 files changed, 157 insertions(+), 44 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 9b28c41..d629fb3 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -62,6 +62,12 @@ phys_addr_t kvm_get_idmap_vector(void);
>  int kvm_mmu_init(void);
>  void kvm_clear_hyp_idmap(void);
> 
> +static inline void kvm_set_pmd(pmd_t *pmd, pmd_t new_pmd)
> +{
> +       *pmd = new_pmd;
> +       flush_pmd_entry(pmd);
> +}
> +
>  static inline void kvm_set_pte(pte_t *pte, pte_t new_pte)
>  {
>         *pte = new_pte;
> @@ -103,9 +109,15 @@ static inline void kvm_set_s2pte_writable(pte_t *pte)
>         pte_val(*pte) |= L_PTE_S2_RDWR;
>  }
> 
> +static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
> +{
> +       pmd_val(*pmd) |= L_PTE_S2_RDWR;

It feels a bit weird to use a PTE specific flag to mess with a PMD. Can
you define a new flag for this?

> +}
> +
>  struct kvm;
> 
> -static inline void coherent_icache_guest_page(struct kvm *kvm, gfn_t gfn)
> +static inline void coherent_icache_guest_page(struct kvm *kvm, hva_t hva,
> +                                             unsigned long size)
>  {
>         /*
>          * If we are going to insert an instruction page and the icache is
> @@ -120,8 +132,7 @@ static inline void coherent_icache_guest_page(struct kvm *kvm, gfn_t gfn)
>          * need any kind of flushing (DDI 0406C.b - Page B3-1392).
>          */
>         if (icache_is_pipt()) {
> -               unsigned long hva = gfn_to_hva(kvm, gfn);
> -               __cpuc_coherent_user_range(hva, hva + PAGE_SIZE);
> +               __cpuc_coherent_user_range(hva, hva + size);
>         } else if (!icache_is_vivt_asid_tagged()) {
>                 /* any kind of VIPT cache */
>                 __flush_icache_all();
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index b0de86b..cab031b 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -19,6 +19,7 @@
>  #include <linux/mman.h>
>  #include <linux/kvm_host.h>
>  #include <linux/io.h>
> +#include <linux/hugetlb.h>
>  #include <trace/events/kvm.h>
>  #include <asm/pgalloc.h>
>  #include <asm/cacheflush.h>
> @@ -41,6 +42,8 @@ static unsigned long hyp_idmap_start;
>  static unsigned long hyp_idmap_end;
>  static phys_addr_t hyp_idmap_vector;
> 
> +#define kvm_pmd_huge(_x)       (pmd_huge(_x))
> +
>  static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
>  {
>         /*
> @@ -93,19 +96,29 @@ static bool page_empty(void *ptr)
> 
>  static void clear_pud_entry(struct kvm *kvm, pud_t *pud, phys_addr_t addr)
>  {
> -       pmd_t *pmd_table = pmd_offset(pud, 0);
> -       pud_clear(pud);
> -       kvm_tlb_flush_vmid_ipa(kvm, addr);
> -       pmd_free(NULL, pmd_table);
> +       if (pud_huge(*pud)) {
> +               pud_clear(pud);
> +               kvm_tlb_flush_vmid_ipa(kvm, addr);
> +       } else {
> +               pmd_t *pmd_table = pmd_offset(pud, 0);
> +               pud_clear(pud);
> +               kvm_tlb_flush_vmid_ipa(kvm, addr);
> +               pmd_free(NULL, pmd_table);
> +       }
>         put_page(virt_to_page(pud));
>  }
> 
>  static void clear_pmd_entry(struct kvm *kvm, pmd_t *pmd, phys_addr_t addr)
>  {
> -       pte_t *pte_table = pte_offset_kernel(pmd, 0);
> -       pmd_clear(pmd);
> -       kvm_tlb_flush_vmid_ipa(kvm, addr);
> -       pte_free_kernel(NULL, pte_table);
> +       if (kvm_pmd_huge(*pmd)) {
> +               pmd_clear(pmd);
> +               kvm_tlb_flush_vmid_ipa(kvm, addr);
> +       } else {
> +               pte_t *pte_table = pte_offset_kernel(pmd, 0);
> +               pmd_clear(pmd);
> +               kvm_tlb_flush_vmid_ipa(kvm, addr);
> +               pte_free_kernel(NULL, pte_table);
> +       }
>         put_page(virt_to_page(pmd));
>  }
> 
> @@ -136,18 +149,32 @@ static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
>                         continue;
>                 }
> 
> +               if (pud_huge(*pud)) {
> +                       /*
> +                        * If we are dealing with a huge pud, just clear it and
> +                        * move on.
> +                        */
> +                       clear_pud_entry(kvm, pud, addr);
> +                       addr = pud_addr_end(addr, end);
> +                       continue;
> +               }
> +
>                 pmd = pmd_offset(pud, addr);
>                 if (pmd_none(*pmd)) {
>                         addr = pmd_addr_end(addr, end);
>                         continue;
>                 }
> 
> -               pte = pte_offset_kernel(pmd, addr);
> -               clear_pte_entry(kvm, pte, addr);
> -               next = addr + PAGE_SIZE;
> +               if (!kvm_pmd_huge(*pmd)) {
> +                       pte = pte_offset_kernel(pmd, addr);
> +                       clear_pte_entry(kvm, pte, addr);
> +                       next = addr + PAGE_SIZE;
> +               }
> 
> -               /* If we emptied the pte, walk back up the ladder */
> -               if (page_empty(pte)) {
> +               /*
> +                * If the pmd entry is to be cleared, walk back up the ladder
> +                */
> +               if (kvm_pmd_huge(*pmd) || page_empty(pte)) {
>                         clear_pmd_entry(kvm, pmd, addr);
>                         next = pmd_addr_end(addr, end);
>                         if (page_empty(pmd) && !page_empty(pud)) {
> @@ -420,29 +447,71 @@ void kvm_free_stage2_pgd(struct kvm *kvm)
>         kvm->arch.pgd = NULL;
>  }
> 
> -
> -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)
> +static pmd_t *stage2_get_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> +                            phys_addr_t addr)
>  {
>         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 0; /* ignore calls from kvm_set_spte_hva */
> +                       return NULL;
>                 pmd = mmu_memory_cache_alloc(cache);
>                 pud_populate(NULL, pud, pmd);
>                 get_page(virt_to_page(pud));
>         }
> 
> -       pmd = pmd_offset(pud, addr);
> +       return pmd_offset(pud, addr);
> +}
> +
> +static int stage2_set_pmd_huge(struct kvm *kvm, struct kvm_mmu_memory_cache
> +                              *cache, phys_addr_t addr, const pmd_t *new_pmd)
> +{
> +       pmd_t *pmd, old_pmd;
> +
> +       pmd = stage2_get_pmd(kvm, cache, addr);
> +       VM_BUG_ON(!pmd);
> 
> -       /* Create 2nd stage page table mapping - Level 2 */
> +       /*
> +        * Mapping in huge pages should only happen through a fault.  If a
> +        * page is merged into a transparent huge page, the individual
> +        * subpages of that huge page should be unmapped through MMU
> +        * notifiers before we get here.
> +        *
> +        * Merging of CompoundPages is not supported; they should become
> +        * splitting first, unmapped, merged, and mapped back in on-demand.
> +        */
> +       VM_BUG_ON(pmd_present(*pmd) && pmd_pfn(*pmd) != pmd_pfn(*new_pmd));
> +
> +       old_pmd = *pmd;
> +       kvm_set_pmd(pmd, *new_pmd);
> +       if (pmd_present(old_pmd))
> +               kvm_tlb_flush_vmid_ipa(kvm, addr);
> +       else
> +               get_page(virt_to_page(pmd));
> +       return 0;
> +}
> +
> +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)
> +{
> +       pmd_t *pmd;
> +       pte_t *pte, old_pte;
> +
> +       /* Create stage-2 page table mapping - Level 1 */
> +       pmd = stage2_get_pmd(kvm, cache, addr);
> +       if (!pmd) {
> +               /*
> +                * Ignore calls from kvm_set_spte_hva for unallocated
> +                * address ranges.
> +                */
> +               return 0;
> +       }
> +
> +       /* Create stage-2 page mappings - Level 2 */
>         if (pmd_none(*pmd)) {
>                 if (!cache)
>                         return 0; /* ignore calls from kvm_set_spte_hva */
> @@ -508,15 +577,18 @@ out:
>  }
> 
>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> -                         gfn_t gfn, struct kvm_memory_slot *memslot,
> +                         struct kvm_memory_slot *memslot,
>                           unsigned long fault_status)
>  {
> -       pte_t new_pte;
> -       pfn_t pfn;
>         int ret;
> -       bool write_fault, writable;
> +       bool write_fault, writable, hugetlb = false, force_pte = false;
>         unsigned long mmu_seq;
> +       gfn_t gfn = fault_ipa >> PAGE_SHIFT;
> +       unsigned long hva = gfn_to_hva(vcpu->kvm, gfn);
> +       struct kvm *kvm = vcpu->kvm;
>         struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
> +       struct vm_area_struct *vma;
> +       pfn_t pfn;
> 
>         write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
>         if (fault_status == FSC_PERM && !write_fault) {
> @@ -524,6 +596,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>                 return -EFAULT;
>         }
> 
> +       /* 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)) {
> +               hugetlb = true;
> +               gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
> +       } else {
> +               if (vma->vm_start & ~PMD_MASK)
> +                       force_pte = true;

What is this test for exactly? I have the feeling this is actually for
THP (since nothing in this patch is actually using force_pte), but I
don't really get it. It probably deserves a comment.

> +       }
> +       up_read(&current->mm->mmap_sem);
> +
>         /* We need minimum second+third level pages */
>         ret = mmu_topup_memory_cache(memcache, 2, KVM_NR_MEM_OBJS);
>         if (ret)
> @@ -541,26 +625,38 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>          */
>         smp_rmb();
> 
> -       pfn = gfn_to_pfn_prot(vcpu->kvm, gfn, write_fault, &writable);
> +       pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
>         if (is_error_pfn(pfn))
>                 return -EFAULT;
> 
> -       new_pte = pfn_pte(pfn, PAGE_S2);
> -       coherent_icache_guest_page(vcpu->kvm, gfn);
> -
> -       spin_lock(&vcpu->kvm->mmu_lock);
> -       if (mmu_notifier_retry(vcpu->kvm, mmu_seq))
> +       spin_lock(&kvm->mmu_lock);
> +       if (mmu_notifier_retry(kvm, mmu_seq))
>                 goto out_unlock;
> -       if (writable) {
> -               kvm_set_s2pte_writable(&new_pte);
> -               kvm_set_pfn_dirty(pfn);
> +
> +       if (hugetlb) {
> +               pmd_t new_pmd = pfn_pmd(pfn, PAGE_S2);
> +               new_pmd = pmd_mkhuge(new_pmd);
> +               if (writable) {
> +                       kvm_set_s2pmd_writable(&new_pmd);
> +                       kvm_set_pfn_dirty(pfn);
> +               }
> +               coherent_icache_guest_page(kvm, hva & PMD_MASK, PMD_SIZE);
> +               ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
> +       } else {
> +               pte_t new_pte = pfn_pte(pfn, PAGE_S2);
> +               if (writable) {
> +                       kvm_set_s2pte_writable(&new_pte);
> +                       kvm_set_pfn_dirty(pfn);
> +               }
> +               coherent_icache_guest_page(kvm, hva, PAGE_SIZE);
> +               ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, false);
>         }
> -       stage2_set_pte(vcpu->kvm, memcache, fault_ipa, &new_pte, false);
> +
> 
>  out_unlock:
> -       spin_unlock(&vcpu->kvm->mmu_lock);
> +       spin_unlock(&kvm->mmu_lock);
>         kvm_release_pfn_clean(pfn);
> -       return 0;
> +       return ret;
>  }
> 
>  /**
> @@ -629,7 +725,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
> 
>         memslot = gfn_to_memslot(vcpu->kvm, gfn);
> 
> -       ret = user_mem_abort(vcpu, fault_ipa, gfn, memslot, fault_status);
> +       ret = user_mem_abort(vcpu, fault_ipa, memslot, fault_status);
>         if (ret == 0)
>                 ret = 1;
>  out_unlock:
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index efe609c..e7f3852 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -91,6 +91,7 @@ int kvm_mmu_init(void);
>  void kvm_clear_hyp_idmap(void);
> 
>  #define        kvm_set_pte(ptep, pte)          set_pte(ptep, pte)
> +#define        kvm_set_pmd(pmdp, pmd)          set_pmd(pmdp, pmd)
> 
>  static inline bool kvm_is_write_fault(unsigned long esr)
>  {
> @@ -116,13 +117,18 @@ static inline void kvm_set_s2pte_writable(pte_t *pte)
>         pte_val(*pte) |= PTE_S2_RDWR;
>  }
> 
> +static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
> +{
> +       pmd_val(*pmd) |= PTE_S2_RDWR;
> +}

Same comment as above.

>  struct kvm;
> 
> -static inline void coherent_icache_guest_page(struct kvm *kvm, gfn_t gfn)
> +static inline void coherent_icache_guest_page(struct kvm *kvm, hva_t hva,
> +                                             unsigned long size)
>  {
>         if (!icache_is_aliasing()) {            /* PIPT */
> -               unsigned long hva = gfn_to_hva(kvm, gfn);
> -               flush_icache_range(hva, hva + PAGE_SIZE);
> +               flush_icache_range(hva, hva + size);
>         } else if (!icache_is_aivivt()) {       /* non ASID-tagged VIVT */
>                 /* any kind of VIPT cache */
>                 __flush_icache_all();

It is otherwise starting to look good.

	M.
-- 
Jazz is not dead. It just smells funny...