Subject: [PATCH 3/3] KVM: ARM: Transparent huge pages and hugetlbfs support

From: [email-masked] (Christoffer Dall)
Date: Wed, 2 Oct 2013 15:36:55 -0700

On Mon, Sep 23, 2013 at 11:11:07AM +0100, Marc Zyngier wrote:
> Hi Christoffer,
> 
> Finally taking some time to review this patch. Sorry for the delay...
> 
> On 09/08/13 05:07, Christoffer Dall wrote:
> > From: Christoffer Dall <[email-masked]>
> > 
> > Support transparent huge pages in KVM/ARM 32-bit and 64-bit.  The whole
> > transparent_hugepage_adjust stuff is far from pretty, but this is how
> > it's solved on x86 so we duplicate their logic.  This should be shared
> > across architectures if possible (like many other things), but can
> > always be changed down the road.
> > 
> > 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.
> > 
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> >  arch/arm/include/asm/kvm_mmu.h   |   17 +++-
> >  arch/arm/kvm/mmu.c               |  200 ++++++++++++++++++++++++++++++++------
> >  arch/arm64/include/asm/kvm_mmu.h |   12 ++-
> >  3 files changed, 194 insertions(+), 35 deletions(-)
> > 
> > diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> > index 472ac70..ff3ff67 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_val(*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;
> > +}
> > +
> >  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 0988d9e..26ced77 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) || pmd_trans_huge(_x))
> > +
> >  static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> >  {
> >         /*
> > @@ -93,19 +96,27 @@ 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);
> > +       } else {
> > +               pmd_t *pmd_table = pmd_offset(pud, 0);
> > +               pud_clear(pud);
> > +               kvm_tlb_flush_vmid_ipa(kvm, addr);
> > +               pmd_free(NULL, pmd_table);
> > +       }
> 
> Why don't we have any TLB invalidation on the huge path?
> 

Because this code was written before we fixed the TLB invalidation race.
Good that you spotted this.

> >         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);
> > +       } 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);
> > +       }
> 
> Same here.
> 

Same here.

> >         put_page(virt_to_page(pmd));
> >  }
> > 
> > @@ -136,12 +147,37 @@ 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;
> >                 }
> > 
> > +               if (kvm_pmd_huge(*pmd)) {
> > +                       /*
> > +                        * If we are dealing with a huge pmd, just clear it and
> > +                        * walk back up the ladder.
> > +                        */
> > +                       clear_pmd_entry(kvm, pmd, addr);
> > +                       next = pmd_addr_end(addr, end);
> > +                       if (page_empty(pmd) && !page_empty(pud)) {
> > +                               clear_pud_entry(kvm, pud, addr);
> > +                               next = pud_addr_end(addr, end);
> > +                       }
> > +                       addr = next;
> > +                       continue;
> > +               }
> 
> Looks like we already have the exact same sequence a few lines below.
> Surely we can factor it out.
> 

Yeah, the thing is having a funciton here requires us to pass in a bunch
of things, an either return the next addr or pass that by reference, and
while it does save a few lines, I found the code harder to read.  This
is another option:

static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
			unsigned long long start, u64 size)
{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	unsigned long long addr = start, end = start + size;
	u64 next;

	while (addr < end) {
		pgd = pgdp + pgd_index(addr);
		pud = pud_offset(pgd, addr);
		if (pud_none(*pud)) {
			addr = pud_addr_end(addr, end);
			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;
		}

		if (!kvm_pmd_huge(*pmd)) {
			pte = pte_offset_kernel(pmd, addr);
			clear_pte_entry(kvm, pte, addr);
			next = addr + PAGE_SIZE;
		}

		/*
		 * 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)) {
				clear_pud_entry(kvm, pud, addr);
				next = pud_addr_end(addr, end);
			}
		}

		addr = next;
	}
}

> > +
> >                 pte = pte_offset_kernel(pmd, addr);
> >                 clear_pte_entry(kvm, pte, addr);
> >                 next = addr + PAGE_SIZE;
> > @@ -420,6 +456,46 @@ void kvm_free_stage2_pgd(struct kvm *kvm)
> >         kvm->arch.pgd = NULL;
> >  }
> > 
> > +/* Set a huge page pmd entry */
> 
> Is it only for huge PMDs? Or can we try to share that code with what is
> in stage2_set_pte?
> 

We can share it, much nicer actually:

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index e2c58f5..345eefc 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -456,26 +447,33 @@ void kvm_free_stage2_pgd(struct kvm *kvm)
 	kvm->arch.pgd = NULL;
 }
 
-/* Set a huge page pmd entry */
-static int stage2_set_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
-			  phys_addr_t addr, const pmd_t *new_pmd)
+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, old_pmd;
+	pmd_t *pmd;
 
-	/* Create stage-2 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);
 
 	/*
 	 * Mapping in huge pages should only happen through a fault.  If a
@@ -500,25 +498,20 @@ static int stage2_set_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
 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)
 {
-	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 */
-		pmd = mmu_memory_cache_alloc(cache);
-		pud_populate(NULL, pud, pmd);
-		get_page(virt_to_page(pud));
+	/* 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;
 	}
 
-	pmd = pmd_offset(pud, addr);
-
-	/* Create 2nd stage page mappings - Level 2 */
+	/* Create stage-2 page mappings - Level 2 */
 	if (pmd_none(*pmd)) {
 		if (!cache)
 			return 0; /* ignore calls from kvm_set_spte_hva */
@@ -688,7 +681,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 			kvm_set_s2pmd_writable(&new_pmd);
 			kvm_set_pfn_dirty(pfn);
 		}
-		ret = stage2_set_pmd(kvm, memcache, fault_ipa, &new_pmd);
+		ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
 	} else {
 		pte_t new_pte = pfn_pte(pfn, PAGE_S2);
 		if (writable) {

> > +static int stage2_set_pmd(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> > +                         phys_addr_t addr, const pmd_t *new_pmd)
> > +{
> > +       pgd_t *pgd;
> > +       pud_t *pud;
> > +       pmd_t *pmd, old_pmd;
> > +
> > +       /* Create stage-2 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 */
> 
> Do we still need this?
> 

We didn't need it the way the code was structured in the initial
verison, but we do with sharing the code with stage2_set_pte (see
above).

> > +               pmd = mmu_memory_cache_alloc(cache);
> > +               pud_populate(NULL, pud, pmd);
> > +               get_page(virt_to_page(pud));
> > +       }
> > +
> > +       pmd = pmd_offset(pud, addr);
> > +
> > +       /*
> > +        * 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)
> > @@ -442,7 +518,7 @@ static int stage2_set_pte(struct kvm *kvm, struct kvm_mmu_memory_cache *cache,
> > 
> >         pmd = pmd_offset(pud, addr);
> > 
> > -       /* Create 2nd stage page table mapping - Level 2 */
> > +       /* Create 2nd stage page mappings - Level 2 */
> >         if (pmd_none(*pmd)) {
> >                 if (!cache)
> >                         return 0; /* ignore calls from kvm_set_spte_hva */
> > @@ -508,16 +584,53 @@ out:
> >         return ret;
> >  }
> > 
> > +static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
> > +{
> > +       pfn_t pfn = *pfnp;
> > +       gfn_t gfn = *ipap >> PAGE_SHIFT;
> > +
> > +       if (PageTransCompound(pfn_to_page(pfn))) {
> > +               unsigned long mask;
> > +               /*
> > +                * mmu_notifier_retry was successful and we hold the
> > +                * mmu_lock here, so the pmd can't become splitting
> > +                * from under us, and in turn
> > +                * __split_huge_page_refcount() can't run from under
> > +                * us and we can safely transfer the refcount from
> > +                * PG_tail to PG_head as we switch the pfn from tail to
> > +                * head.
> > +                */
> 
> -ECANTPARSE. Well, I sort of can, but this deserves a clearer explanation.
> 

I'll try to clarify.  (BTW. I stole this comment from Avi, blame the
both of us :))

> > +               mask = (PMD_SIZE / PAGE_SIZE) - 1;
> 
> 		mask = PTRS_PER_PMD -1;
> 
> > +               VM_BUG_ON((gfn & mask) != (pfn & mask));
> > +               if (pfn & mask) {
> > +                       gfn &= ~mask;
> 
> This doesn't seem to be used later on.
> 
> > +                       *ipap &= ~(PMD_SIZE - 1);
> 
> 			*ipap &= ~PMD_MASK;
> 

ack to all three

> > +                       kvm_release_pfn_clean(pfn);
> > +                       pfn &= ~mask;
> > +                       kvm_get_pfn(pfn);
> > +                       *pfnp = pfn;
> > +               }
> 
> 
> 
> > +               return true;
> > +       }
> > +
> > +       return false;
> > +}
> > +
> >  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;
> > +       unsigned long psize;
> > 
> >         write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
> >         if (fault_status == FSC_PERM && !write_fault) {
> > @@ -525,6 +638,27 @@ 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 */
> > +       down_read(&current->mm->mmap_sem);
> > +       vma = find_vma_intersection(current->mm, hva, hva + 1);
> > +       if (is_vm_hugetlb_page(vma)) {
> > +               hugetlb = true;
> > +               hva &= PMD_MASK;
> > +               gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
> > +               psize = PMD_SIZE;
> > +       } else {
> > +               psize = PAGE_SIZE;
> > +               if (vma->vm_start & ~PMD_MASK)
> > +                       force_pte = true;
> > +       }
> > +       up_read(&current->mm->mmap_sem);
> > +
> > +       pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
> > +       if (is_error_pfn(pfn))
> > +               return -EFAULT;
> 
> How does this work with respect to the comment that talks about reading
> mmu_seq before calling gfp_to_pfn_prot? Either the comment is wrong, or
> we read this too early.
> 

It doesn't, the gfn_to_pfn_prot call should be moved below the smp_rmb,
I must have simply messed this up when rebasing the patch.  Nice catch!

> > +       coherent_icache_guest_page(kvm, hva, psize);
> > +
> >         /* We need minimum second+third level pages */
> >         ret = mmu_topup_memory_cache(memcache, 2, KVM_NR_MEM_OBJS);
> >         if (ret)
> > @@ -542,26 +676,34 @@ 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);
> > -       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 && !force_pte)
> > +               hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
> 
> How do we ensure that there is no race between this pte being promoted
> to a pmd and another page allocation in the same pmd somewhere else in
> the system? We only hold the kvm lock here, so there must be some extra
> implicit guarantee somewhere...
> 

Steve answered this one, but the point is that any page in this pmd
cannot be allocated from anywhere, because those pages are not free.  At
this point, if the anon user page is mapped as a THP, it will stay as
such until we unlock the mmu_lock.

> > +       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);
> > +               }
> > +               ret = stage2_set_pmd(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);
> > +               }
> > +               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;
> >  }
> > 
> >  /**
> > @@ -630,7 +772,7 @@ 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;
> > +}
> > +
> >  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();
> 
> As a general comment about this patch, I think having both transparent
> pages *and* hugetlbfs support in the same patch makes it fairly hard to
> read.
> 
> I understand that is is actually convenient as most of the code is
> shared, but I think it would make it easier to read if the patch was
> split in two: first the basic hugetlb support, and then the THP madness.
> 
> What do you think?
> 
Sure, I can split them up.  I'm going to send out a v2 with the split
patches so you can read that in its completeness instead of the
fragments I posted above.  I can always spin a v3 if you have more
comments, though I still hope to get this in for the next merge window.

Thanks for the review!
-Christoffer