KVM: ARM: Support hugetlbfs backed huge pages

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.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

1 files changed, 131 insertions, 38 deletions

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index b0de86b56c13..745d8b1630cc 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;
         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 +596,15 @@ 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;
+        }
+        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 +622,38 @@ 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 +722,7 @@ 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: