Subject: [PATCH 4/6] KVM: arm64/mmu: avoid struct page in MMU

From: David Stevens <[email-masked]>
Date: Thu, 24 Jun 2021 12:57:47 +0900

From: David Stevens <[email-masked]>

Avoid converting pfns returned by follow_fault_pfn to struct pages to
transiently take a reference. The reference was originally taken to
match the reference taken by gup. However, pfns returned by
follow_fault_pfn may not have a struct page set up for reference
counting.

Signed-off-by: David Stevens <[email-masked]>
---
 arch/arm64/kvm/mmu.c | 43 +++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 896b3644b36f..a741972cb75f 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -779,17 +779,17 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
  */
 static unsigned long
 transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
-			    unsigned long hva, kvm_pfn_t *pfnp,
+			    unsigned long hva, struct kvm_pfn_page *pfnpgp,
 			    phys_addr_t *ipap)
 {
-	kvm_pfn_t pfn = *pfnp;
+	kvm_pfn_t pfn = pfnpgp->pfn;
 
 	/*
 	 * Make sure the adjustment is done only for THP pages. Also make
 	 * sure that the HVA and IPA are sufficiently aligned and that the
 	 * block map is contained within the memslot.
 	 */
-	if (kvm_is_transparent_hugepage(pfn) &&
+	if (pfnpgp->page && kvm_is_transparent_hugepage(pfn) &&
 	    fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
 		/*
 		 * The address we faulted on is backed by a transparent huge
@@ -810,10 +810,11 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
 		 * page accordingly.
 		 */
 		*ipap &= PMD_MASK;
-		kvm_release_pfn_clean(pfn);
+		put_page(pfnpgp->page);
 		pfn &= ~(PTRS_PER_PMD - 1);
-		kvm_get_pfn(pfn);
-		*pfnp = pfn;
+		pfnpgp->pfn = pfn;
+		pfnpgp->page = pfn_to_page(pfnpgp->pfn);
+		get_page(pfnpgp->page);
 
 		return PMD_SIZE;
 	}
@@ -836,7 +837,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	struct vm_area_struct *vma;
 	short vma_shift;
 	gfn_t gfn;
-	kvm_pfn_t pfn;
+	struct kvm_pfn_page pfnpg;
 	bool logging_active = memslot_is_logging(memslot);
 	unsigned long fault_level = kvm_vcpu_trap_get_fault_level(vcpu);
 	unsigned long vma_pagesize, fault_granule;
@@ -933,17 +934,16 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	 */
 	smp_rmb();
 
-	pfn = kvm_pfn_page_unwrap(__gfn_to_pfn_memslot(memslot, gfn, false,
-						       NULL, write_fault,
-						       &writable, NULL));
-	if (pfn == KVM_PFN_ERR_HWPOISON) {
+	pfnpg = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
+				     write_fault, &writable, NULL);
+	if (pfnpg.pfn == KVM_PFN_ERR_HWPOISON) {
 		kvm_send_hwpoison_signal(hva, vma_shift);
 		return 0;
 	}
-	if (is_error_noslot_pfn(pfn))
+	if (is_error_noslot_pfn(pfnpg.pfn))
 		return -EFAULT;
 
-	if (kvm_is_device_pfn(pfn)) {
+	if (kvm_is_device_pfn(pfnpg.pfn)) {
 		device = true;
 		force_pte = true;
 	} else if (logging_active && !write_fault) {
@@ -968,16 +968,16 @@ 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);
+							   &pfnpg, &fault_ipa);
 	if (writable)
 		prot |= KVM_PGTABLE_PROT_W;
 
 	if (fault_status != FSC_PERM && !device)
-		clean_dcache_guest_page(pfn, vma_pagesize);
+		clean_dcache_guest_page(pfnpg.pfn, vma_pagesize);
 
 	if (exec_fault) {
 		prot |= KVM_PGTABLE_PROT_X;
-		invalidate_icache_guest_page(pfn, vma_pagesize);
+		invalidate_icache_guest_page(pfnpg.pfn, vma_pagesize);
 	}
 
 	if (device)
@@ -994,20 +994,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		ret = kvm_pgtable_stage2_relax_perms(pgt, fault_ipa, prot);
 	} else {
 		ret = kvm_pgtable_stage2_map(pgt, fault_ipa, vma_pagesize,
-					     __pfn_to_phys(pfn), prot,
+					     __pfn_to_phys(pfnpg.pfn), prot,
 					     memcache);
 	}
 
 	/* Mark the page dirty only if the fault is handled successfully */
 	if (writable && !ret) {
-		kvm_set_pfn_dirty(pfn);
+		if (pfnpg.page)
+			kvm_set_pfn_dirty(pfnpg.pfn);
 		mark_page_dirty_in_slot(kvm, memslot, gfn);
 	}
 
 out_unlock:
 	spin_unlock(&kvm->mmu_lock);
-	kvm_set_pfn_accessed(pfn);
-	kvm_release_pfn_clean(pfn);
+	if (pfnpg.page) {
+		kvm_set_pfn_accessed(pfnpg.pfn);
+		put_page(pfnpg.page);
+	}
 	return ret != -EAGAIN ? ret : 0;
 }
 
-- 
2.32.0.93.g670b81a890-goog