Subject: [PATCH v2 27/30] KVM: arm64: Move device mapping management into kvm_s2_fault_pin_pfn()

From: Marc Zyngier <[email-masked]>
Date: Fri, 27 Mar 2026 11:36:15 +0000

Attributes computed for devices are computed very late in the fault
handling process, meanning they are mutable for that long.

Introduce both 'device' and 'map_non_cacheable' attributes to the
vma_info structure, allowing that information to be set in stone
earlier, in kvm_s2_fault_pin_pfn().

Tested-by: Fuad Tabba <[email-masked]>
Reviewed-by: Fuad Tabba <[email-masked]>
Reviewed-by: Suzuki K Poulose <[email-masked]>
Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm64/kvm/mmu.c | 52 ++++++++++++++++++++++++--------------------
 1 file changed, 29 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 61b979365c6ee..23245ee7b1ec2 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1656,9 +1656,11 @@ struct kvm_s2_fault_vma_info {
 	struct page	*page;
 	kvm_pfn_t	pfn;
 	gfn_t		gfn;
+	bool		device;
 	bool		mte_allowed;
 	bool		is_vma_cacheable;
 	bool		map_writable;
+	bool		map_non_cacheable;
 };
 
 static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
@@ -1728,7 +1730,6 @@ static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
 }
 
 struct kvm_s2_fault {
-	bool s2_force_noncacheable;
 	enum kvm_pgtable_prot prot;
 };
 
@@ -1738,7 +1739,6 @@ static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
 }
 
 static int kvm_s2_fault_get_vma_info(const struct kvm_s2_fault_desc *s2fd,
-				     struct kvm_s2_fault *fault,
 				     struct kvm_s2_fault_vma_info *s2vi)
 {
 	struct vm_area_struct *vma;
@@ -1794,12 +1794,11 @@ static gfn_t get_canonical_gfn(const struct kvm_s2_fault_desc *s2fd,
 }
 
 static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
-				struct kvm_s2_fault *fault,
 				struct kvm_s2_fault_vma_info *s2vi)
 {
 	int ret;
 
-	ret = kvm_s2_fault_get_vma_info(s2fd, fault, s2vi);
+	ret = kvm_s2_fault_get_vma_info(s2fd, s2vi);
 	if (ret)
 		return ret;
 
@@ -1814,16 +1813,6 @@ static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
 		return -EFAULT;
 	}
 
-	return 1;
-}
-
-static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
-				     struct kvm_s2_fault *fault,
-				     const struct kvm_s2_fault_vma_info *s2vi)
-{
-	struct kvm *kvm = s2fd->vcpu->kvm;
-	bool writable = s2vi->map_writable;
-
 	/*
 	 * Check if this is non-struct page memory PFN, and cannot support
 	 * CMOs. It could potentially be unsafe to access as cacheable.
@@ -1842,8 +1831,10 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 			 * S2FWB and CACHE DIC are mandatory to avoid the need for
 			 * cache maintenance.
 			 */
-			if (!kvm_supports_cacheable_pfnmap())
+			if (!kvm_supports_cacheable_pfnmap()) {
+				kvm_release_faultin_page(s2fd->vcpu->kvm, s2vi->page, true, false);
 				return -EFAULT;
+			}
 		} else {
 			/*
 			 * If the page was identified as device early by looking at
@@ -1855,9 +1846,24 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 			 * In both cases, we don't let transparent_hugepage_adjust()
 			 * change things at the last minute.
 			 */
-			fault->s2_force_noncacheable = true;
+			s2vi->map_non_cacheable = true;
 		}
-	} else if (memslot_is_logging(s2fd->memslot) && !kvm_is_write_fault(s2fd->vcpu)) {
+
+		s2vi->device = true;
+	}
+
+	return 1;
+}
+
+static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
+				     struct kvm_s2_fault *fault,
+				     const struct kvm_s2_fault_vma_info *s2vi)
+{
+	struct kvm *kvm = s2fd->vcpu->kvm;
+	bool writable = s2vi->map_writable;
+
+	if (!s2vi->device && memslot_is_logging(s2fd->memslot) &&
+	    !kvm_is_write_fault(s2fd->vcpu)) {
 		/*
 		 * Only actually map the page as writable if this was a write
 		 * fault.
@@ -1865,7 +1871,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 		writable = false;
 	}
 
-	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && fault->s2_force_noncacheable)
+	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && s2vi->map_non_cacheable)
 		return -ENOEXEC;
 
 	/*
@@ -1888,7 +1894,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu))
 		fault->prot |= KVM_PGTABLE_PROT_X;
 
-	if (fault->s2_force_noncacheable)
+	if (s2vi->map_non_cacheable)
 		fault->prot |= (s2vi->vm_flags & VM_ALLOW_ANY_UNCACHED) ?
 			       KVM_PGTABLE_PROT_NORMAL_NC : KVM_PGTABLE_PROT_DEVICE;
 	else if (cpus_have_final_cap(ARM64_HAS_CACHE_DIC))
@@ -1897,7 +1903,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 	if (s2fd->nested)
 		adjust_nested_exec_perms(kvm, s2fd->nested, &fault->prot);
 
-	if (!kvm_s2_fault_is_perm(s2fd) && !fault->s2_force_noncacheable && kvm_has_mte(kvm)) {
+	if (!kvm_s2_fault_is_perm(s2fd) && !s2vi->map_non_cacheable && kvm_has_mte(kvm)) {
 		/* Check the VMM hasn't introduced a new disallowed VMA */
 		if (!s2vi->mte_allowed)
 			return -EFAULT;
@@ -1937,7 +1943,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 	 * backed by a THP and thus use block mapping if possible.
 	 */
 	if (mapping_size == PAGE_SIZE &&
-	    !(s2vi->max_map_size == PAGE_SIZE || fault->s2_force_noncacheable)) {
+	    !(s2vi->max_map_size == PAGE_SIZE || s2vi->map_non_cacheable)) {
 		if (perm_fault_granule > PAGE_SIZE) {
 			mapping_size = perm_fault_granule;
 		} else {
@@ -1951,7 +1957,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 		}
 	}
 
-	if (!perm_fault_granule && !fault->s2_force_noncacheable && kvm_has_mte(kvm))
+	if (!perm_fault_granule && !s2vi->map_non_cacheable && kvm_has_mte(kvm))
 		sanitise_mte_tags(kvm, pfn, mapping_size);
 
 	/*
@@ -2020,7 +2026,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 	 * Let's check if we will get back a huge page backed by hugetlbfs, or
 	 * get block mapping for device MMIO region.
 	 */
-	ret = kvm_s2_fault_pin_pfn(s2fd, &fault, &s2vi);
+	ret = kvm_s2_fault_pin_pfn(s2fd, &s2vi);
 	if (ret != 1)
 		return ret;
 
-- 
2.47.3