linux-kernel - [PATCH v3 06/15] KVM: arm64: Add support for KVM userfault exits

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Message-ID: <20250618042424.330664-7-jthoughton@google.com>
Date: Wed, 18 Jun 2025 04:24:15 +0000
From: James Houghton <jthoughton@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, 
	Oliver Upton <oliver.upton@...ux.dev>
Cc: Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>, Yan Zhao <yan.y.zhao@...el.com>, 
	James Houghton <jthoughton@...gle.com>, Nikita Kalyazin <kalyazin@...zon.com>, 
	Anish Moorthy <amoorthy@...gle.com>, Peter Gonda <pgonda@...gle.com>, Peter Xu <peterx@...hat.com>, 
	David Matlack <dmatlack@...gle.com>, wei.w.wang@...el.com, kvm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev
Subject: [PATCH v3 06/15] KVM: arm64: Add support for KVM userfault exits

To support KVM userfault exits with arm64:

1. Force mappings to be 4K while KVM_MEM_USERFAULT is enabled.
2. Return -EFAULT when kvm_do_userfault() reports that the page is
   userfault (or that reading the bitmap failed).

kvm_arch_commit_memory_region() was written assuming that, for
KVM_MR_FLAGS_ONLY changes, KVM_MEM_LOG_DIRTY_PAGES must be being
toggled. This is no longer the case, so adjust the logic appropriately.

Signed-off-by: James Houghton <jthoughton@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/arm64/kvm/mmu.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 0c209f2e1c7b2..d75a6685d6842 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1548,7 +1548,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	 * logging_active is guaranteed to never be true for VM_PFNMAP
 	 * memslots.
 	 */
-	if (logging_active) {
+	if (logging_active || is_protected_kvm_enabled() ||
+	    kvm_is_userfault_memslot(memslot)) {
 		force_pte = true;
 		vma_shift = PAGE_SHIFT;
 	} else {
@@ -1637,6 +1638,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	mmu_seq = vcpu->kvm->mmu_invalidate_seq;
 	mmap_read_unlock(current->mm);
 
+	if (kvm_do_userfault(vcpu, &fault))
+		return -EFAULT;
+
 	pfn = __kvm_faultin_pfn(memslot, fault.gfn, fault.write ? FOLL_WRITE : 0,
 				&writable, &page);
 	if (pfn == KVM_PFN_ERR_HWPOISON) {
@@ -2134,15 +2138,19 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				   const struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
-	bool log_dirty_pages = new && new->flags & KVM_MEM_LOG_DIRTY_PAGES;
+	u32 old_flags = old ? old->flags : 0;
+	u32 new_flags = new ? new->flags : 0;
+
+	/* Nothing to do if not toggling dirty logging. */
+	if (!((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES))
+		return;
 
 	/*
 	 * At this point memslot has been committed and there is an
 	 * allocated dirty_bitmap[], dirty pages will be tracked while the
 	 * memory slot is write protected.
 	 */
-	if (log_dirty_pages) {
-
+	if (new_flags & KVM_MEM_LOG_DIRTY_PAGES) {
 		if (change == KVM_MR_DELETE)
 			return;
 
-- 
2.50.0.rc2.692.g299adb8693-goog