[PATCH RFC 03/10] KVM: guest_memfd: Avoid conditional mmu_lock acquisition
From: Marco Elver <elver@google.com>
Date: 2026-09-10 16:24:01
Also in:
kvm, lkml
Subsystem:
kernel virtual machine (kvm), kvm guest_memfd, the rest · Maintainers:
Paolo Bonzini, Sean Christopherson, Linus Torvalds
Refactor __kvm_gmem_invalidate_start() to check for present bindings upfront via xa_find() instead of tracking found memslots inside the range iteration with a 'found_memslot' flag and conditionally acquiring and releasing KVM's mmu_lock. Eliminating the conditional locking inside the loop simplifies control flow, ensures lock scoping is straightforward, and subsequently allows Clang context analysis to verify that mmu_lock is held unconditionally across kvm_mmu_unmap_gfn_range(). No functional change intended. Signed-off-by: Marco Elver <elver@google.com> --- virt/kvm/guest_memfd.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 625e62e1a031..896f3b076562 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c@@ -124,10 +124,16 @@ static void __kvm_gmem_invalidate_start(struct gmem_file *f, pgoff_t start, pgoff_t end, enum kvm_gfn_range_filter attr_filter) { - bool flush = false, found_memslot = false; + bool flush = false; struct kvm_memory_slot *slot; struct kvm *kvm = f->kvm; - unsigned long index; + pgoff_t index = start; + + if (!xa_find(&f->bindings, &index, end - 1, XA_PRESENT)) + return; + + KVM_MMU_LOCK(kvm); + kvm_mmu_invalidate_start(kvm); xa_for_each_range(&f->bindings, index, slot, start, end - 1) { pgoff_t pgoff = slot->gmem.pgoff;
@@ -140,13 +146,6 @@ static void __kvm_gmem_invalidate_start(struct gmem_file *f, pgoff_t start, .attr_filter = attr_filter, }; - if (!found_memslot) { - found_memslot = true; - - KVM_MMU_LOCK(kvm); - kvm_mmu_invalidate_start(kvm); - } - flush |= kvm_mmu_unmap_gfn_range(kvm, &gfn_range); #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
@@ -157,8 +156,7 @@ static void __kvm_gmem_invalidate_start(struct gmem_file *f, pgoff_t start, if (flush) kvm_flush_remote_tlbs(kvm); - if (found_memslot) - KVM_MMU_UNLOCK(kvm); + KVM_MMU_UNLOCK(kvm); } static void kvm_gmem_invalidate_start(struct inode *inode, pgoff_t start,
--
2.55.0.1003.g10538fe699-goog