Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

Pull kvm fixes from Paolo Bonzini:
 "KVM GUEST_MEMFD fixes for 6.8:

   - Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY
     to avoid creating an inconsistent ABI (KVM_MEM_GUEST_MEMFD is not
     writable from userspace, so there would be no way to write to a
     read-only guest_memfd).

   - Update documentation for KVM_SW_PROTECTED_VM to make it abundantly
     clear that such VMs are purely for development and testing.

   - Limit KVM_SW_PROTECTED_VM guests to the TDP MMU, as the long term
     plan is to support confidential VMs with deterministic private
     memory (SNP and TDX) only in the TDP MMU.

   - Fix a bug in a GUEST_MEMFD dirty logging test that caused false
     passes.

  x86 fixes:

   - Fix missing marking of a guest page as dirty when emulating an
     atomic access.

   - Check for mmu_notifier invalidation events before faulting in the
     pfn, and before acquiring mmu_lock, to avoid unnecessary work and
     lock contention with preemptible kernels (including
     CONFIG_PREEMPT_DYNAMIC in non-preemptible mode).

   - Disable AMD DebugSwap by default, it breaks VMSA signing and will
     be re-enabled with a better VM creation API in 6.10.

   - Do the cache flush of converted pages in svm_register_enc_region()
     before dropping kvm->lock, to avoid a race with unregistering of
     the same region and the consequent use-after-free issue"

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  SEV: disable SEV-ES DebugSwap by default
  KVM: x86/mmu: Retry fault before acquiring mmu_lock if mapping is changing
  KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region()
  KVM: selftests: Add a testcase to verify GUEST_MEMFD and READONLY are exclusive
  KVM: selftests: Create GUEST_MEMFD for relevant invalid flags testcases
  KVM: x86/mmu: Restrict KVM_SW_PROTECTED_VM to the TDP MMU
  KVM: x86: Update KVM_SW_PROTECTED_VM docs to make it clear they're a WIP
  KVM: Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY
  KVM: x86: Mark target gfn of emulated atomic instruction as dirty

1 files changed, 26 insertions, 0 deletions

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 7e7fd25b09b3..179df96b20f8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2031,6 +2031,32 @@ static inline int mmu_invalidate_retry_gfn(struct kvm *kvm,
 		return 1;
 	return 0;
 }
+
+/*
+ * This lockless version of the range-based retry check *must* be paired with a
+ * call to the locked version after acquiring mmu_lock, i.e. this is safe to
+ * use only as a pre-check to avoid contending mmu_lock.  This version *will*
+ * get false negatives and false positives.
+ */
+static inline bool mmu_invalidate_retry_gfn_unsafe(struct kvm *kvm,
+						   unsigned long mmu_seq,
+						   gfn_t gfn)
+{
+	/*
+	 * Use READ_ONCE() to ensure the in-progress flag and sequence counter
+	 * are always read from memory, e.g. so that checking for retry in a
+	 * loop won't result in an infinite retry loop.  Don't force loads for
+	 * start+end, as the key to avoiding infinite retry loops is observing
+	 * the 1=>0 transition of in-progress, i.e. getting false negatives
+	 * due to stale start+end values is acceptable.
+	 */
+	if (unlikely(READ_ONCE(kvm->mmu_invalidate_in_progress)) &&
+	    gfn >= kvm->mmu_invalidate_range_start &&
+	    gfn < kvm->mmu_invalidate_range_end)
+		return true;
+
+	return READ_ONCE(kvm->mmu_invalidate_seq) != mmu_seq;
+}
 #endif
 
 #ifdef CONFIG_HAVE_KVM_IRQ_ROUTING