From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f198.google.com (mail-pl1-f198.google.com [209.85.214.198]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E808B51475F for ; Mon, 21 Sep 2026 21:06:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.198 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790024787; cv=none; b=TsljrmM5cQzIq6Xg3gnNzdfoeShUujYFHJJC+SAPQsXrulmc4NqgYjuenMiGNYxpf/BKxpPi2XF5209L760atwcy13mcZ5eE/CFz8c5SdAdD2Kba9SqDKt1aWOiNjCxvM5GxwMRTpLG50uC3MAe1NyZwXaacT7KowIOiGwtj8AE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790024787; c=relaxed/simple; bh=a/Ta7ugmnfE2olxYhVTUQxbez2+HQ62mFKA5+uOWAR8=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=tKYZUiU9yduKuslefXU7MNT0tuWKpadf8clYTdUAyHK29gRvo026z+p3j2RL1Jzv/lk7dUGMFPF3BsgfhigsCxWeGWtVAe8RWx8B5sXKAcduc5ny49Yfkkd/CONkQ0zyu0//BwyBZiS0Epp8bgKsL/OfGVjmkEu4k7v9p3lBf4Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=OaViMNEa; arc=none smtp.client-ip=209.85.214.198 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="OaViMNEa" Received: by mail-pl1-f198.google.com with SMTP id d9443c01a7336-2d94f086fedso49973305ad.1 for ; Mon, 21 Sep 2026 14:06:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1790024785; x=1790629585; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:from:to:cc:subject:date:message-id :reply-to:content-type; bh=e5qHde0DG0iGDJnHfYl3SHserU3q1V+JrrCFiXRle6c=; b=OaViMNEaC5skwUOwyqd3bDKWSZ+QRJ38McApbcbvck912eWXdoBGysYXzxUs3aHJtm A21BF4tlL1Fs/7/pHRyT0YpvmGoSK3S7qrsxe70seeEs+LF6N0QXCXoaeNB0xBL6xMjN +HRHDBikrroKmRJPbJvbW1RmLFHrasDWfDCb8BaUp7IoYSS62ayW/aqv4aB2FPBlqDwz cxRBgjIc+oiPoqs/Gmgop48UY8Z6OIvMNG+pgddBvsu21klCJdBWiDJW/Z/EhxATEB1t F2YC7Dx1scU/z+eGNf101jBcY/qgxhcqPuRzhYY+fmQfsF/85hLivnqwMQITnqv8bK3u bTRQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790024785; x=1790629585; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:reply-to:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to:content-type; bh=e5qHde0DG0iGDJnHfYl3SHserU3q1V+JrrCFiXRle6c=; b=HlVhBU++sryo4QqYjYVkAfTvtO3VW0myHuMe7n/YzQhzbrVS0n1CybaoZaHTdFsrgg b2TmR0uMFDzIjdbBh6yx/lPqDkNdv04pXK+KRf+mCych4+PU8J7pJYYd1tR7RM1acU7Y 7UP+AGn08XDlHfro1GLTR0Tnf3SqBau+qhMuL1koGUbmipiMk5lxLDvDdbH5BM2URPNK Eq2vLTtxpvATiJAneN0xBy2gY7MLkryLcEQMxLe3eVeird7hYlE2Pf32zpXDGzy8VbFW Kr3axvTfy2O8Im2QM7MeSKl89APfeangszdrjxazyF61lZ/n1Rr+OuQg9wTBLdcFxPug CDOA== X-Forwarded-Encrypted: i=1; AKwUvBy0Y0V1Lx3FdUo9yJlHONElWxs3uez83HIpaoiOVAPwGwsSslx256hNCks4w6UFDDJba9U=@vger.kernel.org X-Gm-Message-State: AFuF++mNOaFGCsjS8H2hT9Berf9qxJKrX0301OqcbMlHxD8HdGVd+Q5c LSvAhIUspjYFC0QunAGlwljVDTlDtapclmPAx2ApChWD3NWgE83U6TXAd95+yTVOJo/r3ixnyPu fhDf1Mw== X-Received: from plrp17.prod.google.com ([2002:a17:902:b091:b0:2db:1a39:c145]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:1a90:b0:2dd:3d1a:6958 with SMTP id d9443c01a7336-2ddb1ab3a86mr181174905ad.6.1790024784833; Mon, 21 Sep 2026 14:06:24 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 21 Sep 2026 14:06:14 -0700 In-Reply-To: <20260921210616.1024168-1-seanjc@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260921210616.1024168-1-seanjc@google.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260921210616.1024168-4-seanjc@google.com> Subject: [PATCH v4 3/5] KVM: Only bind memslot to guest_memfd instance for CREATE operations From: Sean Christopherson To: Paolo Bonzini , Sean Christopherson Cc: David Hildenbrand , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Stefan Teodorescu , Dennis Tighe , Sashiko Bot , Ackerley Tng , Yan Zhao Content-Type: text/plain; charset="UTF-8" For additional defense-in-depth, and to avoid having to handle impossible unwind scenarios when binding to a memslot fails, bind a memslot to a gmem instance only when for CREATE operations, i.e. don't attempt to establish a binding for MOVE and FLAGS_ONLY operations. And when FLAGS_ONLY operations are eventually supported (this is currently all dead code), creating a new binding would be incorrect; KVM instead needs to do a 1:1 replacement of the existing binding, i.e. FLAGS_ONLY will need its own dedicated handling. Update the relevant TODO to make a better guess as to what needs to be done to support toggling dirty logging for guest_memfd memslots. Because it's dead code, no functional change intended. Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 24cf96840827..b417b1f7095f 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1752,10 +1752,10 @@ static void kvm_commit_memory_region(struct kvm *kvm, kvm_destroy_dirty_bitmap(old); /* - * Unbind the guest_memfd instance as needed; the @new slot has - * already created its own binding. TODO: Drop the WARN when - * dirty logging guest_memfd memslots is supported. Until then, - * flags-only changes on guest_memfd slots should be impossible. + * TODO: Drop the WARN and do the unbind() call only for MOVE + * when dirty logging guest_memfd memslots is supported. Until + * then, flags-only changes on guest_memfd slots should also be + * impossible; unbind the old memslot for defense-in-depth. */ if (WARN_ON_ONCE(old->flags & KVM_MEM_GUEST_MEMFD)) kvm_gmem_unbind(old); @@ -2116,7 +2116,7 @@ static int kvm_set_memory_region(struct kvm *kvm, new->npages = npages; new->flags = mem->flags; new->userspace_addr = mem->userspace_addr; - if (mem->flags & KVM_MEM_GUEST_MEMFD) { + if (change == KVM_MR_CREATE && (mem->flags & KVM_MEM_GUEST_MEMFD)) { r = kvm_gmem_bind(kvm, new, mem->guest_memfd, mem->guest_memfd_offset); if (r) goto out; -- 2.55.0.1082.g2b9226bbc0-goog