From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-il1-f201.google.com (mail-il1-f201.google.com [209.85.166.201]) (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 E12E74B1E7B for ; Wed, 7 May 2025 00:03:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.166.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746576230; cv=none; b=CIKsNIjye8PvqL0P3bNv2BGggGGqT41ztx/QRW8p7YQzUHp4+KAFi8jKgk41tC3cQZaidsvzs8dord6bm1/eZNOafVSKRqYcIaJnPXLBH+vF4FqChwMEIcK5ZOi12/iroyNB2vcYR1dlbxq/MfUTzIMPSmq10YnQMlf69gcSPHg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746576230; c=relaxed/simple; bh=VrNSbBLOCr7NEwSbl8xm2RoaraSzVHKq/zWcp73SSJo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=HcR7Av/F8HxXZZ+0M/iV+Wtbpvlu7e76whkS53f9nzuh51Zf6DetSc0XRSo/BfyXO+z8tB36teWl7qh3O7at/0FU2IOslTUkkinQRmnlru+92T4If+GKd3XN1heP0zlKF3WyrOZNg0EC/F9HRik0E0mgqBQfklotnVWg3wPUHKo= 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=IZapz6gV; arc=none smtp.client-ip=209.85.166.201 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="IZapz6gV" Received: by mail-il1-f201.google.com with SMTP id e9e14a558f8ab-3d90a7e86f7so148337765ab.2 for ; Tue, 06 May 2025 17:03:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1746576228; x=1747181028; darn=lists.linux.dev; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=5+m6HPDtb0R18pUg/qJCD2U+j03ktvX2ktaHxXO8cS8=; b=IZapz6gV15Jm8vVyOQzCJsDJhasM1gIcHps0iMtWUl5KYUjBlJBdJ4Rf3XS74CYF+P 9oGKIzGFaDm+RlyPLvY5mBLYI5VsiEmb3X78HmD1337BDz0fGglbrNFN4qz/eW/ucCHa sABZhrdHsghzwJLqGOTRiVWxeZCagv68bmDNH7FcM9oQGUE2/pjA1UEkTJit65dmQ2nu yAmCRbEF8/x+T8G061H9sAiMphmDm/CcduE8x+Uk1ArcxGE0DB6hItxZKPpVDtA2MSWB tJ6xv12ceSJUxX45ZwAGTJNh6gl3N8kMBrPn1CNh1raXKS8S7oKva7i2jOl4kC/XYfF1 9cmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746576228; x=1747181028; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=5+m6HPDtb0R18pUg/qJCD2U+j03ktvX2ktaHxXO8cS8=; b=oyLb1KeaeJG8377cauH+Ij57mWTTv0/b01PQnAto6IbDUSz4ycWT8WnBi/NO3fgAzf W1YzYHpIUcl0uZVPBWNVUki9u/A8WBd1ta9jVWXlEEY151kYS4cmpBU+IOY97qfcNYpU FtloofZwyTAbUQMAGZNcTJok5jL1Q8gEHLpaTL3dfyr4k6wwWlxt2WPEtjnkebo1DKDm XeNAPflVSe7SkYpYNESdEY0p6WxuBlemcNqviRRpaFeb+xsmyYAT/scTfvDRjR3J0gSb u6EC0Nb9zzVthrRWQw9VsT9uqNIia+3onF/lyYJxLUJktKUi4CXO+X9yI8xFyg2oEpHx /qbg== X-Forwarded-Encrypted: i=1; AJvYcCURrAMaOaHZ6zvpnpziFyenNAMGz/jBqr4fvLjB0emUblKWWQODP7bW6WGz8nRbAWRgvQtfRkk=@lists.linux.dev X-Gm-Message-State: AOJu0Yy50NzoNmVIivlKkz4UqCl4wYF+O42MWgyEau5mDVsA2aORokmn 5vOqX9iBftEuf18F/kdBNnvf31EAmzwxxbYA0iDL4ElCdOWFNV0rxQL3cH5LGTwDIGQGFXVfekr ntg== X-Google-Smtp-Source: AGHT+IG6Fxa93Bz0YoXvtTYguCqgLiKUWD1kixt49zVH2HtfKhQptZBHYIAFUFv7wo+hSUraRC2rqINWD4c= X-Received: from pjbnb1.prod.google.com ([2002:a17:90b:35c1:b0:30a:7c16:a1aa]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3d8c:b0:2f2:a664:df1a with SMTP id 98e67ed59e1d1-30aac156361mr2370837a91.2.1746576217154; Tue, 06 May 2025 17:03:37 -0700 (PDT) Date: Tue, 6 May 2025 17:03:35 -0700 In-Reply-To: <20250109204929.1106563-4-jthoughton@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250109204929.1106563-1-jthoughton@google.com> <20250109204929.1106563-4-jthoughton@google.com> Message-ID: Subject: Re: [PATCH v2 03/13] KVM: Allow late setting of KVM_MEM_USERFAULT on guest_memfd memslot From: Sean Christopherson To: James Houghton Cc: Paolo Bonzini , Jonathan Corbet , Marc Zyngier , Oliver Upton , Yan Zhao , Nikita Kalyazin , Anish Moorthy , Peter Gonda , Peter Xu , David Matlack , wei.w.wang@intel.com, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Content-Type: text/plain; charset="us-ascii" On Thu, Jan 09, 2025, James Houghton wrote: > Currently guest_memfd memslots can only be deleted. Slightly change the > logic to allow KVM_MR_FLAGS_ONLY changes when the only flag being > changed is KVM_MEM_USERFAULT. > > Signed-off-by: James Houghton > --- > virt/kvm/kvm_main.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 4bceae6a6401..882c1f7b4aa8 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -2015,9 +2015,6 @@ int __kvm_set_memory_region(struct kvm *kvm, > if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages) > return -EINVAL; > } else { /* Modify an existing slot. */ > - /* Private memslots are immutable, they can only be deleted. */ > - if (mem->flags & KVM_MEM_GUEST_MEMFD) > - return -EINVAL; > if ((mem->userspace_addr != old->userspace_addr) || > (npages != old->npages) || > ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) > @@ -2031,6 +2028,16 @@ int __kvm_set_memory_region(struct kvm *kvm, > return 0; > } > > + /* > + * Except for being able to set KVM_MEM_USERFAULT, private memslots are > + * immutable, they can only be deleted. > + */ > + if (mem->flags & KVM_MEM_GUEST_MEMFD && > + !(change == KVM_MR_CREATE || > + (change == KVM_MR_FLAGS_ONLY && > + (mem->flags ^ old->flags) == KVM_MEM_USERFAULT))) > + return -EINVAL; Oof. I don't even want to decipher this. Let's just drop the blankent immutable restriction, and simply say guest_memfd slots can't be MOVED. guest_memfd doesn't support RO memslots (and never will), and doesn't support dirty logging, so this is effectively dead code anyways. Then the diff is much nicer: @@ -2012,14 +2027,15 @@ static int kvm_set_memory_region(struct kvm *kvm, if ((kvm->nr_memslot_pages + npages) < kvm->nr_memslot_pages) return -EINVAL; } else { /* Modify an existing slot. */ - /* Private memslots are immutable, they can only be deleted. */ - if (mem->flags & KVM_MEM_GUEST_MEMFD) - return -EINVAL; if ((mem->userspace_addr != old->userspace_addr) || (npages != old->npages) || ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) return -EINVAL; + /* Moving a guest_memfd memslot isn't supported. */ + if (base_gfn != old->base_gfn && mem->flags & KVM_MEM_GUEST_MEMFD) + return -EINVAL; + if (base_gfn != old->base_gfn) change = KVM_MR_MOVE; else if (mem->flags != old->flags) > + > if ((change == KVM_MR_CREATE || change == KVM_MR_MOVE) && > kvm_check_memslot_overlap(slots, id, base_gfn, base_gfn + npages)) > return -EEXIST; > @@ -2046,7 +2053,7 @@ 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 (mem->flags & KVM_MEM_GUEST_MEMFD && change == KVM_MR_CREATE) { > r = kvm_gmem_bind(kvm, new, mem->guest_memfd, mem->guest_memfd_offset); > if (r) > goto out; > -- > 2.47.1.613.gc27f4b7a9f-goog >