From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-io1-f74.google.com (mail-io1-f74.google.com [209.85.166.74]) (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 17A6A4A00 for ; Wed, 7 May 2025 00:03:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.166.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746576229; cv=none; b=jEWKCZhXNGhU/ofpxziJFfNGIe+didUSQ/qgoj8dyEdywAkIEWkN6ffYhyNCwjB+04tdvG7kfLCDoRUqTQAce5wHM322lhhBMDzUX/CGs/uWlaJBvC4xpv3JTJ1NDdO6MbyKf1eeQsdcJpeFTLx4YlkaywxSGRHl1ahqAS1KmDA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746576229; c=relaxed/simple; bh=VrNSbBLOCr7NEwSbl8xm2RoaraSzVHKq/zWcp73SSJo=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=aAFbuHPQ4bn/HU0u4wq/bHwef6Cv3bpB9s6VWy1gvVOsmL4gjoT1kq0t+Uz3BB0DHZAFvh30OaGd8+k4Fo2EhChLs3zqUy8QU3kwwADevLXyN7NtHUj23zos9YY23mOk0mGf4AkJ3++ILrB/jGQ8jU2++JWj3Ixt5D7ctqvjtE0= 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=y7uHFtvT; arc=none smtp.client-ip=209.85.166.74 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="y7uHFtvT" Received: by mail-io1-f74.google.com with SMTP id ca18e2360f4ac-86195b64df7so1124577739f.2 for ; Tue, 06 May 2025 17:03:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1746576227; x=1747181027; darn=vger.kernel.org; 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=y7uHFtvTiHiaBSNpWx5YxO1QVW4x6TEKij8Uib+yD5dev3coUfLCtILfO7amthO1f1 IME0961vjuEmVuYbjkGzrkFeCKlGwLJe0ZwGae3vQNSc/RXoBCiojN7+e8wJVzXbuqt7 HUOyLSMg6SdPLLu62AIB+aAfNuugRsloknUoYZT6gh6JMlUXfxkWGml0MNW8pAAwxAK/ RvRDCrvdShYLvs41etEwt7Kq7DIllQhLh/TzYg0RURmG4Fa0POHU5qx8PS2CU3m8XZhr RyA2NelFFgeE9z+xqngEgI8EswVm1QbU0v7yHbkhsH0/35wC9fHNd4X8nvjaN8Ps4I/+ ns4Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746576227; x=1747181027; 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=ni4e5RyKw3A5pNY7ymIX52A9lCRo8jIffzpFS2rSrgkoLhheeNKHdhk7CAmyEaJhZJ 0mGA69zz+5NUVuAoC/8nNAK9EF8Cd/0aWAb02a1rF2wUZBeJg3t4nXM0mt59uUT1svrZ Y+dOxSXujyzUPiLsRI2eugcCuJEtHgSq2go5WInlwawGZjgezUSVI4PFlPzLDH3uFwCk BiDFdxvofw8fuv93/iaZuETlm580TOk0hJ1ssNaMoBTnSWyypcoLh08WjP35+rRsvV1i CeZUVHHOQsoVUEM5Dvaee/EgBCyv/b5dC4ZbhKtD5IWjdwRXwKx3r2ftgKaczY2P/TCu itOQ== X-Forwarded-Encrypted: i=1; AJvYcCUyRfbwjBBCt5pE0jJd/d/T3sDerCgn5iBnxhMd7wgZrudkqjzMs5ismevM51ubaXNAsNg=@vger.kernel.org X-Gm-Message-State: AOJu0YxvkzOXSkzfEp38kDS4LTAcqwNh+q77tdjNIduxQlV3amMn2ktm vLIARiLraGlOa/lIMOxUdmqqVRwyNvezDPV6LR2AOpbRRf4n/fohmv0dlFVUVPCxIpDSRa3+i4r 4ug== 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: kvm@vger.kernel.org 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 >