From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DC5E23BBFDC for ; Thu, 4 Jun 2026 22:27:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780612038; cv=none; b=TYqucFuUmGKuVjd0ERCHwJsn0pk8EODIPrDgCQdDJ+l6vnSxkdjIH+7pA7gCZF8rhzVyMAtUI7v0jZmft2fl34C9Wbr2iNcJfTf2N267OZB12+p/Ou4Nj7sAygUhkdq+Jv/ZJNmpWu/lc4IthyklUybnG7mTGVRjzZKBAx/GDTs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780612038; c=relaxed/simple; bh=FAzTBD6K/Z3MG0ycrZfsQXj1ITObrpAqAJRFlIK7KvE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QEW6Z8aPPNxb/bZ7HczN3bnL9j2ccF45lms4OW497/4Uy3hucqj0AcV+ngQMI+awMrwQiRzvArgXn3QmROrQqv+S/L7nMpBQLEi3YA0cu3KKVprRbXZ3nM87iNVM14K9Y5ISnOFkfhOdfbz38iJ9i7mlTUaIthwNp+mqIsD7Sgk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YY+PWJbq; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YY+PWJbq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D5E51F00893; Thu, 4 Jun 2026 22:27:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780612037; bh=F+Z44FQYE3kr39+LeJ1gbg5UpwtjtjiI6+HmJr0+Ky4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=YY+PWJbqFOW7MVHs2UWn9WKb/O3pLlrClAakAXKjMh1xBVdz51aK2XYVyhzzk/Yei cXqj142YHZuANKznAmo7xUOCxc4ZTt7Dy+D/wO+tGgjNiqwXzGB5QU9ecuKvvp9nz4 LbE/Lv0Y+XlDSqFM7RKgNC9riQq325Dcru28U6nmW+aFoMZuy74lafmpFek2sVgR7W +XcIOZgw97Xyw4BtM1x2fhEen2PUuQLHapOkKEnvXQ5OP8ZQKTBKDqU68RYY02L+wg 76UsarN/e2oiRjJjEsjwXPSlo11i3yzqpso1I9WLuesFGXP7ZT2J9L38eUo5UuE7VJ IKMbxFwuk0KkQ== Date: Thu, 4 Jun 2026 15:27:16 -0700 From: Oliver Upton To: Hyunwoo Kim Cc: maz@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, christoffer.dall@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev Subject: Re: [PATCH] KVM: arm64: Reallocate the nested_mmus array under the mmu_lock Message-ID: References: Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hi, The shortlog is very confusing, since "allocate behind $LOCK" is usually something alarming. Maybe instead: KVM: arm64: Reassign nested_mmus array behind mmu_lock On Fri, Jun 05, 2026 at 03:30:00AM +0900, Hyunwoo Kim wrote: > Code that walks kvm->arch.nested_mmus[] holds kvm->mmu_lock. By contrast, > kvm_vcpu_init_nested() reallocates the array and frees the old buffer while > holding only kvm->arch.config_lock, so a walker can reference the freed > array. It wouldn't hurt to share slightly more information here. Are you dealing with a concurrent MMU notifier? > Allocate the new array outside the lock, as the allocation can sleep, and > do only the copy and the pointer swap under the mmu_lock. After the swap no > walker can reach the old buffer, so free it once the lock has been > released. > > Fixes: 4f128f8e1aaac ("KVM: arm64: nv: Support multiple nested Stage-2 mmu structures") > Signed-off-by: Hyunwoo Kim The diff itself LGTM Reviewed-by: Oliver Upton Thanks, Oliver > --- > arch/arm64/kvm/nested.c | 33 ++++++++++++++++++++------------- > 1 file changed, 20 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > index 38f672e940878..6f7bc9a9992e0 100644 > --- a/arch/arm64/kvm/nested.c > +++ b/arch/arm64/kvm/nested.c > @@ -89,21 +89,28 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu) > * again, and there is no reason to affect the whole VM for this. > */ > num_mmus = atomic_read(&kvm->online_vcpus) * S2_MMU_PER_VCPU; > - tmp = kvrealloc(kvm->arch.nested_mmus, > - size_mul(sizeof(*kvm->arch.nested_mmus), num_mmus), > - GFP_KERNEL_ACCOUNT | __GFP_ZERO); > - if (!tmp) > - return -ENOMEM; > > - swap(kvm->arch.nested_mmus, tmp); > + if (num_mmus > kvm->arch.nested_mmus_size) { > + tmp = kvcalloc(num_mmus, sizeof(*tmp), GFP_KERNEL_ACCOUNT); > + if (!tmp) > + return -ENOMEM; > > - /* > - * If we went through a realocation, adjust the MMU back-pointers in > - * the previously initialised kvm_pgtable structures. > - */ > - if (kvm->arch.nested_mmus != tmp) > - for (int i = 0; i < kvm->arch.nested_mmus_size; i++) > - kvm->arch.nested_mmus[i].pgt->mmu = &kvm->arch.nested_mmus[i]; > + write_lock(&kvm->mmu_lock); > + > + if (kvm->arch.nested_mmus_size) { > + memcpy(tmp, kvm->arch.nested_mmus, > + size_mul(sizeof(*tmp), kvm->arch.nested_mmus_size)); > + > + for (int i = 0; i < kvm->arch.nested_mmus_size; i++) > + tmp[i].pgt->mmu = &tmp[i]; > + } > + > + swap(kvm->arch.nested_mmus, tmp); > + > + write_unlock(&kvm->mmu_lock); > + > + kvfree(tmp); > + } > > for (int i = kvm->arch.nested_mmus_size; !ret && i < num_mmus; i++) > ret = init_nested_s2_mmu(kvm, &kvm->arch.nested_mmus[i]); > -- > 2.43.0 >