From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-102.mta0.migadu.com [91.218.175.102]) (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 9851C43E07D for ; Fri, 14 Aug 2026 09:28:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.102 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786699717; cv=none; b=Hm1YeIDi7Dk68XzPC7YMM0VbAavlLzqsQBv/s6Fob+nqhPwAzZN5RV30enS0in7Hkn1dvd9NoYzBNxMKLcLhuxiNrs6PeZElkEGyLqqkMaPIE+X+Q7x19tdc11H8YEOLjYCNTBggOm/6+ZupKt9P3YFspkvbFklJ5nl4Y0dxym8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786699717; c=relaxed/simple; bh=aKc6Ht70FpFYHMi3v//T6si9m2aQw7blmfmTGQZxG04=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=Esdvy4XpKDNfOkpUXYdtWMY55ny1jNV5o0dgLjYRLDevN34DDOk3HsO1yNXMkUYkKU2VhMfUtq/opiqgtKDklf9clmF0hlIkUt+xQHRtp/h1CKUjeDzqM7t0/CoQfxeIbYsuMOdzK34e5nFSwAyEoz/tW6UBZjaqb3CqleeSs5s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Ks8oAYzH; arc=none smtp.client-ip=91.218.175.102 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Ks8oAYzH" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=aKc6Ht70FpFYHMi3v//T6si9m2aQw7blmfmTGQZxG04=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1786699712; v=1; x=1787304512; b=Ks8oAYzHnx5RvCsRWtQbvI4hceWIX8H70sr8vqSld9LYxWM5+Fy00pEGrqgfDf5KR9z2q/1r +Fh/dVqO9jlB4P3k4YSTLJv/8vBzRv+nl4CdWfVaiYs0aqM9Y/UuLfGkGyRDK6DNRVMpVR4qsC8 tzaAYgMtqkVNWemQG3FRmzZs= X-Envelope-To: linux-kernel@vger.kernel.org Received: from [192.168.1.116] (111.162.215.50) by smtp.migadu.com with ESMTPS id 3cf49401cfb7d1c4; Fri, 14 Aug 2026 09:28:32 +0000 X-Migadu-Flow: FLOW_OUT Message-ID: <5e5f26fb-8c8f-4326-bf47-ef25dbd62c01@linux.dev> Date: Fri, 14 Aug 2026 17:28:25 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: cui.tao@linux.dev, zhaotianrui@loongson.cn, kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, Tao Cui Subject: Re: [PATCH v2] LoongArch: KVM: Fix TOCTOU race on pv_features To: Huacai Chen , Bibo Mao References: <20260813232542.2098930-1-cui.tao@linux.dev> From: Tao Cui In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Huacai, 在 2026/8/14 16:24, Huacai Chen 写道: > Hi, Tao, > > On Fri, Aug 14, 2026 at 9:09 AM Bibo Mao wrote: >> >> >> >> On 2026/8/14 上午7:25, Tao Cui wrote: >>> From: Tao Cui >>> >>> The check-then-set on kvm->arch.pv_features in >>> kvm_loongarch_cpucfg_set_attr() is lockless, so two vCPUs can race >>> past the validation and set different values. Add a spinlock to >>> serialize it. >>> >>> Signed-off-by: Tao Cui >>> --- >>> >>> Changes in v2: use a spinlock instead of a cmpxchg loop (Bibo Mao). >>> Link: https://lore.kernel.org/all/20260810081321.157258-1-cui.tao@linux.dev/ >>> >>> arch/loongarch/include/asm/kvm_host.h | 2 ++ >>> arch/loongarch/kvm/vcpu.c | 6 +++++- >>> arch/loongarch/kvm/vm.c | 1 + >>> 3 files changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h >>> index 23cfbecebbd7..cdbbd90e0584 100644 >>> --- a/arch/loongarch/include/asm/kvm_host.h >>> +++ b/arch/loongarch/include/asm/kvm_host.h >>> @@ -128,6 +128,8 @@ struct kvm_arch { >>> struct kvm_phyid_map *phyid_map; >>> /* Enabled PV features */ >>> unsigned long pv_features; >>> + /* Serializes pv_features updates */ >>> + spinlock_t pv_features_lock; > I think it is better to rename it to pv_setting_lock, and put it near > phyid_map_lock. > Got it, v3 on the way with the rename and the lock moved. Thanks, Tao > Huacai > >>> /* Supported KVM features */ >>> unsigned long kvm_features; >>> >>> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c >>> index 20c207d80e31..551ed39b2d1f 100644 >>> --- a/arch/loongarch/kvm/vcpu.c >>> +++ b/arch/loongarch/kvm/vcpu.c >>> @@ -1165,10 +1165,14 @@ static int kvm_loongarch_cpucfg_set_attr(struct kvm_vcpu *vcpu, >>> return -EINVAL; >>> >>> /* All vCPUs need set the same PV features */ >>> + spin_lock(&kvm->arch.pv_features_lock); >>> if ((kvm->arch.pv_features & LOONGARCH_PV_FEAT_UPDATED) >>> - && ((kvm->arch.pv_features & valid) != val)) >>> + && ((kvm->arch.pv_features & valid) != val)) { >>> + spin_unlock(&kvm->arch.pv_features_lock); >>> return -EINVAL; >>> + } >>> kvm->arch.pv_features = val | LOONGARCH_PV_FEAT_UPDATED; >>> + spin_unlock(&kvm->arch.pv_features_lock); >>> return 0; >>> default: >>> return -ENXIO; >>> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c >>> index 1317c718f896..b984cc54f305 100644 >>> --- a/arch/loongarch/kvm/vm.c >>> +++ b/arch/loongarch/kvm/vm.c >>> @@ -76,6 +76,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type) >>> return -ENOMEM; >>> } >>> spin_lock_init(&kvm->arch.phyid_map_lock); >>> + spin_lock_init(&kvm->arch.pv_features_lock); >>> >>> kvm_init_vmcs(kvm); >>> kvm_vm_init_features(kvm); >>> >> Reviewed-by: Bibo Mao >>