From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f202.google.com (mail-pf1-f202.google.com [209.85.210.202]) (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 7BF3A1ABEA7 for ; Fri, 2 Aug 2024 20:51:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722631893; cv=none; b=WYQFYyXSvSqcHMemhGgHzcrti+cYm+jm+xIWcmmnfX/55jTkW+EuMreD8gkSPKdKRUnsMkrmb1eiy5ggvgZYtiaIRlm9gA8uFSGjFi91I8AHF8/ewaWOcSuhy7MvFOnLTUlgijO0PGDmVIjLOYwuKO/Uh2MP5CTxV2oWmKTpPnM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722631893; c=relaxed/simple; bh=FueBNgDDCfYI2k+0y4y+ZR1Vsa5mvu9gB1exHHHan94=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=m5ZBIVpKmaTP3MKE3BfXi2ULkJl3xRVjMyGg9nZGSwzrzhxtxRGMphkOUa/kjF/v8i4WVqIZsz0e35c4BoNwCLySLBNo+h07V1NMsR+NQFdi09GbAoG0IqBluXt0GcyVJGrzFv7fa9I2PKONxZtUs3jvKZw6AMES93jyI4wcgHA= 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=dG87xNtM; arc=none smtp.client-ip=209.85.210.202 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="dG87xNtM" Received: by mail-pf1-f202.google.com with SMTP id d2e1a72fcca58-70e9ea89b42so7816550b3a.3 for ; Fri, 02 Aug 2024 13:51:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1722631892; x=1723236692; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=tXkYm8GWgU7Uugm4gxQOf+EOoFr0lG6UD/VJhjiOPnM=; b=dG87xNtM3VLx+c+QMuryFY30aJ15tBOPtpwpo4+bhEVpRyCtFI1Jv1f0bzykPJgg/I NIPJN320Ukuzi9yfoo9cihjcJRcQmFRax0ffjpd0PTfRmz08j0xo1l7F3bWExgqL6NrI l28oPFyBQKv8CeYtx1yyJn1wxwc8ow8LwVmmRiDGT/lL7iY4VwuhwOpY2HRSsLIIpJrY OkrMb6rKV7xqVed8I9BzWwzsELuG/R0Yxk8fAzdRLrwRzjFzqAZJ9FBCj0D6EtrqX98E bn82vqF9DFHewXlIWHPceyCzIUu1r0/Pzyo+qcmlsUuT8aII1R/nHX3kmVTWXT7q2R21 H9kA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1722631892; x=1723236692; h=content-transfer-encoding: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=tXkYm8GWgU7Uugm4gxQOf+EOoFr0lG6UD/VJhjiOPnM=; b=WZKEE/K2/B2a8tf5r2P8C26exCy+6sGdZu+b2BSuhiskvWUegPEkIgqrFLsesfqked DFRlF0+VeT4j8+V1jSIJzpqLZ3wr7tyhBkLxu9mr0EKEZOAqfWOUnrlOuG2LVldfUItI GeJ+vfIy4FiKNRjz4QINdflLUqYTv0xlXGnEZSSs//vvjbUWTrKh1egzijfQPTd1w7pr H0DwuJjh0XRhJic4Oerj7FwhN2bDuFxh0T+qZ2Aw44/U4DX7sAJx2AkjlN0BhqIF1rAK Rmf+dJ28G61RcIBgl1kSdhdb4e/aBIrKTAhahMRcQ/LJYK4jE5ZBCD8YPoufwENlBfXp v9bQ== X-Forwarded-Encrypted: i=1; AJvYcCVrK2vyvex2ipRxBzzFrbHDRRr5JNrnbojpQs9sMJPBxv/VtxvWTEoG06idT7cobJFy1UXTCq+wX+xT5NVIDYELDCzBOXsnIRzrkXkq X-Gm-Message-State: AOJu0YwVo5x1HmuAJvel0DlekONYM7qvSMOS+sA52tt2Cy0kru+ZKhsi COdWE9P20D9OFvEpbRA33p+t0V7xTlauBP5At1bpwjA/vL69J0cxV0ZXRR9Gtg4kiYozFECmnVq NWA== X-Google-Smtp-Source: AGHT+IE1tZi1nsiH0SIgqwEaG7Vb1R0ZlJXHcVhuB6HgEl7rj1NR5a6/czPeOlKS3H+iSO3nwk8SFUENvrM= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:6a00:6f01:b0:70d:fba:c51c with SMTP id d2e1a72fcca58-7106d071bd2mr16631b3a.3.1722631891698; Fri, 02 Aug 2024 13:51:31 -0700 (PDT) Date: Fri, 2 Aug 2024 13:51:30 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240802200136.329973-1-seanjc@google.com> <20240802200136.329973-3-seanjc@google.com> Message-ID: Subject: Re: [PATCH 2/2] KVM: Protect vCPU's "last run PID" with rwlock, not RCU From: Sean Christopherson To: Steve Rutherford Cc: Marc Zyngier , Oliver Upton , Paolo Bonzini , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Fri, Aug 02, 2024, Steve Rutherford wrote: > On Fri, Aug 2, 2024 at 1:01=E2=80=AFPM Sean Christopherson wrote: > > @@ -4178,9 +4181,9 @@ static int vcpu_get_pid(void *data, u64 *val) > > { > > struct kvm_vcpu *vcpu =3D data; > > > > - rcu_read_lock(); > > - *val =3D pid_nr(rcu_dereference(vcpu->pid)); > > - rcu_read_unlock(); > > + read_lock(&vcpu->pid_lock); > > + *val =3D pid_nr(vcpu->pid); > > + read_unlock(&vcpu->pid_lock); > > return 0; > > } > > > > @@ -4466,7 +4469,7 @@ static long kvm_vcpu_ioctl(struct file *filp, > > r =3D -EINVAL; > > if (arg) > > goto out; > > - oldpid =3D rcu_access_pointer(vcpu->pid); > > + oldpid =3D vcpu->pid; >=20 > Overall this patch looks correct, but this spot took me a moment, and > I want to confirm. This skips the reader lock since writing only > happens just below, under the vcpu lock, and we've already taken that > lock? Yep, exactly.