From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 4F6373ABD95; Fri, 26 Jun 2026 08:11:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782461503; cv=none; b=hE0IZ84ZgQvh4sFnfmmVT7m9flkU4S4oIyVdi3YD+AW2Ncqh0ofMfEJNTacLyyei0tKs7bP+VI6DCg7L7hZSCoSrOk6Xfq/1bQNECpWZWarv1LQ+cBPH2ajUYhvoKFDuB6G5JCVcC0SvcIvDf66+GeyMv3+unhXbMiZ0ShnYv24= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782461503; c=relaxed/simple; bh=hVK/Pl71amA4YviYJruaHzOlUArxm+8k5y80L8zkszY=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=LESFhrBp9CazSXWj1Vk7Zl80pD8aCJONtJqq+N1q8bIr/Lnqh40JGArhDhCR2/ebV5wg5YITmP7eVG4+rzzN+3k3i4s1/h62u5Vl+HEtEDftcbhbPK2A6Oc49ubw4OJzmmPvSMDAasjnYKy48EWMMt6EQ36wGkpZxqRRZdknyQc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=qgdvJbk8; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="qgdvJbk8" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=jIyhRvMWXkLro+diXzTg4UZFoFs+C0KvlMk7iw2Rp7I=; b=qgdvJbk8oahlFrylNOqVyERALa YGBqg8YIomJYsu8AyWYSxu+Qxk1JyJTicy6bye9gOwyz9dkI1W6I7fHAwnmtVJVg67d1ckzA6odcP iLalXNNhhWNyyY3ZsbLUQ1DOWUjCvI7YwwgMcfWrlJvcqBKLXwPNLGqkDHT0xk+9Vt9XZzxQW3kpD ftKVpr/fAZMR/sEe6yvXMhz0VivsWzOh0mJCWmZiTXsXAv8W8bXdYSmUSlB1XCVjn4Z3lJA3x+C50 kG7daKCdNQGZLy+hfYT7LcT4nvOo85VXvyvRgesHtimDfOBk7QEu5UND8XmomWhsWZoD8/8AGk4Cz 7gnNzLWw==; Received: from [2001:8b0:10b:5:f3d6:3c0c:6c61:8d10] (helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wd1f0-0000000BTfM-1eGD; Fri, 26 Jun 2026 08:11:38 +0000 Message-ID: Subject: Re: [PATCH v3 05/10] KVM: x86/xen: Consolidate checks on Xen vCPU ID for singleshot timer hypercalls From: David Woodhouse To: Sean Christopherson , Vitaly Kuznetsov , Paolo Bonzini , Paul Durrant Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+5b32c49cd8f005e65654@syzkaller.appspotmail.com, syzbot+5d2b94b77112148d1744@syzkaller.appspotmail.com Date: Fri, 26 Jun 2026 09:11:38 +0100 In-Reply-To: <20260625223623.3376478-6-seanjc@google.com> References: <20260625223623.3376478-1-seanjc@google.com> <20260625223623.3376478-6-seanjc@google.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-AaawjVcTCZlo5GvCOYFj" User-Agent: Evolution 3.60.3-0ubuntu1~ppa6 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-AaawjVcTCZlo5GvCOYFj Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2026-06-25 at 15:36 -0700, Sean Christopherson wrote: > Hoist the checks on the Xen vCPU ID when handling set_singleshot_timer an= d > stop_singleshot_timer hypercalls out of their individual case-statements, > so that both checks on the ID are in common code.=C2=A0 kvm_xen_hcall_vcp= u_op() > is already doubly committed to handling only singleshot timer hypercalls, > and even if that were to change in the future, the function could simply > be renamed and turned into a helper specifically for timer hypercalls. >=20 > No functional change intended. Makes sense. In fact these hypercalls are the *only* VCPUOP_xxx calls for which Xen has that restriction (otherwise it would be pointless to have the vcpu argument at all). Which is why we did the check in the individual cases. But these are *also* the only VCPUOP calls we're ever likely to accelerate in the kernel, so that's actually fine. I would prefer to see a comment above the check though. And let's move your patch 4 to come *after* this semantic change. Reviewed-by: David Woodhouse > Signed-off-by: Sean Christopherson > --- > =C2=A0arch/x86/kvm/xen.c | 14 +++++--------- > =C2=A01 file changed, 5 insertions(+), 9 deletions(-) >=20 > diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c > index 27c1aeeab8af..db10f12d10cf 100644 > --- a/arch/x86/kvm/xen.c > +++ b/arch/x86/kvm/xen.c > @@ -1614,13 +1614,13 @@ static bool kvm_xen_hcall_vcpu_op(struct kvm_vcpu= *vcpu, bool longmode, int cmd, > =C2=A0 if (vcpu->arch.xen.vcpu_id =3D=3D XEN_VCPU_ID_INVALID) > =C2=A0 return false; > =C2=A0 /* * Only the set/stop singleshot timer calls are accelerated * by KVM, and they both operate only on the same vCPU. */ > + if (vcpu->arch.xen.vcpu_id !=3D vcpu_id) { > + *r =3D -EINVAL; > + return true; > + } > + > =C2=A0 switch (cmd) { > =C2=A0 case VCPUOP_set_singleshot_timer: > - if (vcpu->arch.xen.vcpu_id !=3D vcpu_id) { > - *r =3D -EINVAL; > - return true; > - } > - > =C2=A0 /* > =C2=A0 * The only difference for 32-bit compat is the 4 bytes of > =C2=A0 * padding after the interesting part of the structure. So > @@ -1648,10 +1648,6 @@ static bool kvm_xen_hcall_vcpu_op(struct kvm_vcpu = *vcpu, bool longmode, int cmd, > =C2=A0 return true; > =C2=A0 > =C2=A0 case VCPUOP_stop_singleshot_timer: > - if (vcpu->arch.xen.vcpu_id !=3D vcpu_id) { > - *r =3D -EINVAL; > - return true; > - } > =C2=A0 kvm_xen_stop_timer(vcpu); > =C2=A0 *r =3D 0; > =C2=A0 return true; --=-AaawjVcTCZlo5GvCOYFj Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj 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