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 45B0F1C5D72; Sat, 27 Jun 2026 14:03:19 +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=1782569001; cv=none; b=q+lUIXK7sBa4KYFPa77o5sHc72tSUEzQIy5vuhZbrapCcmcPDk5uCqWY/oJxYHZ17+DicLgTEzGTp4z0OEz+5g5uOxHg99shgMU4CW3c+IS+BKJP3tYFg/cO8mKLAF2xFMFmwRAyjwFnadYph9W9sC5mSIrFA9BLZTPN6bRrGR8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782569001; c=relaxed/simple; bh=qND3wML3Eq1/a3k5SVv1WetF2hiIeZqkU9WQV+uPOwk=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=JW2r2hgPiHOMFIOGnrQWrrCMwqyDiNJHBA+ztNLOjdxprRLZ23ub7HsSl+O2Jm/xYAaYqLi7q02snoS1xcRbfPFa4Rsiexldvu+69rQvRns/lGRSERYzB39SbLiLsv523ZJlaToXu4mwnMpJDfzaeoP8Iw5WibTJ9AJik+ZiB8A= 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=nF9mEDrI; 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="nF9mEDrI" 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=qND3wML3Eq1/a3k5SVv1WetF2hiIeZqkU9WQV+uPOwk=; b=nF9mEDrI4AYBwD9VDohLUKjwlz OCmaNAGmG2Qd12jGmkQXzcXQwmZxymT4xY+w4o2i6ozLM5k0YOkiAGXhT/urXhCbkUimrLTspJQn2 UeUKIsaOl/34RVIa+2WdYLYJPik3yoD5YFhM/zWGAbPp8g7wLgGwOz8BEcvEuiMc3Yc+F27XaHqQs cGZcePSxpYpXWzZFyK7ybELY1b9ZHhtBOeRrkUG8/TScSByLiTRbY2t0p6JFXBbHigwKxvp+FZNyP D0IDs8+TV86cZBxpjiRi7h72EkgNjNXdIwR4Z6p0l+jjRUYLuhkQagtaX1oBibLlLG0xZrrbQ883L B1Zvw4zQ==; Received: from [2001:8b0:10b:5:2974:86dd:e981:2b24] (helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wdTcq-00000000ORA-3o2t; Sat, 27 Jun 2026 14:03:17 +0000 Message-ID: <26102f5f734a050db73a74755e7d7d06eee28afd.camel@infradead.org> 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 Cc: Vitaly Kuznetsov , Paolo Bonzini , Paul Durrant , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+5b32c49cd8f005e65654@syzkaller.appspotmail.com, syzbot+5d2b94b77112148d1744@syzkaller.appspotmail.com Date: Sat, 27 Jun 2026 15:03:16 +0100 In-Reply-To: References: <20260625223623.3376478-1-seanjc@google.com> <20260625223623.3376478-6-seanjc@google.com> <5838fbf9c799d135b06ba61b7879a231e314f7b5.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-pDKcdomXICmedgDx/aFG" 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 --=-pDKcdomXICmedgDx/aFG Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2026-06-26 at 11:12 -0700, Sean Christopherson wrote: >=20 > I disagree.=C2=A0 The old code uses a common check for kvm_xen_timer_enab= led(), which > is confusing and actively dangerous, as evidenced by my goof, because it'= s easy > to miss that the only reason KVM can bail early for !kvm_xen_timer_enable= d() is > because it returns false.=C2=A0 Punting hypercalls that are never acceler= ated by KVM > because some other hypercall happens to be disabled is nasty. Fair enough. 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