From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AA9CFC2D0DB for ; Thu, 30 Jan 2020 14:15:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A6CC2083E for ; Thu, 30 Jan 2020 14:15:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580393705; bh=fLFS4MsI4Xqb1q1b9ZZYwHXmgmXnIzhWE8jaSJpBJnw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=niYhEHlPPoHogsg3FyFAkOfUPUSDtJcx+kRCjDN1jZvgQsawZR94FYdoPvAU9szeB TDDyb7oC6c0TH5VaPaWAm5YfOQe35gXNIxXtOQTRRMMQLgduUnv4qTpszUz1VP+dQh QNDCjSueHFesK5ZvuWw+56z1aFDds/eyp0amX54Y= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727228AbgA3OPE (ORCPT ); Thu, 30 Jan 2020 09:15:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:32938 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726902AbgA3OPE (ORCPT ); Thu, 30 Jan 2020 09:15:04 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 53C3420658; Thu, 30 Jan 2020 14:15:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580393703; bh=fLFS4MsI4Xqb1q1b9ZZYwHXmgmXnIzhWE8jaSJpBJnw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=zawswnw40D17Q1KUd03C6hPxIndcJI5s2TZeJo6VFYYy5ucA3alcao9/hf6EqGLYR PjJsxO5AE8c/e8qs94nzYRBolHmEkXUlAEotO/IWphwKKXx6bKdk6HpLEWoTBezxnH yQesQwLUpAVuVw5/aKKSdzdx/IoP/veeZ1lFuBy8= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1ixAaz-002CVK-JM; Thu, 30 Jan 2020 14:15:01 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 30 Jan 2020 14:15:01 +0000 From: Marc Zyngier To: Alexandru Elisei Cc: Paolo Bonzini , Andrew Jones , Andrew Murray , Beata Michalska , Christoffer Dall , Eric Auger , Gavin Shan , Haibin Wang , James Morse , Mark Brown , Mark Rutland , Russell King , Shannon Zhao , Steven Price , Will Deacon , YueHaibing , Zenghui Yu , Julien Thierry , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org Subject: Re: [PATCH 23/23] KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer In-Reply-To: References: <20200130132558.10201-1-maz@kernel.org> <20200130132558.10201-24-maz@kernel.org> Message-ID: <6898d36c8453756418924bf4718219fd@kernel.org> X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.8 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: alexandru.elisei@arm.com, pbonzini@redhat.com, drjones@redhat.com, andrew.murray@arm.com, beata.michalska@linaro.org, christoffer.dall@arm.com, eric.auger@redhat.com, gshan@redhat.com, wanghaibin.wang@huawei.com, james.morse@arm.com, broonie@kernel.org, mark.rutland@arm.com, rmk+kernel@armlinux.org.uk, shannon.zhao@linux.alibaba.com, steven.price@arm.com, will@kernel.org, yuehaibing@huawei.com, yuzenghui@huawei.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2020-01-30 14:11, Alexandru Elisei wrote: > Hi, > > On 1/30/20 1:25 PM, Marc Zyngier wrote: >> From: Alexandru Elisei >> >> According to the ARM ARM, registers CNT{P,V}_TVAL_EL0 have bits >> [63:32] >> RES0 [1]. When reading the register, the value is truncated to the >> least >> significant 32 bits [2], and on writes, TimerValue is treated as a >> signed >> 32-bit integer [1, 2]. >> >> When the guest behaves correctly and writes 32-bit values, treating >> TVAL >> as an unsigned 64 bit register works as expected. However, things >> start >> to break down when the guest writes larger values, because >> (u64)0x1_ffff_ffff = 8589934591. but (s32)0x1_ffff_ffff = -1, and the >> former will cause the timer interrupt to be asserted in the future, >> but >> the latter will cause it to be asserted now. Let's treat TVAL as a >> signed 32-bit register on writes, to match the behaviour described in >> the architecture, and the behaviour experimentally exhibited by the >> virtual timer on a non-vhe host. >> >> [1] Arm DDI 0487E.a, section D13.8.18 >> [2] Arm DDI 0487E.a, section D11.2.4 >> >> Signed-off-by: Alexandru Elisei >> [maz: replaced the read-side mask with lower_32_bits] >> Signed-off-by: Marc Zyngier >> Fixes: 8fa761624871 ("KVM: arm/arm64: arch_timer: Fix CNTP_TVAL >> calculation") >> Link: >> https://lore.kernel.org/r/20200127103652.2326-1-alexandru.elisei@arm.com >> --- >> virt/kvm/arm/arch_timer.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c >> index f182b2380345..c6c2a9dde00c 100644 >> --- a/virt/kvm/arm/arch_timer.c >> +++ b/virt/kvm/arm/arch_timer.c >> @@ -805,6 +805,7 @@ static u64 kvm_arm_timer_read(struct kvm_vcpu >> *vcpu, >> switch (treg) { >> case TIMER_REG_TVAL: >> val = timer->cnt_cval - kvm_phys_timer_read() + timer->cntvoff; >> + val &= lower_32_bits(val); > > This is correct, but how about making it val = lower_32_bits(val) for > more > clarity? Apologies for not spotting it earlier :( That's what it should have been, but I obviously typoed it. As it passed all my tests, I didn't notice the issue. I'll queue a cleanup once Paolo has a chance to pull this. M. -- Jazz is not dead. It just smells funny...