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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 2C6EFC388F9 for ; Wed, 21 Oct 2020 13:37:41 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7F9E0208C3 for ; Wed, 21 Oct 2020 13:37:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="jAts8p1A" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7F9E0208C3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=1wvp34HKWM/UGSQ4xN0oMiuDbgL4fhNpu/ayoRHe1mk=; b=jAts8p1APt6yx96wsx6E4oO3Y kQrFir8H3PtvV22Pwp92VP/YV+ouhBjWQmY6RJGUHbsIFnwFaoRFaohHm2ysQJAvqyIJE9+ds/Lq5 m3LPiItEZSIvTE9sFZkvS85mUb1G7hUNRyKQfCrMfM0/KP4PEDIe9L471rCWx0W3sWT+nwz/ZGiTI DRz4tRuCA5S9xRnz/73mmQi7JGU+glAmofHE2EgWxkQpUH1M/2SzG0kHVpyKtsqsTiklI7fMZBygI uIMyGA/ND+C47feIwZAVjb1oZVPmiZ2AbcXb2rwbrGy0sX1tcPJgLtWi/mnf94dOsWFn82aGPAUqd WtiIgSxxw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kVEHQ-0007mO-UV; Wed, 21 Oct 2020 13:35:53 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kVEHM-0007li-VO for linux-arm-kernel@lists.infradead.org; Wed, 21 Oct 2020 13:35:50 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A78B831B; Wed, 21 Oct 2020 06:35:47 -0700 (PDT) Received: from e107158-lin (e107158-lin.cambridge.arm.com [10.1.194.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5371B3F66B; Wed, 21 Oct 2020 06:35:46 -0700 (PDT) Date: Wed, 21 Oct 2020 14:35:43 +0100 From: Qais Yousef To: Marc Zyngier Subject: Re: [RFC PATCH v2 1/4] arm64: kvm: Handle Asymmetric AArch32 systems Message-ID: <20201021133543.zeyghjzujivnds2d@e107158-lin> References: <20201021104611.2744565-1-qais.yousef@arm.com> <20201021104611.2744565-2-qais.yousef@arm.com> <4035e634eb2bfce4b88a159b2ec2f267@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4035e634eb2bfce4b88a159b2ec2f267@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201021_093549_118139_80F09434 X-CRM114-Status: GOOD ( 36.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Will Deacon , "Peter Zijlstra \(Intel\)" , Catalin Marinas , James Morse , Greg Kroah-Hartman , Linus Torvalds , Morten Rasmussen , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 10/21/20 13:02, Marc Zyngier wrote: > On 2020-10-21 11:46, Qais Yousef wrote: > > On a system without uniform support for AArch32 at EL0, it is possible > > for the guest to force run AArch32 at EL0 and potentially cause an > > illegal exception if running on the wrong core. > > s/the wrong core/a core without AArch32/ > > > > > Add an extra check to catch if the guest ever does that and prevent it > > Not "if the guest ever does that". Rather "let's hope we are lucky enough > to catch the guest doing that". > > > from running again by resetting vcpu->arch.target and return > > ARM_EXCEPTION_IL. > > > > We try to catch this misbehavior as early as possible and not rely on > > PSTATE.IL to occur. > > > > Tested on Juno by instrumenting the host to: > > > > * Fake asym aarch32. > > * Instrument KVM to make the asymmetry visible to the guest. > > > > Any attempt to run 32bit app in the guest will produce such error on > > qemu: > > Not *any* attempt. Only the ones where the guest exits whilst in > AArch32 EL0. It is perfectly possible for the guest to use AArch32 > undetected for quite a while. Thanks Marc! I'll change them all. > > > > # ./test > > error: kvm run failed Invalid argument > > PC=ffff800010945080 X00=ffff800016a45014 X01=ffff800010945058 > > X02=ffff800016917190 X03=0000000000000000 X04=0000000000000000 > > X05=00000000fffffffb X06=0000000000000000 X07=ffff80001000bab0 > > X08=0000000000000000 X09=0000000092ec5193 X10=0000000000000000 > > X11=ffff80001608ff40 X12=ffff000075fcde86 X13=ffff000075fcde88 > > X14=ffffffffffffffff X15=ffff00007b2105a8 X16=ffff00007b006d50 > > X17=0000000000000000 X18=0000000000000000 X19=ffff00007a82b000 > > X20=0000000000000000 X21=ffff800015ccd158 X22=ffff00007a82b040 > > X23=ffff00007a82b008 X24=0000000000000000 X25=ffff800015d169b0 > > X26=ffff8000126d05bc X27=0000000000000000 X28=0000000000000000 > > X29=ffff80001000ba90 X30=ffff80001093f3dc SP=ffff80001000ba90 > > PSTATE=60000005 -ZC- EL1h > > qemu-system-aarch64: Failed to get KVM_REG_ARM_TIMER_CNT > > It'd be worth working out: > - why does this show an AArch64 mode it we caught the vcpu in AArch32? > - why does QEMU shout about the timer register? /me puts a monocular on Which bit is the AArch64? It did surprise me that it is shouting about the timer. My guess was that a timer interrupt at the guest between exit/reentry caused the state change and the failure to read the timer register? Since the target is no longer valid it falls over, hopefully as expected. I could have been naive of course. That explanation made sense to my mind so I didn't dig further. > > Aborted > > > > Signed-off-by: Qais Yousef > > --- > > arch/arm64/kvm/arm.c | 13 +++++++++++++ > > 1 file changed, 13 insertions(+) > > > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > index b588c3b5c2f0..c2fa57f56a94 100644 > > --- a/arch/arm64/kvm/arm.c > > +++ b/arch/arm64/kvm/arm.c > > @@ -804,6 +804,19 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) > > > > preempt_enable(); > > > > + /* > > + * The ARMv8 architecture doesn't give the hypervisor > > + * a mechanism to prevent a guest from dropping to AArch32 EL0 > > + * if implemented by the CPU. If we spot the guest in such > > + * state and that we decided it wasn't supposed to do so (like > > + * with the asymmetric AArch32 case), return to userspace with > > + * a fatal error. > > + */ > > Please add a comment explaining the effects of setting target to -1. > Something > like: > > "As we have caught the guest red-handed, decide that it isn't fit for > purpose > anymore by making the4 vcpu invalid. The VMM can try and fix it by issuing > a KVM_ARM_VCPU_INIT if it really wants to." Will do. Thanks -- Qais Yousef > > > + if (!system_supports_32bit_el0() && vcpu_mode_is_32bit(vcpu)) { > > + vcpu->arch.target = -1; > > + ret = ARM_EXCEPTION_IL; > > + } > > + > > ret = handle_exit(vcpu, ret); > > } > > M. > -- > Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel