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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 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 03E06C32771 for ; Mon, 6 Jan 2020 11:17:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C94D9207FD for ; Mon, 6 Jan 2020 11:17:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726281AbgAFLRW (ORCPT ); Mon, 6 Jan 2020 06:17:22 -0500 Received: from foss.arm.com ([217.140.110.172]:43026 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726155AbgAFLRV (ORCPT ); Mon, 6 Jan 2020 06:17:21 -0500 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 D08F6328; Mon, 6 Jan 2020 03:17:20 -0800 (PST) Received: from donnerap.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CF54E3F534; Mon, 6 Jan 2020 03:17:19 -0800 (PST) Date: Mon, 6 Jan 2020 11:17:16 +0000 From: Andre Przywara To: Alexandru Elisei Cc: mark.rutland@arm.com, kvm@vger.kernel.org, pbonzini@redhat.com, drjones@redhat.com, maz@kernel.org, vladimir.murzin@arm.com Subject: Re: [kvm-unit-tests PATCH v3 06/18] arm/arm64: psci: Don't run C code without stack or vectors Message-ID: <20200106111716.692c949f@donnerap.cambridge.arm.com> In-Reply-To: <61ea7391-7e65-4548-17b6-7dbd977fa394@arm.com> References: <1577808589-31892-1-git-send-email-alexandru.elisei@arm.com> <1577808589-31892-7-git-send-email-alexandru.elisei@arm.com> <20200102181121.6895344d@donnerap.cambridge.arm.com> <61ea7391-7e65-4548-17b6-7dbd977fa394@arm.com> Organization: ARM X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; aarch64-unknown-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, 6 Jan 2020 10:41:55 +0000 Alexandru Elisei wrote: > Hi Andre, > > Thank you for reviewing the patches! > > On 1/2/20 6:11 PM, Andre Przywara wrote: > > On Tue, 31 Dec 2019 16:09:37 +0000 > > Alexandru Elisei wrote: > > > > Hi, > > > >> The psci test performs a series of CPU_ON/CPU_OFF cycles for CPU 1. This is > >> done by setting the entry point for the CPU_ON call to the physical address > >> of the C function cpu_psci_cpu_die. > >> > >> The compiler is well within its rights to use the stack when generating > >> code for cpu_psci_cpu_die. > > I am a bit puzzled: Is this an actual test failure at the moment? Or just a potential problem? Because I see it using the stack pointer in the generated code in lib/arm/psci.o. But the psci test seems to pass. Or is that just because the SP is somehow not cleared, because of some KVM implementation specifics? > > The test checks for the return value of the CPU_ON function. What the CPU does > while it's live is inconsequential. OK, I see. > > One more thing below ... > > > >> However, because no stack initialization has > >> been done, the stack pointer is zero, as set by KVM when creating the VCPU. > >> This causes a data abort without a change in exception level. The VBAR_EL1 > >> register is also zero (the KVM reset value for VBAR_EL1), the MMU is off, > >> and we end up trying to fetch instructions from address 0x200. > >> > >> At this point, a stage 2 instruction abort is generated which is taken to > >> KVM. KVM interprets this as an instruction fetch from an I/O region, and > >> injects a prefetch abort into the guest. Prefetch abort is a synchronous > >> exception, and on guest return the VCPU PC will be set to VBAR_EL1 + 0x200, > >> which is... 0x200. The VCPU ends up in an infinite loop causing a prefetch > >> abort while fetching the instruction to service the said abort. > >> > >> cpu_psci_cpu_die is basically a wrapper over the HVC instruction, so > >> provide an assembly implementation for the function which will serve as the > >> entry point for CPU_ON. > >> > >> Signed-off-by: Alexandru Elisei > >> --- > >> arm/cstart.S | 7 +++++++ > >> arm/cstart64.S | 7 +++++++ > >> arm/psci.c | 5 +++-- > >> 3 files changed, 17 insertions(+), 2 deletions(-) > >> > >> diff --git a/arm/cstart.S b/arm/cstart.S > >> index 2c81d39a666b..dfef48e4dbb2 100644 > >> --- a/arm/cstart.S > >> +++ b/arm/cstart.S > >> @@ -7,6 +7,7 @@ > >> */ > >> #define __ASSEMBLY__ > >> #include > >> +#include > >> #include > >> #include > >> #include > >> @@ -139,6 +140,12 @@ secondary_entry: > >> blx r0 > >> b do_idle > >> > >> +.global asm_cpu_psci_cpu_die > >> +asm_cpu_psci_cpu_die: > >> + ldr r0, =PSCI_0_2_FN_CPU_OFF > >> + hvc #0 > >> + b . > > I am wondering if this implementation is actually too simple. Both the current implementation and the kernel clear at least the first three arguments to 0. > > I failed to find a requirement for doing this (nothing in the SMCCC or the PSCI spec), but I guess it would make sense when looking at forward compatibility. > > The SMC calling convention only specifies the values for the arguments that are > used by a function, not the values for all possible arguments. kvm-unit-tests sets > the other arguments to 0 because the function prototype that does the actual SMC > call takes 4 arguments. The value 0 is a random value that was chosen for those > unused parameters. For example, it could have been a random number on each call. > > Let me put it another way. Suggesting that unused arguments should be set to 0 is > the same as suggesting that normal C function that adheres to procedure call > standard for arm64 should always have 8 arguments, and for a particular function > that doesn't use all of them, they should be set to 0 by the caller. I understand that, but was wondering if the SMCCC would mandate stricter requirements. After all every PSCI call from Linux goes through a function which clears all unused input parameters. Cheers, Andre. > @Mark Rutland has worked on the SMC implementation for the Linux kernel, if he > wants to chime in on this. > > Thanks, > Alex > > At the very least it's a change in behaviour (ignoring the missing printf). > > So shall we just clear r1, r2 and r3 here? (Same for arm64 below) > > > > Cheers, > > Andre > > > >> + > >> .globl halt > >> halt: > >> 1: wfi > >> diff --git a/arm/cstart64.S b/arm/cstart64.S > >> index b0e8baa1a23a..c98842f11e90 100644 > >> --- a/arm/cstart64.S > >> +++ b/arm/cstart64.S > >> @@ -7,6 +7,7 @@ > >> */ > >> #define __ASSEMBLY__ > >> #include > >> +#include > >> #include > >> #include > >> #include > >> @@ -128,6 +129,12 @@ secondary_entry: > >> blr x0 > >> b do_idle > >> > >> +.globl asm_cpu_psci_cpu_die > >> +asm_cpu_psci_cpu_die: > >> + ldr x0, =PSCI_0_2_FN_CPU_OFF > >> + hvc #0 > >> + b . > >> + > >> .globl halt > >> halt: > >> 1: wfi > >> diff --git a/arm/psci.c b/arm/psci.c > >> index 5c1accb6cea4..c45a39c7d6e8 100644 > >> --- a/arm/psci.c > >> +++ b/arm/psci.c > >> @@ -72,6 +72,7 @@ static int cpu_on_ret[NR_CPUS]; > >> static cpumask_t cpu_on_ready, cpu_on_done; > >> static volatile int cpu_on_start; > >> > >> +extern void asm_cpu_psci_cpu_die(void); > >> static void cpu_on_secondary_entry(void) > >> { > >> int cpu = smp_processor_id(); > >> @@ -79,7 +80,7 @@ static void cpu_on_secondary_entry(void) > >> cpumask_set_cpu(cpu, &cpu_on_ready); > >> while (!cpu_on_start) > >> cpu_relax(); > >> - cpu_on_ret[cpu] = psci_cpu_on(cpus[1], __pa(cpu_psci_cpu_die)); > >> + cpu_on_ret[cpu] = psci_cpu_on(cpus[1], __pa(asm_cpu_psci_cpu_die)); > >> cpumask_set_cpu(cpu, &cpu_on_done); > >> } > >> > >> @@ -104,7 +105,7 @@ static bool psci_cpu_on_test(void) > >> cpu_on_start = 1; > >> smp_mb(); > >> > >> - cpu_on_ret[0] = psci_cpu_on(cpus[1], __pa(cpu_psci_cpu_die)); > >> + cpu_on_ret[0] = psci_cpu_on(cpus[1], __pa(asm_cpu_psci_cpu_die)); > >> cpumask_set_cpu(0, &cpu_on_done); > >> > >> while (!cpumask_full(&cpu_on_done))