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, URIBL_BLOCKED,USER_AGENT_SANE_1 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 32C0AC5DF62 for ; Wed, 6 Nov 2019 13:02:39 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 8AC61217F4 for ; Wed, 6 Nov 2019 13:02:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8AC61217F4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id C55024A5A0; Wed, 6 Nov 2019 08:02:37 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id zAF9R4YmEI+C; Wed, 6 Nov 2019 08:02:32 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 820614AC7C; Wed, 6 Nov 2019 08:02:32 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id B655A4A5A0 for ; Wed, 6 Nov 2019 08:02:30 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 9vcv2nhSFX8I for ; Wed, 6 Nov 2019 08:02:29 -0500 (EST) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 0AF204A4A0 for ; Wed, 6 Nov 2019 08:02:28 -0500 (EST) 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 758F67A7; Wed, 6 Nov 2019 05:02:27 -0800 (PST) Received: from [10.1.196.63] (e123195-lin.cambridge.arm.com [10.1.196.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D94003F6C4; Wed, 6 Nov 2019 05:02:26 -0800 (PST) Subject: Re: [PATCH v2] KVM: arm64: Don't set HCR_EL2.TVM when S2FWB is supported To: Christoffer Dall , kvmarm@lists.cs.columbia.edu References: <20191028130541.30536-1-christoffer.dall@arm.com> From: Alexandru Elisei Message-ID: <7d3a2fe0-1bf3-0fee-deb6-fa6e0940586a@arm.com> Date: Wed, 6 Nov 2019 13:02:21 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191028130541.30536-1-christoffer.dall@arm.com> Content-Language: en-US Cc: Marc Zyngier , linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Hi, On 10/28/19 1:05 PM, Christoffer Dall wrote: > On CPUs that support S2FWB (Armv8.4+), KVM configures the stage 2 page > tables to override the memory attributes of memory accesses, regardless > of the stage 1 page table configurations, and also when the stage 1 MMU > is turned off. This results in all memory accesses to RAM being > cacheable, including during early boot of the guest. > > On CPUs without this feature, memory accesses were non-cacheable during > boot until the guest turned on the stage 1 MMU, and we had to detect > when the guest turned on the MMU, such that we could invalidate all cache > entries and ensure a consistent view of memory with the MMU turned on. > When the guest turned on the caches, we would call stage2_flush_vm() > from kvm_toggle_cache(). > > However, stage2_flush_vm() walks all the stage 2 tables, and calls > __kvm_flush-dcache_pte, which on a system with S2FWD does ... absolutely > nothing. > > We can avoid that whole song and dance, and simply not set TVM when > creating a VM on a system that has S2FWB. > > Signed-off-by: Christoffer Dall > Reviewed-by: Mark Rutland > --- > I was only able to test this on the model with cache modeling enabled, > but even removing TVM from HCR_EL2 without having FWB also worked with > that setup, so the testing of this has been light. It seems like it > should obviously work, but it would be good if someone with access to > appropriate hardware could give this a spin. > > arch/arm64/include/asm/kvm_arm.h | 3 +-- > arch/arm64/include/asm/kvm_emulate.h | 12 +++++++++++- > 2 files changed, 12 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h > index ddf9d762ac62..6e5d839f42b5 100644 > --- a/arch/arm64/include/asm/kvm_arm.h > +++ b/arch/arm64/include/asm/kvm_arm.h > @@ -61,7 +61,6 @@ > * RW: 64bit by default, can be overridden for 32bit VMs > * TAC: Trap ACTLR > * TSC: Trap SMC > - * TVM: Trap VM ops (until M+C set in SCTLR_EL1) > * TSW: Trap cache operations by set/way > * TWE: Trap WFE > * TWI: Trap WFI > @@ -74,7 +73,7 @@ > * SWIO: Turn set/way invalidates into set/way clean+invalidate > */ > #define HCR_GUEST_FLAGS (HCR_TSC | HCR_TSW | HCR_TWE | HCR_TWI | HCR_VM | \ > - HCR_TVM | HCR_BSU_IS | HCR_FB | HCR_TAC | \ > + HCR_BSU_IS | HCR_FB | HCR_TAC | \ > HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \ > HCR_FMO | HCR_IMO) > #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF) > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h > index d69c1efc63e7..70509799a2a9 100644 > --- a/arch/arm64/include/asm/kvm_emulate.h > +++ b/arch/arm64/include/asm/kvm_emulate.h > @@ -53,8 +53,18 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu) > /* trap error record accesses */ > vcpu->arch.hcr_el2 |= HCR_TERR; > } > - if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) > + > + if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) { > vcpu->arch.hcr_el2 |= HCR_FWB; > + } else { > + /* > + * For non-FWB CPUs, we trap VM ops (HCR_EL2.TVM) until M+C > + * get set in SCTLR_EL1 such that we can detect when the guest > + * MMU gets turned off and do the necessary cache maintenance > + * then. > + */ > + vcpu->arch.hcr_el2 &= ~HCR_TVM; > + } > > if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) > vcpu->arch.hcr_el2 &= ~HCR_RW; This patch makes sense to me: when FWB is available, the guest memory is cacheable even when the stage 1 MMU is disabled, which means it's now impossible to have a situation where the data in memory is newer than the data in the cache. I tested the patch with the fix suggested by Marc by doing a linux boot and then a 'ls -R /', and by running kvm-unit-tests in a loop a couple dozen times. For what it's worth: Tested-by: Alexandru Elisei I do need to point out that I haven't been able to make a guest misbehave when FWB is not enabled *and* KVM doesn't do a stage2_flush_vm when the stage 1 MMU is enabled. I tried to write two different tests in kvm-unit-tests: 1. With the MMU never enabled, the test tells the host to read a value from memory (so a cache line is allocated), writes another value to the same memory location, and then enables the MMU and reads the memory back. I always got the latest value that was written while the MMU was off. 2. One thread tells the host to read the memory location in a loop (to make sure that the cache line doesn't get evicted), while the other thread writes a value with the MMU off, enables the MMU and reads the memory back. I still got the latest value written with the MMU off. I can share the source code for the tests, if anyone is interested; I'm also open to other suggestions. Regards, Alex _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm