From patchwork Wed Sep 20 08:01:33 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oliver Upton X-Patchwork-Id: 13392251 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F1CCBCE79AC for ; Wed, 20 Sep 2023 08:01:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232960AbjITIB7 (ORCPT ); Wed, 20 Sep 2023 04:01:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232708AbjITIB6 (ORCPT ); Wed, 20 Sep 2023 04:01:58 -0400 Received: from out-227.mta1.migadu.com (out-227.mta1.migadu.com [95.215.58.227]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14AFE97 for ; Wed, 20 Sep 2023 01:01:53 -0700 (PDT) X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1695196911; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=uvviR8Tdi7KfiLkhBYZ0V8IZJiQLCIG8mWutZwpfO4Y=; b=Q1pRgANn7cLFCdOOTwJefgK8ef5xMI97aclHzaRwSuCodeYZsifg5u26btwIoIXqgTSVun Tw5dCgzGObGsSXFOGHa8XwTJ6jjKLuelPFfppgW7g6gr8g2E+AslCe0NHEtcrlsoyqagbw 4cFdYCu7vDkYD7n60OEMvc9d7EF3pPc= From: Oliver Upton To: kvmarm@lists.linux.dev Cc: kvm@vger.kernel.org, Marc Zyngier , James Morse , Suzuki K Poulose , Zenghui Yu , Will Deacon , Catalin Marinas , linux-arm-kernel@lists.infradead.org, Gavin Shan , Oliver Upton Subject: [PATCH 2/2] KVM: arm64: Avoid soft lockups due to I-cache maintenance Date: Wed, 20 Sep 2023 08:01:33 +0000 Message-ID: <20230920080133.944717-3-oliver.upton@linux.dev> In-Reply-To: <20230920080133.944717-1-oliver.upton@linux.dev> References: <20230920080133.944717-1-oliver.upton@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Gavin reports of soft lockups on his Ampere Altra Max machine when backing KVM guests with hugetlb pages. Upon further investigation, it was found that the system is unable to keep up with parallel I-cache invalidations done by KVM's stage-2 fault handler. This is ultimately an implementation problem. I-cache maintenance instructions are available at EL0, so nothing stops a malicious userspace from hammering a system with CMOs and cause it to fall over. "Fixing" this problem in KVM is nothing more than slapping a bandage over a much deeper problem. Anyway, the kernel already has a heuristic for limiting TLB invalidations to avoid soft lockups. Reuse that logic to limit I-cache CMOs done by KVM to map executable pages on systems without FEAT_DIC. While at it, restructure __invalidate_icache_guest_page() to improve readability and squeeze our new condition into the existing branching structure. Link: https://lore.kernel.org/kvmarm/20230904072826.1468907-1-gshan@redhat.com/ Signed-off-by: Oliver Upton Reviewed-by: Gavin Shan Tested-by: Gavin Shan --- arch/arm64/include/asm/kvm_mmu.h | 37 ++++++++++++++++++++++++++------ 1 file changed, 31 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h index 96a80e8f6226..a425ecdd7be0 100644 --- a/arch/arm64/include/asm/kvm_mmu.h +++ b/arch/arm64/include/asm/kvm_mmu.h @@ -224,16 +224,41 @@ static inline void __clean_dcache_guest_page(void *va, size_t size) kvm_flush_dcache_to_poc(va, size); } +static inline size_t __invalidate_icache_max_range(void) +{ + u8 iminline; + u64 ctr; + + asm volatile(ALTERNATIVE_CB("movz %0, #0\n" + "movk %0, #0, lsl #16\n" + "movk %0, #0, lsl #32\n" + "movk %0, #0, lsl #48\n", + ARM64_ALWAYS_SYSTEM, + kvm_compute_final_ctr_el0) + : "=r" (ctr)); + + iminline = SYS_FIELD_GET(CTR_EL0, IminLine, ctr) + 2; + return MAX_DVM_OPS << iminline; +} + static inline void __invalidate_icache_guest_page(void *va, size_t size) { - if (icache_is_aliasing()) { - /* any kind of VIPT cache */ + /* + * VPIPT I-cache maintenance must be done from EL2. See comment in the + * nVHE flavor of __kvm_tlb_flush_vmid_ipa(). + */ + if (icache_is_vpipt() && read_sysreg(CurrentEL) != CurrentEL_EL2) + return; + + /* + * Blow the whole I-cache if it is aliasing (i.e. VIPT) or the + * invalidation range exceeds our arbitrary limit on invadations by + * cache line. + */ + if (icache_is_aliasing() || size > __invalidate_icache_max_range()) icache_inval_all_pou(); - } else if (read_sysreg(CurrentEL) != CurrentEL_EL1 || - !icache_is_vpipt()) { - /* PIPT or VPIPT at EL2 (see comment in __kvm_tlb_flush_vmid_ipa) */ + else icache_inval_pou((unsigned long)va, (unsigned long)va + size); - } } void kvm_set_way_flush(struct kvm_vcpu *vcpu);