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=-9.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 80A1DC47255 for ; Sun, 10 May 2020 01:48:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 536A720A8B for ; Sun, 10 May 2020 01:48:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="p3hf9Zli" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728986AbgEJBsc (ORCPT ); Sat, 9 May 2020 21:48:32 -0400 Received: from smtp-fw-6001.amazon.com ([52.95.48.154]:13612 "EHLO smtp-fw-6001.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728940AbgEJBsb (ORCPT ); Sat, 9 May 2020 21:48:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1589075309; x=1620611309; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version; bh=TfCbh6Ws4bPSN17KqjjWMeKKKnG2rMNi9Ev0fkWczFs=; b=p3hf9Zli3AD5jJIbFADutUxHA5r4ry1fuCPsZ8+9vI1ocu4bwAkRpoD+ pIY4JPuTSPN3LbL1umkwX5ylsNijZIEVtjdBXb+IS9MIrB5BQEkfK0hfj 1+uou/LyH5AoUZHruxR/Hrn+q1mbbr1tOZ/RomN3D9YdpJ74+KrCrYKIr Q=; IronPort-SDR: cuA/kqCtr1mXVxwbcnhhByUY5S2q9JXtBxskxvB0VRjIPI99fWMxzFC9XXQBrSCK2jrgdHZl8f Awo8q+hnss3Q== X-IronPort-AV: E=Sophos;i="5.73,373,1583193600"; d="scan'208";a="30835695" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-1a-821c648d.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-6001.iad6.amazon.com with ESMTP; 10 May 2020 01:48:20 +0000 Received: from EX13MTAUWA001.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan3.iad.amazon.com [10.40.159.166]) by email-inbound-relay-1a-821c648d.us-east-1.amazon.com (Postfix) with ESMTPS id 5290BA2368; Sun, 10 May 2020 01:48:17 +0000 (UTC) Received: from EX13D01UWA001.ant.amazon.com (10.43.160.60) by EX13MTAUWA001.ant.amazon.com (10.43.160.118) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Sun, 10 May 2020 01:48:16 +0000 Received: from EX13MTAUWC001.ant.amazon.com (10.43.162.135) by EX13d01UWA001.ant.amazon.com (10.43.160.60) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Sun, 10 May 2020 01:48:16 +0000 Received: from localhost (10.85.6.121) by mail-relay.amazon.com (10.43.162.232) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Sun, 10 May 2020 01:48:15 +0000 From: Balbir Singh To: , CC: , , , , , , , Balbir Singh Subject: [PATCH v6 3/6] arch/x86/mm: Refactor cond_ibpb() to support other use cases Date: Sun, 10 May 2020 11:48:00 +1000 Message-ID: <20200510014803.12190-4-sblbir@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200510014803.12190-1-sblbir@amazon.com> References: <20200510014803.12190-1-sblbir@amazon.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org cond_ibpb() has the necessary bits required to track the previous mm in switch_mm_irqs_off(). This can be reused for other use cases like L1D flushing (on context switch out). Suggested-by: Thomas Gleixner Signed-off-by: Balbir Singh --- arch/x86/include/asm/tlbflush.h | 2 +- arch/x86/mm/tlb.c | 43 +++++++++++++++++---------------- 2 files changed, 23 insertions(+), 22 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 8c87a2e0b660..a927d40664df 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -83,7 +83,7 @@ struct tlb_state { /* Last user mm for optimizing IBPB */ union { struct mm_struct *last_user_mm; - unsigned long last_user_mm_ibpb; + unsigned long last_user_mm_spec; }; u16 loaded_mm_asid; diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index cf81902e6992..10056b8d8f01 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -43,10 +43,11 @@ */ /* - * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer which is - * stored in cpu_tlb_state.last_user_mm_ibpb. + * Bits to mangle the TIF_SPEC_IB state into the mm pointer which is + * stored in cpu_tlb_state.last_user_mm_spec. */ #define LAST_USER_MM_IBPB 0x1UL +#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB) /* * The x86 feature is called PCID (Process Context IDentifier). It is similar @@ -345,19 +346,24 @@ static void sync_current_stack_to_mm(struct mm_struct *mm) } } -static inline unsigned long mm_mangle_tif_spec_ib(struct task_struct *next) +static inline unsigned long mm_mangle_tif_spec_bits(struct task_struct *next) { unsigned long next_tif = task_thread_info(next)->flags; - unsigned long ibpb = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_IBPB; + unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK; - return (unsigned long)next->mm | ibpb; + return (unsigned long)next->mm | spec_bits; } -static void cond_ibpb(struct task_struct *next) +static void cond_mitigation(struct task_struct *next) { + unsigned long prev_mm, next_mm; + if (!next || !next->mm) return; + next_mm = mm_mangle_tif_spec_bits(next); + prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_spec); + /* * Both, the conditional and the always IBPB mode use the mm * pointer to avoid the IBPB when switching between tasks of the @@ -368,8 +374,6 @@ static void cond_ibpb(struct task_struct *next) * exposed data is not really interesting. */ if (static_branch_likely(&switch_mm_cond_ibpb)) { - unsigned long prev_mm, next_mm; - /* * This is a bit more complex than the always mode because * it has to handle two cases: @@ -399,20 +403,14 @@ static void cond_ibpb(struct task_struct *next) * Optimize this with reasonably small overhead for the * above cases. Mangle the TIF_SPEC_IB bit into the mm * pointer of the incoming task which is stored in - * cpu_tlbstate.last_user_mm_ibpb for comparison. - */ - next_mm = mm_mangle_tif_spec_ib(next); - prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_ibpb); - - /* + * cpu_tlbstate.last_user_mm_spec for comparison. + * * Issue IBPB only if the mm's are different and one or * both have the IBPB bit set. */ if (next_mm != prev_mm && (next_mm | prev_mm) & LAST_USER_MM_IBPB) indirect_branch_prediction_barrier(); - - this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, next_mm); } if (static_branch_unlikely(&switch_mm_always_ibpb)) { @@ -421,11 +419,12 @@ static void cond_ibpb(struct task_struct *next) * different context than the user space task which ran * last on this CPU. */ - if (this_cpu_read(cpu_tlbstate.last_user_mm) != next->mm) { + if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) != + (unsigned long)next->mm) indirect_branch_prediction_barrier(); - this_cpu_write(cpu_tlbstate.last_user_mm, next->mm); - } } + + this_cpu_write(cpu_tlbstate.last_user_mm_spec, next_mm); } #ifdef CONFIG_PERF_EVENTS @@ -550,8 +549,10 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * Avoid user/user BTB poisoning by flushing the branch * predictor when switching between processes. This stops * one process from doing Spectre-v2 attacks on another. + * The hook can also be used for mitigations that rely + * on switch_mm for hooks. */ - cond_ibpb(tsk); + cond_mitigation(tsk); if (IS_ENABLED(CONFIG_VMAP_STACK)) { /* @@ -677,7 +678,7 @@ void initialize_tlbstate_and_flush(void) write_cr3(build_cr3(mm->pgd, 0)); /* Reinitialize tlbstate. */ - this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, LAST_USER_MM_IBPB); + this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_IBPB); this_cpu_write(cpu_tlbstate.loaded_mm_asid, 0); this_cpu_write(cpu_tlbstate.next_asid, 1); this_cpu_write(cpu_tlbstate.ctxs[0].ctx_id, mm->context.ctx_id); -- 2.17.1