From patchwork Mon May 8 15:47:03 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mathias Krause X-Patchwork-Id: 13234685 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 5F566C77B75 for ; Mon, 8 May 2023 15:47:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234429AbjEHPrq (ORCPT ); Mon, 8 May 2023 11:47:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234116AbjEHPrk (ORCPT ); Mon, 8 May 2023 11:47:40 -0400 Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D12A049F0 for ; Mon, 8 May 2023 08:47:20 -0700 (PDT) Received: by mail-ed1-x536.google.com with SMTP id 4fb4d7f45d1cf-50b383222f7so7142709a12.3 for ; Mon, 08 May 2023 08:47:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=grsecurity.net; s=grsec; t=1683560839; x=1686152839; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=fvMBpYGUUFbOhtoeU6tZl9mcm8XZOcaQ6enJN2RpEHs=; b=ecsq9ypdG7ZRARLjZW8Emx2S8hbt9VVx7CQmTQQ5bVRbcTQ1XQOMmJei2JhIfYngbI sdJ/uk2mG9tpr7zXZ88/TwbUM1FuHhh8r9xWA03phExNboobCL46/QEFH76PQlrPtvV4 mmJDDDpxsfWxgadvfLHS3rHbt5hu8u57XThNC6fWYDaTsyDcWSiubYw/aaLR0ei+eIu/ T/7OMQ65d0aaxy3TVWLl69GFETfPh+Y/pWyrWUgWLhDWT8i9FoHQCJ36calMSBWzBvtG lJYp6h54kd32+XcKED7g/VCJH2hy8Cu3aMVx1eMdEiETmvNerPrnm1qLZcN9bcop0C/a 8MBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1683560839; x=1686152839; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=fvMBpYGUUFbOhtoeU6tZl9mcm8XZOcaQ6enJN2RpEHs=; b=N9rBVGsCZqkt4H3MVuAHYQZCX/KgP21J+ERxuMKEOg7TyWdjQcFZc5VC37TCha3V77 msN1wv21j39sBeijAY/kKh4jf9DA4qjC7RltJ1bEzJENK3FDz+gUQCWkaEKQh+slF7a1 hpmgOGJ5dOV7nDVWwgWDrQvUHA7Lq5M58+0aZCKbmSSPQb7w57SPd7TioBGTcnOvOQ9D gbled+6HZTUfGwWekdcX56+FvfKQQqynW0C6mpZM3aS31xduiaGQf777O2ArjR01E3lg UUZHXQ7Ejp/0CTpLmKcIc5ogGO0uTzgGgNd2ai6CarW+phujxW5jEeB6f38W2Ckn6B+a DONg== X-Gm-Message-State: AC+VfDwHse14NwSCJdvuspQpt7HhwtFYC0yV45rMExiWqK5bEHvzf6k0 wpoM5y5C2WkaWlD6b2pI6K8bgA== X-Google-Smtp-Source: ACHHUZ5/u4SgZ1Df3Vxq+zvKFE+Zqa3Bu3zrMmOOg0tv1QZinxH5syijLyX11+GoDI+9NhhiGWsMtw== X-Received: by 2002:a17:907:ea6:b0:951:f54c:208b with SMTP id ho38-20020a1709070ea600b00951f54c208bmr9167633ejc.24.1683560839338; Mon, 08 May 2023 08:47:19 -0700 (PDT) Received: from localhost.localdomain (p549211c7.dip0.t-ipconnect.de. [84.146.17.199]) by smtp.gmail.com with ESMTPSA id md1-20020a170906ae8100b0094b5ce9d43dsm121822ejb.85.2023.05.08.08.47.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 May 2023 08:47:18 -0700 (PDT) From: Mathias Krause To: stable@vger.kernel.org Cc: Paolo Bonzini , Sean Christopherson , kvm@vger.kernel.org, Mathias Krause Subject: [PATCH 5.15 2/8] KVM: x86: Do not unload MMU roots when only toggling CR0.WP with TDP enabled Date: Mon, 8 May 2023 17:47:03 +0200 Message-Id: <20230508154709.30043-3-minipli@grsecurity.net> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230508154709.30043-1-minipli@grsecurity.net> References: <20230508154709.30043-1-minipli@grsecurity.net> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org [ Upstream commit 01b31714bd90be2784f7145bf93b7f78f3d081e1 ] There is no need to unload the MMU roots with TDP enabled when only CR0.WP has changed -- the paging structures are still valid, only the permission bitmap needs to be updated. One heavy user of toggling CR0.WP is grsecurity's KERNEXEC feature to implement kernel W^X. The optimization brings a huge performance gain for this case as the following micro-benchmark running 'ssdd 10 50000' from rt-tests[1] on a grsecurity L1 VM shows (runtime in seconds, lower is better): legacy TDP shadow kvm-x86/next@d8708b 8.43s 9.45s 70.3s +patch 5.39s 5.63s 70.2s For legacy MMU this is ~36% faster, for TDP MMU even ~40% faster. Also TDP and legacy MMU now both have a similar runtime which vanishes the need to disable TDP MMU for grsecurity. Shadow MMU sees no measurable difference and is still slow, as expected. [1] https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git Signed-off-by: Mathias Krause Link: https://lore.kernel.org/r/20230322013731.102955-3-minipli@grsecurity.net Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Signed-off-by: Mathias Krause --- arch/x86/kvm/x86.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 018f6a394d44..27900d4017a7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -878,6 +878,18 @@ EXPORT_SYMBOL_GPL(load_pdptrs); void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned long cr0) { + /* + * CR0.WP is incorporated into the MMU role, but only for non-nested, + * indirect shadow MMUs. If TDP is enabled, the MMU's metadata needs + * to be updated, e.g. so that emulating guest translations does the + * right thing, but there's no need to unload the root as CR0.WP + * doesn't affect SPTEs. + */ + if (tdp_enabled && (cr0 ^ old_cr0) == X86_CR0_WP) { + kvm_init_mmu(vcpu); + return; + } + if ((cr0 ^ old_cr0) & X86_CR0_PG) { kvm_clear_async_pf_completion_queue(vcpu); kvm_async_pf_hash_reset(vcpu);