From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4BC47FBFD for ; Mon, 15 May 2023 17:01:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F937C433D2; Mon, 15 May 2023 17:01:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1684170114; bh=ODgdSZa33c7HK6Z+zBriefM0XZK50IZWPUrOB5ux364=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CgOQXaiMNURF4D04K1FY2ihfvrlfb2mbjOJrjw7aNOyvHS7MwHRmIqKGg9y6i4xiV ldix72fpr9BLMOU3PMq5AVmxv55nW/hwieWQvLtYdzRvssIS/C+nnlCHgF0vxo0c5k DYwPIjPWeLqP46aILed5YiAPRm3U8zkcM23LVKGg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Mathias Krause , Sean Christopherson , Sasha Levin Subject: [PATCH 6.1 021/239] KVM: x86: Do not unload MMU roots when only toggling CR0.WP with TDP enabled Date: Mon, 15 May 2023 18:24:44 +0200 Message-Id: <20230515161722.224363649@linuxfoundation.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230515161721.545370111@linuxfoundation.org> References: <20230515161721.545370111@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Mathias Krause [ 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 Signed-off-by: Sasha Levin --- 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 3463ef7f30196..d7af225b63d89 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -910,6 +910,18 @@ 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); -- 2.39.2