From patchwork Wed Jun 26 07:37:19 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Amit Shah X-Patchwork-Id: 13712375 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 AD8721FBB; Wed, 26 Jun 2024 07:37:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719387455; cv=none; b=q2FrthtLFHTUixRtxswg9sC8GZlkfRt+oYbT2YQ0cIuwjWpQjsWZ2ohKkul02icY29on53y8tRlP4p4Y/UD9X3l9ppz4VzeawAJxVLaaWLRKJUL9nM9egDXxgfa9WTFDcTAsW60xM09YimL0CHHWnlDSs8KqE3wkyCXt68EOAA8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719387455; c=relaxed/simple; bh=ndOzFlNF7mgXZbFomdTEHkww/+uY25Qtzri+zDpcuNU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=DnOeX7IQQkhygJz9q3N2BuTq6udat8f3pF2W+BgKCqo+gmwNHKSVbRyiGjd4sCr1Dxv/k6ishLCIvQF5G3XwK9mrmCXFrC9vQXALQbjHEo2CG13gkhEzbGukrTSnzGsti/NtEGAacikMPRbkLVttjkHFPY/MCvP+1xuciInqNYA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LTSGT5eJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LTSGT5eJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 903C5C32789; Wed, 26 Jun 2024 07:37:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719387455; bh=ndOzFlNF7mgXZbFomdTEHkww/+uY25Qtzri+zDpcuNU=; h=From:To:Cc:Subject:Date:From; b=LTSGT5eJpaTgQVTluRtjprVjIcx53X7vmbk1X7v+8wg93zEvg+wfgByOPa2yjy4Aq isnyIW4pGbQ9hZTyoRjVCtHzkfC8d2jQHzUJrYUGhIVwNZ2b4hyAv5jd+aEMgmGEj3 xmFuYL2l5mF42JYtCjwMrGcOzrJ1bEz2A2c4R0ecUYjQAE/OeTT7T6t11zHwTVsSj7 Xe6fgdpTYunXVod1KtwtENq3wJx89AzVH2UkCJf9mzBLjoDEaMtjgzcsVmovTkeKLu FSPtXdzza1bzyhaSWyYh7q7y8weh/yGVRBQ1Qaepj0MqV9NpFE9ZCDNdHel4+Nqyth BGFfrj+djDicg== From: Amit Shah To: seanjc@google.com, pbonzini@redhat.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: amit.shah@amd.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, kim.phillips@amd.com, david.kaplan@amd.com Subject: [PATCH v2] KVM: SVM: let alternatives handle the cases when RSB filling is required Date: Wed, 26 Jun 2024 09:37:19 +0200 Message-ID: <20240626073719.5246-1-amit@kernel.org> X-Mailer: git-send-email 2.45.2 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Amit Shah Remove superfluous RSB filling after a VMEXIT when the CPU already has flushed the RSB after a VMEXIT when AutoIBRS is enabled. The initial implementation for adding RETPOLINES added an ALTERNATIVES implementation for filling the RSB after a VMEXIT in commit 117cc7a908c836 ("x86/retpoline: Fill return stack buffer on vmexit") Later, X86_FEATURE_RSB_VMEXIT was added in commit 2b129932201673 ("x86/speculation: Add RSB VM Exit protections") The AutoIBRS (on AMD CPUs) feature implementation added in commit e7862eda309ecf ("x86/cpu: Support AMD Automatic IBRS") used the already-implemented logic for EIBRS in spectre_v2_determine_rsb_fill_type_on_vmexit() -- but did not update the code at VMEXIT to act on the mode selected in that function -- resulting in VMEXITs continuing to clear the RSB when RETPOLINES are enabled, despite the presence of AutoIBRS. Signed-off-by: Amit Shah --- v2: - tweak commit message re: Boris's comments. --- arch/x86/kvm/svm/vmenter.S | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S index a0c8eb37d3e1..2ed80aea3bb1 100644 --- a/arch/x86/kvm/svm/vmenter.S +++ b/arch/x86/kvm/svm/vmenter.S @@ -209,10 +209,8 @@ SYM_FUNC_START(__svm_vcpu_run) 7: vmload %_ASM_AX 8: -#ifdef CONFIG_MITIGATION_RETPOLINE /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */ - FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE -#endif + FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT /* Clobbers RAX, RCX, RDX. */ RESTORE_HOST_SPEC_CTRL @@ -348,10 +346,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run) 2: cli -#ifdef CONFIG_MITIGATION_RETPOLINE /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */ - FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE -#endif + FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT /* Clobbers RAX, RCX, RDX, consumes RDI (@svm) and RSI (@spec_ctrl_intercepted). */ RESTORE_HOST_SPEC_CTRL