From nobody Sat Apr 18 07:47:31 2026 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 40E24C433EF for ; Fri, 15 Jul 2022 11:49:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234739AbiGOLtm (ORCPT ); Fri, 15 Jul 2022 07:49:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43880 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229475AbiGOLti (ORCPT ); Fri, 15 Jul 2022 07:49:38 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DD4A5371AD for ; Fri, 15 Jul 2022 04:49:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657885777; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=ie8S/4kslSZgdmx6wrSNJRQWWqTbqopyobh+d0XIkq8=; b=LMB5TmBpk793gob/kfQTpstn4BGOJfSVXPWC7GL7gDbon9g7A4dxxv6tSj5B4V/Zorp9fU P3y7OVeZM30UdC9vKBaa6XNnUi2NmsEpcE6u89V70itJy9//xaJSd9ROHK7DYGSUrTngAw dZZNKpbw7da/Wbi9gWcybpBqNG54fRw= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-644-seCiYla0MFacY20sMg_2JA-1; Fri, 15 Jul 2022 07:49:27 -0400 X-MC-Unique: seCiYla0MFacY20sMg_2JA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 67777801590; Fri, 15 Jul 2022 11:49:27 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 397E5140EBE3; Fri, 15 Jul 2022 11:49:27 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: x86@kernel.org, peterz@infradead.org, bp@suse.de, Linus Torvalds Subject: [PATCH] KVM: emulate: do not adjust size of fastop and setcc subroutines Date: Fri, 15 Jul 2022 07:49:27 -0400 Message-Id: <20220715114927.1460356-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Instead of doing complicated calculations to find the size of the subroutin= es (which are even more complicated because they need to be stringified into an asm statement), just hardcode to 16. It is less dense for a few combinations of IBT/SLS/retbleed, but it has the advantage of being really simple. Suggested-by: Linus Torvalds Signed-off-by: Paolo Bonzini Acked-by: Borislav Petkov --- arch/x86/kvm/emulate.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 0a15b0fec6d9..f8382abe22ff 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -189,13 +189,6 @@ #define X8(x...) X4(x), X4(x) #define X16(x...) X8(x), X8(x) =20 -#define NR_FASTOP (ilog2(sizeof(ulong)) + 1) -#define RET_LENGTH (1 + (4 * IS_ENABLED(CONFIG_RETHUNK)) + \ - IS_ENABLED(CONFIG_SLS)) -#define FASTOP_LENGTH (ENDBR_INSN_SIZE + 7 + RET_LENGTH) -#define FASTOP_SIZE (8 << ((FASTOP_LENGTH > 8) & 1) << ((FASTOP_LENGTH > 1= 6) & 1)) -static_assert(FASTOP_LENGTH <=3D FASTOP_SIZE); - struct opcode { u64 flags; u8 intercept; @@ -310,9 +303,15 @@ static void invalidate_registers(struct x86_emulate_ct= xt *ctxt) * Moreover, they are all exactly FASTOP_SIZE bytes long, so functions for * different operand sizes can be reached by calculation, rather than a ju= mp * table (which would be bigger than the code). + * + * The 16 byte alignment, considering 5 bytes for the RET thunk, 3 for END= BR + * and 1 for the straight line speculation INT3, leaves 7 bytes for the + * body of the function. Currently none is larger than 4. */ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop); =20 +#define FASTOP_SIZE 16 + #define __FOP_FUNC(name) \ ".align " __stringify(FASTOP_SIZE) " \n\t" \ ".type " name ", @function \n\t" \ @@ -446,9 +445,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop= _t fop); * RET | JMP __x86_return_thunk [1,5 bytes; CONFIG_RETHUNK] * INT3 [1 byte; CONFIG_SLS] */ -#define SETCC_LENGTH (ENDBR_INSN_SIZE + 3 + RET_LENGTH) -#define SETCC_ALIGN (4 << ((SETCC_LENGTH > 4) & 1) << ((SETCC_LENGTH > 8) = & 1)) -static_assert(SETCC_LENGTH <=3D SETCC_ALIGN); +#define SETCC_ALIGN 16 =20 #define FOP_SETCC(op) \ ".align " __stringify(SETCC_ALIGN) " \n\t" \ --=20 2.31.1