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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7704C433F5 for ; Fri, 19 Nov 2021 10:27:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9A2BA61B6F for ; Fri, 19 Nov 2021 10:27:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234475AbhKSKan (ORCPT ); Fri, 19 Nov 2021 05:30:43 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:34408 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229521AbhKSKan (ORCPT ); Fri, 19 Nov 2021 05:30:43 -0500 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id D972F1FD38; Fri, 19 Nov 2021 10:27:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637317660; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=L6eCp1Ki2R16atpMcyacQdMlX3+DmOGOXg/392jMpR8=; b=SwBGweD9Io4a3bgB8pnPKSVJyQ4tImf6rmrQfe+S36cGbxJ3CKLga1EdsmoevN90tnPVSI pRs8UlCcHwUUhcv8RQuxn5kwc92EvLTxFa5pf3jS4nmLkeRF3CdE9ERlTvDlE0dz0bCpw0 i8L2gGHoSbCBgXstaqDwMbjtRjt+nG4= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 4D25313DD5; Fri, 19 Nov 2021 10:27:40 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id WDlpERx8l2FRDwAAMHmgww (envelope-from ); Fri, 19 Nov 2021 10:27:40 +0000 Subject: Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV To: "Kirill A. Shutemov" , Lai Jiangshan Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Kuppuswamy Sathyanarayanan , Andi Kleen , Dave Hansen , Peter Zijlstra , X86 ML , LKML , "Kirill A. Shutemov" , Deep Shah , "VMware, Inc." References: <20211117181439.4368-1-kirill.shutemov@linux.intel.com> <20211119102048.hjm46edvhryjgluy@box.shutemov.name> From: Juergen Gross Message-ID: <42361b9b-da86-dce2-eb17-fe36c9329347@suse.com> Date: Fri, 19 Nov 2021 11:27:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20211119102048.hjm46edvhryjgluy@box.shutemov.name> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="mDUSDCKFf5hnvoHtKqJ1bvgDAOfKlbLmM" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --mDUSDCKFf5hnvoHtKqJ1bvgDAOfKlbLmM Content-Type: multipart/mixed; boundary="h57Uybr4nq8Mp8UkVlZO54tFnF7w7BV2H"; protected-headers="v1" From: Juergen Gross To: "Kirill A. Shutemov" , Lai Jiangshan Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Kuppuswamy Sathyanarayanan , Andi Kleen , Dave Hansen , Peter Zijlstra , X86 ML , LKML , "Kirill A. Shutemov" , Deep Shah , "VMware, Inc." Message-ID: <42361b9b-da86-dce2-eb17-fe36c9329347@suse.com> Subject: Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV References: <20211117181439.4368-1-kirill.shutemov@linux.intel.com> <20211119102048.hjm46edvhryjgluy@box.shutemov.name> In-Reply-To: <20211119102048.hjm46edvhryjgluy@box.shutemov.name> --h57Uybr4nq8Mp8UkVlZO54tFnF7w7BV2H Content-Type: multipart/mixed; boundary="------------FF60BD8B4DF8F80DFE2BA712" Content-Language: en-US This is a multi-part message in MIME format. --------------FF60BD8B4DF8F80DFE2BA712 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 19.11.21 11:20, Kirill A. Shutemov wrote: > On Fri, Nov 19, 2021 at 03:51:44PM +0800, Lai Jiangshan wrote: >> On Thu, Nov 18, 2021 at 7:14 AM Kirill A. Shutemov wrote: >>> >>> TDX is going to use CONFIG_PARAVIRT_XXL, but kernel fails to compile = if >>> XEN_PV is not enabled: >>> >>> ld.lld: error: undefined symbol: xen_iret >>> >>> It happens because INTERRUPT_RETURN defined to use xen_iret if >>> CONFIG_PARAVIRT_XXL enabled regardless of CONFIG_XEN_PV. >>> >>> The issue is not visible in the current kernel because CONFIG_XEN_PV = is >>> the only user of CONFIG_PARAVIRT_XXL and there's no way to enable the= m >>> separately. >>> >>> Rework code to define INTERRUPT_RETURN based on CONFIG_XEN_PV, not >>> CONFIG_PARAVIRT_XXL. >>> >>> Signed-off-by: Kirill A. Shutemov >>> Cc: Juergen Gross >>> Cc: Deep Shah >>> Cc: "VMware, Inc." >>> --- >>> arch/x86/include/asm/irqflags.h | 7 +++++-- >>> arch/x86/include/asm/paravirt.h | 5 ----- >>> 2 files changed, 5 insertions(+), 7 deletions(-) >>> >>> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/i= rqflags.h >>> index b794b6da3214..3b8ddcb7be76 100644 >>> --- a/arch/x86/include/asm/irqflags.h >>> +++ b/arch/x86/include/asm/irqflags.h >>> @@ -118,8 +118,6 @@ static __always_inline unsigned long arch_local_i= rq_save(void) >>> #define SAVE_FLAGS pushfq; popq %rax >>> #endif >>> >>> -#define INTERRUPT_RETURN jmp native_iret >>> - >>> #endif >>> >>> #endif /* __ASSEMBLY__ */ >>> @@ -147,8 +145,13 @@ static __always_inline void arch_local_irq_resto= re(unsigned long flags) >>> #ifdef CONFIG_X86_64 >>> #ifdef CONFIG_XEN_PV >>> #define SWAPGS ALTERNATIVE "swapgs", "", X86_FEATURE_XENPV >>> +#define INTERRUPT_RETURN = \ >>> + ANNOTATE_RETPOLINE_SAFE; = \ >>> + ALTERNATIVE_TERNARY("jmp *paravirt_iret(%rip);", = \ >>> + X86_FEATURE_XENPV, "jmp xen_iret;", "jmp native_iret;= ") >> >> It is part of what CONFIG_PARAVIRT_XXL was designed for to enable >> pv-aware INTERRUPT_RETURN. >=20 > That's very vague statement. >=20 > Could you elaborate on what is wrong with proposed fix? >=20 >> I would prefer xen_iret is defined as a weak symbol unconditionally. >> Like: >> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index e38a4cf795d9..c0953f1b4559 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -635,6 +635,7 @@ SYM_INNER_LABEL_ALIGN(native_iret, SYM_L_GLOBAL) >> jnz native_irq_return_ldt >> #endif >> >> +SYM_INNER_LABEL(xen_iret, SYM_L_WEAK) /* placeholder */ >> SYM_INNER_LABEL(native_irq_return_iret, SYM_L_GLOBAL) >> /* >> * This may fault. Non-paranoid faults on return to userspac= e are >> >> It will work when !CONFIG_XEN_PV >=20 > It pollutes namespace for no particular reason. I don't see it justifie= d. >=20 I agree. IMO weak symbols should be avoided if easily possible, and the patch here shows that it IS possible without any problem. 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