From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 E972B2AE90; Tue, 30 Sep 2025 12:52:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759236729; cv=none; b=jkEfi/J3RQV5PDoCu9ZOGJf5f+IBGeB3m/mwM/gPCqWJX+BWEs83crZIkG5k4H2xk78VaoW2+TTIO06ksXR00BNzXnw2oYuxgv1oUwiWx7jCkI8+lHcFW/1lP1aCTSoSIPKIusKNtMMoF9rhWuhA7SK2HO7CbQCeAaqEiXYj5cc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759236729; c=relaxed/simple; bh=NBzs5D4uuWJUjPCHsfP6knc6Q/gyHDcuVmc8t+peMmg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MzgsySyQoaMUF3Zss9YToOicMX5ojob/UAfRUgOg9gG0GHzcSeYGrvkiB1bY8zyIwCJyZlocvalVtOPkDIL1mdg8T0Kkm5cCiOzhbHPNKTJvCl0n3bf1vSvzuIu2w/tDHcVp/NpiRkEETk4GA/cyH9GaEKRZFd898IAVjX5mzg8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=YgP4wE0q; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YgP4wE0q" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=1J//rl64lw04ODF0oGXCCZsjqrxoJKz9lbEG9Hm9I+U=; b=YgP4wE0qqX3ifnlrg0BFrYJAtL mGbxN4ktg1xjYBoNO1aJrnzkLQlbIAvQgOUiafQ1I1Wk7iHbx2b/FlwfXd/cl3QQ3rnHkVZWRVXqU UzrY1LIsIND+2QuSXVXyU8hzmEpZcm+e5lWCv+Jegj4oMWxT4i1b9+tIvjQikOp2FVJnCUn8gjvEg /oHf0R71xww7cSPJbGLxbctdozyPj3w10zaC2JxXPE9hIpjiWelxegtIFKGK7neJNOxT9fvrQKDmL ycLwMA+/Y17U8NPGGUc8sobLLnZVb64iN9e+wO+gmBaApkpCxG3h6NWoyD3ZfmwtAufavR357hQgl VShkrpLA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1v3Zpl-0000000Cq3s-2JQ3; Tue, 30 Sep 2025 12:51:57 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 9A26F300220; Tue, 30 Sep 2025 14:51:56 +0200 (CEST) Date: Tue, 30 Sep 2025 14:51:56 +0200 From: Peter Zijlstra To: =?iso-8859-1?Q?J=FCrgen_Gro=DF?= Cc: linux-kernel@vger.kernel.org, x86@kernel.org, llvm@lists.linux.dev, xin@zytor.com, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt Subject: Re: [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for WRMSR Message-ID: <20250930125156.GK1386988@noisy.programming.kicks-ass.net> References: <20250930070356.30695-1-jgross@suse.com> <20250930070356.30695-10-jgross@suse.com> <20250930083137.GH3245006@noisy.programming.kicks-ass.net> <2df26cc0-53bc-499c-8c78-bc24fd8bf882@suse.com> <20250930085044.GK3245006@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250930085044.GK3245006@noisy.programming.kicks-ass.net> On Tue, Sep 30, 2025 at 10:50:44AM +0200, Peter Zijlstra wrote: > On Tue, Sep 30, 2025 at 10:46:23AM +0200, Jürgen Groß wrote: > > > asm_inline volatile goto( > > > "1:\n" > > > ALTERNATIVE(PREPARE_RCX_RDX_FOR_WRMSR > > > "2:\n" > > > ALTERNATIVE("ds wrmsr", > > > ASM_WRMSRNS, X86_FEATURE_WRMSRNS), > > > ASM_WRMSRNS_IMM, X86_FEATURE_MSR_IMM); > > > _ASM_EXTABLE_TYPE(1b, %l[badmsr], %c[type]) /* For WRMSRNS immediate */ > > > _ASM_EXTABLE_TYPE(2b, %l[badmsr], %c[type]) /* For WRMSR(NS) */ > > > > > > : > > > : [val] "a" (val), [msr] "i" (msr), [type] "i" (type) > > > : "memory", "ecx", "rdx" > > > : badmsr); > > > > Oh well, lets forget about this :-) So I couldn't. I tried the below, which when building a .i generates the following: static inline __attribute__((__gnu_inline__)) __attribute__((__unused__)) __attribute__((no_instrument_function)) void clear_page(void *page) { kmsan_unpoison_memory(page, ((1UL) << 12)); asm __inline volatile( "# ALT: oldinstr\n" "__UNIQUE_ID_altinstr_9" "_begin:\n\t" "# ALT: oldinstr\n" "__UNIQUE_ID_altinstr_8" "_begin:\n\t" "call %c[old]" "\n" "__UNIQUE_ID_altinstr_8" "_pad:\n" "# ALT: padding\n" ".skip -(((" "__UNIQUE_ID_altinstr_8" "_alt_end - " "__UNIQUE_ID_altinstr_8" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_8" "_pad - " "__UNIQUE_ID_altinstr_8" "_begin" ")) > 0) * " "((" "__UNIQUE_ID_altinstr_8" "_alt_end - " "__UNIQUE_ID_altinstr_8" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_8" "_pad - " "__UNIQUE_ID_altinstr_8" "_begin" ")),0x90\n" "__UNIQUE_ID_altinstr_8" "_end:\n" ".pushsection .altinstructions,\"a\"\n" " .long " "__UNIQUE_ID_altinstr_8" "_begin - .\n" " .long " "__UNIQUE_ID_altinstr_8" "_alt_begin - .\n" " .4byte " "( 3*32+16)" "\n" " .byte " "__UNIQUE_ID_altinstr_8" "_end - " "__UNIQUE_ID_altinstr_8" "_begin" "\n" " .byte " "__UNIQUE_ID_altinstr_8" "_alt_end - " "__UNIQUE_ID_altinstr_8" "_alt_begin" "\n" ".popsection\n" ".pushsection .altinstr_replacement, \"ax\"\n" "# ALT: replacement\n" "__UNIQUE_ID_altinstr_8" "_alt_begin:\n\t" "call %c[new1]" "\n" "__UNIQUE_ID_altinstr_8" "_alt_end:\n" ".popsection\n" "\n" "__UNIQUE_ID_altinstr_9" "_pad:\n" "# ALT: padding\n" ".skip -(((" "__UNIQUE_ID_altinstr_9" "_alt_end - " "__UNIQUE_ID_altinstr_9" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_9" "_pad - " "__UNIQUE_ID_altinstr_9" "_begin" ")) > 0) * " "((" "__UNIQUE_ID_altinstr_9" "_alt_end - " "__UNIQUE_ID_altinstr_9" "_alt_begin" ")-(" "__UNIQUE_ID_altinstr_9" "_pad - " "__UNIQUE_ID_altinstr_9" "_begin" ")),0x90\n" "__UNIQUE_ID_altinstr_9" "_end:\n" ".pushsection .altinstructions,\"a\"\n" " .long " "__UNIQUE_ID_altinstr_9" "_begin - .\n" " .long " "__UNIQUE_ID_altinstr_9" "_alt_begin - .\n" " .4byte " "( 9*32+ 9)" "\n" " .byte " "__UNIQUE_ID_altinstr_9" "_end - " "__UNIQUE_ID_altinstr_9" "_begin" "\n" " .byte " "__UNIQUE_ID_altinstr_9" "_alt_end - " "__UNIQUE_ID_altinstr_9" "_alt_begin" "\n" ".popsection\n" ".pushsection .altinstr_replacement, \"ax\"\n" "# ALT: replacement\n" "__UNIQUE_ID_altinstr_9" "_alt_begin:\n\t" "call %c[new2]" "\n" "__UNIQUE_ID_altinstr_9" "_alt_end:\n" ".popsection\n" : "+r" (current_stack_pointer), "=D" (page) : [old] "i" (clear_page_orig), [new1] "i" (clear_page_rep), [new2] "i" (clear_page_erms) , "D" (page) : "cc", "memory", "rax", "rcx") ; } Which looks right, but utterly fails to build :( diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 15bc07a5ebb3..12a93982457a 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -5,6 +5,7 @@ #include #include #include +#include #include #include @@ -184,38 +185,41 @@ static inline int alternatives_text_reserved(void *start, void *end) #define ALT_CALL_INSTR "call BUG_func" -#define alt_slen "772b-771b" -#define alt_total_slen "773b-771b" -#define alt_rlen "775f-774f" +#define alt_slen(pfx) #pfx "_pad - " #pfx "_begin" +#define alt_total_slen(pfx) #pfx "_end - " #pfx "_begin" +#define alt_rlen(pfx) #pfx "_alt_end - " #pfx "_alt_begin" -#define OLDINSTR(oldinstr) \ +#define OLDINSTR(oldinstr, pfx) \ "# ALT: oldinstr\n" \ - "771:\n\t" oldinstr "\n772:\n" \ + #pfx "_begin:\n\t" oldinstr "\n" #pfx "_pad:\n" \ "# ALT: padding\n" \ - ".skip -(((" alt_rlen ")-(" alt_slen ")) > 0) * " \ - "((" alt_rlen ")-(" alt_slen ")),0x90\n" \ - "773:\n" + ".skip -(((" alt_rlen(pfx) ")-(" alt_slen(pfx) ")) > 0) * " \ + "((" alt_rlen(pfx) ")-(" alt_slen(pfx) ")),0x90\n" \ + #pfx "_end:\n" -#define ALTINSTR_ENTRY(ft_flags) \ +#define ALTINSTR_ENTRY(ft_flags, pfx) \ ".pushsection .altinstructions,\"a\"\n" \ - " .long 771b - .\n" /* label */ \ - " .long 774f - .\n" /* new instruction */ \ + " .long " #pfx "_begin - .\n" /* label */ \ + " .long " #pfx "_alt_begin - .\n" /* new instruction */ \ " .4byte " __stringify(ft_flags) "\n" /* feature + flags */ \ - " .byte " alt_total_slen "\n" /* source len */ \ - " .byte " alt_rlen "\n" /* replacement len */ \ + " .byte " alt_total_slen(pfx) "\n" /* source len */ \ + " .byte " alt_rlen(pfx) "\n" /* replacement len */ \ ".popsection\n" -#define ALTINSTR_REPLACEMENT(newinstr) /* replacement */ \ +#define ALTINSTR_REPLACEMENT(newinstr, pfx) /* replacement */ \ ".pushsection .altinstr_replacement, \"ax\"\n" \ "# ALT: replacement\n" \ - "774:\n\t" newinstr "\n775:\n" \ + #pfx "_alt_begin:\n\t" newinstr "\n" #pfx "_alt_end:\n" \ ".popsection\n" /* alternative assembly primitive: */ -#define ALTERNATIVE(oldinstr, newinstr, ft_flags) \ - OLDINSTR(oldinstr) \ - ALTINSTR_ENTRY(ft_flags) \ - ALTINSTR_REPLACEMENT(newinstr) +#define __ALTERNATIVE(oldinstr, newinstr, ft_flags, pfx) \ + OLDINSTR(oldinstr, pfx) \ + ALTINSTR_ENTRY(ft_flags, pfx) \ + ALTINSTR_REPLACEMENT(newinstr, pfx) + +#define ALTERNATIVE(oldinstr, newinstr, feat) \ + __ALTERNATIVE(oldinstr, newinstr, feat, __UNIQUE_ID(altinstr)) #define ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \ ALTERNATIVE(ALTERNATIVE(oldinstr, newinstr1, ft_flags1), newinstr2, ft_flags2) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 64ff73c533e5..d79552a61fda 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -163,7 +163,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, __asm__ ("" : "=r" (var) : "0" (var)) #endif -#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__) +#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__PASTE(__UNIQUE_ID_, prefix), _), __COUNTER__) /** * data_race - mark an expression as containing intentional data races