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 3212A3054EB for ; Thu, 16 Oct 2025 11:09:06 +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=1760612954; cv=none; b=Xwo4jNpelOIAge6NWA+tm7lrKblCpKt+mJUnJfcK+hl3MLJ2v9iXvm/i9gfvZa+R0kQSSWLf6I3vlhuWKM4JcLP9Prd34u3W51ZSot60wQWZrdP7J94E1/NMncxNe1nzZDQkE07yuv6FZpcRaSIHEaiwm9gxxvjRAjpjzi4oCWc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760612954; c=relaxed/simple; bh=DyFXdKIJtSaZzIHhc8DAQo4k9g45sC+S6NNEFpDq338=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YhFYrI1971SDReuMXScpi7Dmf8U09zyeXJVzNO2qdTljayI2yoxIMhaIWVAzDaCeUel0DJSmfzScEZBOxBB7qU3MTrBpVPCMrMowog5CtZH+H4fGdNpVrJAlTqryXZI3I/eNTQp02dXh+LPsJ6Xv3QSiiGYRNBAuvGU1yHKMfkM= 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=b581nttR; 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="b581nttR" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=DyFXdKIJtSaZzIHhc8DAQo4k9g45sC+S6NNEFpDq338=; b=b581nttR4lqlXL3PXUD/qoKwAp mOwW52sp8Qf5IjjeZAS5XI2fZrO4IR5iRvYyfLNjTwPFbWhKIqjjLD7mAEfCMbXAn2yJwB0dHjD/m VV7XCDAgmrWevcT3VmJNDM2CD+cf4V07pR4PZEeOQwe7wihDXVaznGNDOZF7XMQI3bmqW/Oi6heR5 nYKLtsCTLRnnUXyue97rPXHv4sn90ftlMSuj8j42VePAe0PCuDM8QflJhwyeIbwIkgVvSeE4j7CcT /tzpGQD/w1Y5VXvyBlr6ZnpkgWLl225KWUTIBfiyJDKKDqR8jSQumNGVnEr2x0Zvw45gad2TIvK/d Iv1QS2EQ==; 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 1v9Lqq-00000006hJy-19jJ; Thu, 16 Oct 2025 11:08:56 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 808BD30023C; Thu, 16 Oct 2025 13:08:55 +0200 (CEST) Date: Thu, 16 Oct 2025 13:08:55 +0200 From: Peter Zijlstra To: David Kaplan Cc: Thomas Gleixner , Borislav Petkov , Josh Poimboeuf , Pawan Gupta , Ingo Molnar , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Alexander Graf , Boris Ostrovsky , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 31/56] x86/alternative: Prepend nops with retpolines Message-ID: <20251016110855.GO1386988@noisy.programming.kicks-ass.net> References: <20251013143444.3999-1-david.kaplan@amd.com> <20251013143444.3999-32-david.kaplan@amd.com> <20251016103233.GC3289052@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251016103233.GC3289052@noisy.programming.kicks-ass.net> On Thu, Oct 16, 2025 at 12:32:33PM +0200, Peter Zijlstra wrote: > Alas, some micro-archs have significant decode penalties for >3 > prefixes, and filling 6 bytes will need 4 prefixes :-( N/m this, because if it has 6 bytes, then the indirect call will need 3 bytes and we're back to needing 3 prefixes.