From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f53.google.com (mail-wm1-f53.google.com [209.85.128.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 89AAC31A07F for ; Thu, 26 Mar 2026 10:46:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.53 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774521962; cv=none; b=EfiBYhw24FlEObQyFCrtL1S3OdJ8/Er+qjUZy+HFZPuv1O2oFpJP/EyihId8Q4SBIYjMJSnaWbjYqAOsZpQVrsOPtbETQjSmFBUkuaJLDo+tX828UGafD4n6HL2beXywIaPZU/IcdzdpLKGvxIh1G5a+TLFVhbEBYi93WA2iQfE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774521962; c=relaxed/simple; bh=64Fas5hYKuMJHCmYPOt+8bmUOjahEq8MaPoJMlkt2pw=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=D9wO+0LF8oGP9V64HpVYG6xD2RwKDrjLtPuKnS2cBB4Ma17Qs+PTmMGSpHmEOu2ayIMy/uKmIil7pZpuixgcWPvFxhleZNKeYCwwGsikRF75hDXxJVw/5EJzcacyB762llCijdQ9jZt1ekUnrz3oG8rEPWMKXWWeN++FS5jnKoc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=hLI58UJ8; arc=none smtp.client-ip=209.85.128.53 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hLI58UJ8" Received: by mail-wm1-f53.google.com with SMTP id 5b1f17b1804b1-486b96760easo8578225e9.2 for ; Thu, 26 Mar 2026 03:46:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1774521960; x=1775126760; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=uWeS487NzYUaa3hGKWOyH/n+tSqTSbzSaVNvnjqb4bk=; b=hLI58UJ8v2QepCbMQ7JXS34BNPDhv0dCXKaAHRysAX/8YJJ5cIP4FVXpB5Dj7sVUsj c7zeZDyRI2tLXE4fRHkuju7HFVHxZFEwouQq6R49k2w53PL/shhfNNzk6wDTbkFyXEve 5SfNlCSRmeBRfnzPdf36kfW5+5lnEYBj4EMvoOyqMDWfvenhSQIfiNm3ggi4ZmntM7ot HCogKDoNDiuGehloKtT4Oygmb1LvkNv7k452N1cZ/tVd3k+U6cuGuCOsVxoIOzVD4ifk biF43fIKqPSOGULHXaI/prV96Bp+hQnBG386+/m6WOVv3jojVD4Yx5ce0nlhbEZTZ8Gm lR4A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1774521960; x=1775126760; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=uWeS487NzYUaa3hGKWOyH/n+tSqTSbzSaVNvnjqb4bk=; b=T5i6mjmEbnuB5FtYRRHwVaXtYx63dVZ7StAiqmwkTsGW+7zP26dR1pw8nV8wP9frt1 IEOpDhQlYDCn30VCJMLMiPezJzXLHTKAUp/s6qJdx8Ub8WaPL1fPVzE6/HtVe9RObz9H GLYgM1/yG7JqLnEVquHnv/RaMbAAYr5de8n527HqufRZiuh3rglrTRN4qJAJSXPbKFFy /nym8HfJUQ/TyWmkbntLR5cslCEr6HpB7Jc7TRpiJJB6YNMDzDx3wgOxBt8U1TEyYIXL Q3PNWSr0vQsJGREXIyMADhMTNwBStp0udILZkcTnYvlVejCzAXCmpvhEHufyEWHHBaFc +yyA== X-Forwarded-Encrypted: i=1; AJvYcCUupbqPz3GIqWEo3qW6Jc7zSQt2+TpuhBBIjlnR0MNshi0lQ4F0w8Q0A0ljOBKy+eIUcB4=@vger.kernel.org X-Gm-Message-State: AOJu0YzUlepQoGIkGBKG3V9wls6eyhBaT7owkCWIppGnNjlG7OX0x6Cd TxHNPsy7IMHvPZ5a3VfrsxJBsocowehTkjM/Ppv24JtpdqlqqzztS5zG X-Gm-Gg: ATEYQzy8vqceAwg70fU1a0yHinqYBikArniPVTEFcGbIT9el8HwAHNvOKtSW/zmTEcc Z1ekuPB0R8ZaXjAcgDNkwKkG5ZmF5farhghavhQ/pG/y2Cj6eLsHu1eoXrrxZbsWdoQhb/FUfyK 2Krp8pRr5+anYph2QikXVM/iecxgLrWIDze92PmeDQRj9o5EndxmloQHxi+EqbUKze0NV76p8CV jtDmEI3vk4rqiuy913pFBYpBBivgSkz1qATeVEoHWPIDegd0CwBKRhY9ydpaz/YW862S5k7wBvD HwU1NIQG1vG4nZAdswCfpsGEjiQiBog3u/r5RieHDFrP2Gd1VDdz/FBS3KsUxKt96tezMec1Igb xQAlPFehoYQXzABYQyAMqc8SSQv1Kf68p+NezlIzYa7jC6iMRbbo1WkX0ojvzYopRcNk2VlXRrw FahMX4ljZcJetYyuOrysVKC7NsQ0BsVbEB0P9F21SShvTTyzoYO1D9MuXL4rpxwUbL X-Received: by 2002:a05:600c:8b31:b0:485:30f7:6e88 with SMTP id 5b1f17b1804b1-487160881a5mr109891615e9.31.1774521959596; Thu, 26 Mar 2026 03:45:59 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43b919df6d4sm6790010f8f.25.2026.03.26.03.45.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 03:45:59 -0700 (PDT) Date: Thu, 26 Mar 2026 10:45:57 +0000 From: David Laight To: Borislav Petkov Cc: Pawan Gupta , x86@kernel.org, Jon Kohler , Nikolay Borisov , "H. Peter Anvin" , Josh Poimboeuf , David Kaplan , Sean Christopherson , Dave Hansen , Peter Zijlstra , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , KP Singh , Jiri Olsa , "David S. Miller" , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , David Ahern , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , Stanislav Fomichev , Hao Luo , Paolo Bonzini , Jonathan Corbet , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Asit Mallick , Tao Zhang , bpf@vger.kernel.org, netdev@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v8 02/10] x86/bhi: Make clear_bhb_loop() effective on newer CPUs Message-ID: <20260326104557.24295cbb@pumpkin> In-Reply-To: <20260326100120.GAacUD8BVziYzLxZHB@fat_crate.local> References: <20260324-vmscape-bhb-v8-0-68bb524b3ab9@linux.intel.com> <20260324-vmscape-bhb-v8-2-68bb524b3ab9@linux.intel.com> <20260324205930.GQacL7Mp7vwGBKX1W7@fat_crate.local> <20260324221308.7sh6afdy6r6tsf4w@desk> <20260325203759.GCacRHp2t8a7c4Bp6E@fat_crate.local> <20260326083934.fk4wyhe6rgiss34z@desk> <20260326100120.GAacUD8BVziYzLxZHB@fat_crate.local> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 26 Mar 2026 11:01:20 +0100 Borislav Petkov wrote: > On Thu, Mar 26, 2026 at 01:39:34AM -0700, Pawan Gupta wrote: > > I believe the equivalent for cpu_feature_enabled() in asm is the > > ALTERNATIVE. Please let me know if I am missing something. > > Yes, you are. > > The point is that you don't want to stick those alternative calls inside some > magic bhb_loop function but hand them in from the outside, as function > arguments. > > Basically what I did. > > Then you were worried about this being C code and it had to be noinstr... So > that outer function can be rewritten in asm, I think, and still keep it well > separate. > > I'll try to rewrite it once I get a free minute, and see how it looks. > I think someone tried getting C code to write the values to global data and getting the asm to read them. That got discounted because it spilt things between two largely unrelated files. I think the BPF code would need significant refactoring to call a C function. David