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[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: linux-doc@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