From: David Laight <david.laight.linux@gmail.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
x86@kernel.org, Jon Kohler <jon@nutanix.com>,
Nikolay Borisov <nik.borisov@suse.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
David Kaplan <david.kaplan@amd.com>,
Sean Christopherson <seanjc@google.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
KP Singh <kpsingh@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
David Ahern <dsahern@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Asit Mallick <asit.k.mallick@intel.com>,
Tao Zhang <tao1.zhang@intel.com>,
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
Date: Thu, 26 Mar 2026 10:45:57 +0000 [thread overview]
Message-ID: <20260326104557.24295cbb@pumpkin> (raw)
In-Reply-To: <20260326100120.GAacUD8BVziYzLxZHB@fat_crate.local>
On Thu, 26 Mar 2026 11:01:20 +0100
Borislav Petkov <bp@alien8.de> 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
next prev parent reply other threads:[~2026-03-26 10:46 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-24 18:16 [PATCH v8 00/10] VMSCAPE optimization for BHI variant Pawan Gupta
2026-03-24 18:16 ` [PATCH v8 01/10] x86/bhi: x86/vmscape: Move LFENCE out of clear_bhb_loop() Pawan Gupta
2026-03-24 20:22 ` Borislav Petkov
2026-03-24 21:30 ` Pawan Gupta
2026-03-24 18:16 ` [PATCH v8 02/10] x86/bhi: Make clear_bhb_loop() effective on newer CPUs Pawan Gupta
2026-03-24 20:59 ` Borislav Petkov
2026-03-24 22:13 ` Pawan Gupta
2026-03-25 20:37 ` Borislav Petkov
2026-03-25 22:40 ` David Laight
2026-03-26 8:39 ` Pawan Gupta
2026-03-26 9:15 ` David Laight
2026-03-26 10:01 ` Borislav Petkov
2026-03-26 10:45 ` David Laight [this message]
2026-03-25 17:50 ` Jim Mattson
2026-03-25 18:44 ` Pawan Gupta
2026-03-25 19:41 ` David Laight
2026-03-25 22:29 ` Pawan Gupta
2026-03-24 18:17 ` [PATCH v8 03/10] x86/bhi: Rename clear_bhb_loop() to clear_bhb_loop_nofence() Pawan Gupta
2026-03-24 18:17 ` [PATCH v8 04/10] x86/vmscape: Rename x86_ibpb_exit_to_user to x86_predictor_flush_exit_to_user Pawan Gupta
2026-03-24 18:17 ` [PATCH v8 05/10] x86/vmscape: Move mitigation selection to a switch() Pawan Gupta
2026-03-24 18:17 ` [PATCH v8 06/10] x86/vmscape: Use write_ibpb() instead of indirect_branch_prediction_barrier() Pawan Gupta
2026-03-24 18:18 ` [PATCH v8 07/10] x86/vmscape: Use static_call() for predictor flush Pawan Gupta
2026-03-24 19:09 ` bot+bpf-ci
2026-03-24 19:51 ` Pawan Gupta
2026-03-24 18:18 ` [PATCH v8 08/10] x86/vmscape: Deploy BHB clearing mitigation Pawan Gupta
2026-03-24 19:09 ` bot+bpf-ci
2026-03-24 19:46 ` Pawan Gupta
2026-03-24 18:18 ` [PATCH v8 09/10] x86/vmscape: Resolve conflict between attack-vectors and vmscape=force Pawan Gupta
2026-03-24 18:19 ` [PATCH v8 10/10] x86/vmscape: Add cmdline vmscape=on to override attack vector controls Pawan Gupta
2026-03-24 19:09 ` bot+bpf-ci
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