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: Wed, 25 Mar 2026 22:40:18 +0000 [thread overview]
Message-ID: <20260325224018.34714c6e@pumpkin> (raw)
In-Reply-To: <20260325203759.GCacRHp2t8a7c4Bp6E@fat_crate.local>
On Wed, 25 Mar 2026 21:37:59 +0100
Borislav Petkov <bp@alien8.de> wrote:
> On Tue, Mar 24, 2026 at 03:13:08PM -0700, Pawan Gupta wrote:
...
> > Although call to clear_bhb_loop() will be inserted at the end of the BPF
> > program before it returns, I am not sure if it is safe to assume that
> > trashing registers in the path clear_bhb_loop() -> __clear_bhb_loop() is
> > okay? Especially, when we don't know what code compiler generated for
> > clear_bhb_loop(). BPF experts would know better?
>
> The compiler would preserve the regs. If you write it in asm and you adhere to
> the C ABI, you could preserve them too. Shouldn't be too many.
The BPF code that calls it doesn't use the C ABI - it just puts
a call instruction in the code it generates.
Hence all registers must be preserved.
David
>
> Thx.
>
>
next prev parent reply other threads:[~2026-03-25 22:40 UTC|newest]
Thread overview: 40+ 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 [this message]
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
2026-03-26 20:29 ` Pawan Gupta
2026-03-28 0:42 ` Pawan Gupta
2026-03-28 10:08 ` David Laight
2026-04-01 8:12 ` Pawan Gupta
2026-04-01 9:02 ` David Laight
2026-04-01 18:52 ` Pawan Gupta
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
2026-03-31 17:50 ` Sean Christopherson
2026-04-01 8:13 ` 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
2026-03-30 3:16 ` [PATCH v8 00/10] VMSCAPE optimization for BHI variant Jon Kohler
2026-03-30 16:11 ` Pawan Gupta
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