From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Jim Mattson <jmattson@google.com>
Cc: 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>,
Borislav Petkov <bp@alien8.de>,
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>,
David Laight <david.laight.linux@gmail.com>,
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, chao.gao@intel.com
Subject: Re: [PATCH v9 02/10] x86/bhi: Make clear_bhb_loop() effective on newer CPUs
Date: Fri, 3 Apr 2026 17:21:49 -0700 [thread overview]
Message-ID: <20260404002149.wtayv6a64vzuppgp@desk> (raw)
In-Reply-To: <CALMp9eTpsenqsWjzmpXLEubn9uNjgZgzgrMwtZ72HDuV_2xgfg@mail.gmail.com>
On Fri, Apr 03, 2026 at 04:39:54PM -0700, Jim Mattson wrote:
> > Since cloud providers have greater control over userspace, the decision to
> > use BHI_DIS_S or not can be left to them. KVM would simply follow what it
> > is asked to do by the userspace.
>
> I feel like we've gone over this before, but if userspace tells KVM
> not to enable BHI_DIS_S, how do we inform Windows that it needs to do
> the longer clearing sequence, despite the fact that the virtual CPU is
> masquerading as Ice Lake?
IMO, if an OS is allergic to a hardware mitigation, and is also aware that
it is virtualized, it should default to a sw mitigation that works everywhere.
> I don't think the virtual mitigation MSRs address that issue.
Virtual mitigation MSRs are meant to inform the VMM about the guest
mitigation. Even if there was a way to tell the guest that it needs to use
a different mitigation, it seems unrealistic for a guest to change its
mitigation post-migration.
next prev parent reply other threads:[~2026-04-04 0:21 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-03 0:30 [PATCH v9 00/10] VMSCAPE optimization for BHI variant Pawan Gupta
2026-04-03 0:30 ` [PATCH v9 01/10] x86/bhi: x86/vmscape: Move LFENCE out of clear_bhb_loop() Pawan Gupta
2026-04-03 15:16 ` Borislav Petkov
2026-04-03 16:45 ` Pawan Gupta
2026-04-03 17:11 ` Borislav Petkov
2026-04-03 0:31 ` [PATCH v9 02/10] x86/bhi: Make clear_bhb_loop() effective on newer CPUs Pawan Gupta
2026-04-03 18:10 ` Jim Mattson
2026-04-03 18:52 ` Pawan Gupta
2026-04-03 20:19 ` Jim Mattson
2026-04-03 21:34 ` Pawan Gupta
2026-04-03 21:59 ` Jim Mattson
2026-04-03 23:16 ` Pawan Gupta
2026-04-03 23:22 ` Jim Mattson
2026-04-03 23:33 ` Pawan Gupta
2026-04-03 23:39 ` Jim Mattson
2026-04-04 0:21 ` Pawan Gupta [this message]
2026-04-04 2:21 ` Jim Mattson
2026-04-04 3:49 ` Pawan Gupta
2026-04-06 14:23 ` Jim Mattson
2026-04-03 0:31 ` [PATCH v9 03/10] x86/bhi: Rename clear_bhb_loop() to clear_bhb_loop_nofence() Pawan Gupta
2026-04-03 0:31 ` [PATCH v9 04/10] x86/vmscape: Rename x86_ibpb_exit_to_user to x86_predictor_flush_exit_to_user Pawan Gupta
2026-04-03 0:31 ` [PATCH v9 05/10] x86/vmscape: Move mitigation selection to a switch() Pawan Gupta
2026-04-03 0:32 ` [PATCH v9 06/10] x86/vmscape: Use write_ibpb() instead of indirect_branch_prediction_barrier() Pawan Gupta
2026-04-03 0:32 ` [PATCH v9 07/10] x86/vmscape: Use static_call() for predictor flush Pawan Gupta
2026-04-03 14:52 ` Sean Christopherson
2026-04-03 16:44 ` Pawan Gupta
2026-04-03 17:26 ` Pawan Gupta
2026-04-03 0:32 ` [PATCH v9 08/10] x86/vmscape: Deploy BHB clearing mitigation Pawan Gupta
2026-04-03 0:32 ` [PATCH v9 09/10] x86/vmscape: Resolve conflict between attack-vectors and vmscape=force Pawan Gupta
2026-04-03 0:33 ` [PATCH v9 10/10] x86/vmscape: Add cmdline vmscape=on to override attack vector controls Pawan Gupta
2026-04-04 15:20 ` [PATCH v9 00/10] VMSCAPE optimization for BHI variant David Laight
2026-04-05 7:23 ` Pawan Gupta
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