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AJvYcCUUWUTy7opuryuqCqmtZ+mVTprgBzedG01utDeOZEDJEGlCmuFzsXX+FxB50BqQyFSVTuQ0d6fJLw==@kvack.org X-Gm-Message-State: AOJu0Yxm+ht70pm/EuFgrGHjNKMZkKzrHh7PgAgmzJElj4TPybfbxLeN xSjp1HXWvvssmxVED8/E/LrFIpMB4OwAwpKQaVGCYHTx90VOLmF73xKJGdKYotaQhDce1ppHgf/ NbaMYVA== X-Google-Smtp-Source: AGHT+IG9Zd3t+86XRNhfr6MOl3z2x5n36Sr6uReq0nGSm2P7jNviBzkfzWGC0x9bWFlsxNGdGfsNX6JxluA= X-Received: from pjuj14.prod.google.com ([2002:a17:90a:d00e:b0:32b:95bb:dbc]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3ec5:b0:327:e018:204a with SMTP id 98e67ed59e1d1-33b50f85081mr35201870a91.0.1760468794156; Tue, 14 Oct 2025 12:06:34 -0700 (PDT) Date: Tue, 14 Oct 2025 12:06:32 -0700 In-Reply-To: Mime-Version: 1.0 References: <20251010153839.151763-1-vschneid@redhat.com> <20251010153839.151763-20-vschneid@redhat.com> Message-ID: Subject: Re: [PATCH v6 19/29] KVM: VMX: Mark vmx_l1d_should flush and vmx_l1d_flush_cond keys as allowed in .noinstr From: Sean Christopherson To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Josh Poimboeuf , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnaldo Carvalho de Melo , Paolo Bonzini , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Sami Tolvanen , "David S. Miller" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Mel Gorman , Andrew Morton , Masahiro Yamada , Han Shen , Rik van Riel , Jann Horn , Dan Carpenter , Oleg Nesterov , Juri Lelli , Clark Williams , Yair Podemsky , Marcelo Tosatti , Daniel Wagner , Petr Tesarik Content-Type: text/plain; charset="us-ascii" X-Stat-Signature: xqx9k6yhfcioxydjtpbcbd74o18j7pin X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 84DAF14000C X-HE-Tag: 1760468795-955696 X-HE-Meta: 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 lRqxfYKL 8rDEM3mQmmWeEGH30gA391NxN530X/z4wQ6cEhnxHgz7HKONK6dC11ogN/ba52weYDH1HbFOtOJxY8nILMzLk+q+vxoXHEVkD6MdtP8gYaBPjHM9V3TpyguoNO3qLE5g2cB7plkWvQwLT2fbrhqnqG8FHk8fcxgldpoZEA2pOoj0oTeXT0TPd38DARC8LfKrTeymtTlvXuCjcyxrt/1qBekn4pn55i4DsouuvaassPPsXlM7C+mDyXoSUeLw08rl2KldImpg0F726Aq7ttyTN8VPmt6UYGV93Fax732NCJgnWWDq9YNdkcpAGHsHXltzPzuNuNoF0pUQg/D9aJPtE7Z9pQJRqiinykOnIUXNDnlFtZyLzkyBXNEjR+nqFfhoobr1wq95c+dPlUNCMu9gLrA0xet9vDakAl3hyeXY2PSHyyQyWoYusjRu3P0m2uTCHNJTfKb7Yf5krpLZZytv6UAnCPPpU4qPX90+48sSMmpi6xscSb5Xf5FgAzZ9axCHEdxOK885D76XyRHR2mf/LMYNjT1LxE3gLx0KZVhxW06dg6Ymvh/hlPo++vQ/bfTDrRaeVzmRyfCfsXog0vQqFlHRgoOXQ8/a5OHJ3QRLsOA7OGanccx6cK8CyH8Z4mBETiPmD8/gZ+bwXVgNCitkuTM6n+BaNxsWEF5Bd8p+41foMb0n5Fqd+LhHnKR7oc6Uk0RS9 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Oct 14, 2025, Valentin Schneider wrote: > On 13/10/25 17:01, Sean Christopherson wrote: > > On Fri, Oct 10, 2025, Valentin Schneider wrote: > >> Later commits will cause objtool to warn about static keys being used in > >> .noinstr sections in order to safely defer instruction patching IPIs > >> targeted at NOHZ_FULL CPUs. > >> > >> These keys are used in .noinstr code, and can be modified at runtime > >> (/proc/kernel/vmx* write). However it is not expected that they will be > >> flipped during latency-sensitive operations, and thus shouldn't be a source > >> of interference wrt the text patching IPI. > >> > >> Mark it to let objtool know not to warn about it. > > > > Can you elaborate in the changelog on what will happen if the key is toggle? > > IIUC, smp_text_poke_batch_finish() will force IPIs if noinstr code is being > > patched. > > Right! > > > Even just a small footnote like this: > > > > Note, smp_text_poke_batch_finish() never defers IPIs if noinstr code is > > being patched, i.e. this is purely about silencing objtool warnings. > > > > to make it clear that there's no bug/race being introduced. > > Good point. How about: > > """ > Later commits will cause objtool to warn about static keys being used in > .noinstr sections in order to safely defer instruction patching IPIs > targeted at NOHZ_FULL CPUs. > > The VMX keys are used in .noinstr code, and can be modified at runtime > (/proc/kernel/vmx* write). However it is not expected that they will be > flipped during latency-sensitive operations, and thus shouldn't be a source > of interference for NOHZ_FULL CPUs wrt the text patching IPI. > > Note, smp_text_poke_batch_finish() never defers IPIs if noinstr code is > being patched, i.e. this is purely to tell objtool we're okay with updates > to that key causing IPIs and to silence the associated objtool warning. > """ LGTM. With the updated changelog, Acked-by: Sean Christopherson