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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49987b1a31esm211201745e9.2.2026.08.16.03.38.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Aug 2026 03:38:41 -0700 (PDT) From: Stefano Brivio To: Eric Biggers Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Christoph Hellwig , linux-crypto@vger.kernel.org, Herbert Xu , Taehee Yoo , netfilter-devel@vger.kernel.org, Pablo Neira Ayuso , Florian Westphal , Phil Sutter , stable@vger.kernel.org Subject: Re: [PATCH 6/6] netfilter: nft_set_pipapo_avx2: add missing vzeroupper Message-ID: <20260816123839.3670e5c3@elisabeth> In-Reply-To: <20260815205750.169336-7-ebiggers@kernel.org> References: <20260815205750.169336-1-ebiggers@kernel.org> <20260815205750.169336-7-ebiggers@kernel.org> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Sun, 16 Aug 2026 12:38:41 +0200 (CEST) Eric, thanks for taking care of this. The patch looks good to me, I just have two questions: On Sat, 15 Aug 2026 13:57:50 -0700 Eric Biggers wrote: > Since pipapo_get_avx2() uses YMM registers, execute vzeroupper before > returning from it. This is needed to avoid degrading the performance of > any later SSE code that may happen to be executed. Out of curiosity: was this prompted by some observed latency spike in execution of SSE code, or it's just meant to satisfy the recommendation from AMD and Intel to use it while transitioning from AVX to SSE modes? > Fixes: 7400b063969b ("nft_set_pipapo: Introduce AVX2-based lookup implementation") > Cc: stable@vger.kernel.org Is this really stable material? Skipping vzeroupper might have a performance impact, but it's not an issue for correctness. The main reason why I'm asking is that, while vzeroupper might look harmless and obviously safe, it actually caused CVE-2023-20593 ("ZenBleed") on AMD Zen 2. I expect systems receiving stable kernel updates to also run the patched microcode by now, so I'm not overly concerned in any case. -- Stefano