From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 85C2414EC73; Sun, 22 Feb 2026 21:34:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771796070; cv=none; b=sQYUOqorpg6PdfpIERBzTU647XMMy8LDXC5znKDDcxKJ67umxC/jSAmqvGbO73E7UgAZ16xeZUz4Z0sUch7893fVBCRD9ARtos2pkZe2KUPzjV7JG12Ne/QWjREBanv4kw/XHcgAsXGm+bng04JsDviEKvzJ8VrntsMgZ0VzlK4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771796070; c=relaxed/simple; bh=MoM4gAfGlJ1ngKCroMgt6s8hQQRUOv2GP6lsvWBTYTk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=VYGCdeAwCHH9NFzgn1qL0deKb5V2bt1QnvnLM89HwIZqSB21gNnNLmNFFRRov5gHxJHJUoF6AMrkaIQiEhmGCcgueYbKIiRj/LfNjujvghy967I4AYAuhzU+NPApSw3Owyu7j3vlDarhvJdRTp0ktBSUb2VleM4xM3OcdihlWl0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=F3kE5G5Y; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="F3kE5G5Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3118FC116D0; Sun, 22 Feb 2026 21:34:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771796070; bh=MoM4gAfGlJ1ngKCroMgt6s8hQQRUOv2GP6lsvWBTYTk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=F3kE5G5YSHiCVZ5mOwWBQ1EmkdZUUxri8FWvUUe1+bPk6Car0R0kut2uvNuYHVkAa g8IvAYcI7E8/6hHCb/jrPziQTKClMwrJ6H0Y/aYHLJyimbtr/frfU8CLViovCDA9UV HIObLbqEucr9FrLIbWX5/hRoPhPnR0+zxQyrVmCTdNaMIGloFGLnnqKAP5W6Ewm6w7 I/owa0GiWqAQBaI4TmPdDfE67f10RHZ+BDAgtt/1JTGJALkdfXpJeUzGxFHrjR/KHe NiTE6uiB4kCm6q8SZrGgK2AZmAXo4GAErDwos4utQpdh9gKlK0o0vXjumdP0UVYmSi KhiPc2AZqyPxQ== From: Thomas Gleixner To: Ryan Roberts , Catalin Marinas , Will Deacon , Huacai Chen , Madhavan Srinivasan , Michael Ellerman , Paul Walmsley , Palmer Dabbelt , Albert Ou , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Ingo Molnar , Borislav Petkov , Dave Hansen , Kees Cook , "Gustavo A. R. Silva" , Arnd Bergmann , Mark Rutland , "Jason A. Donenfeld" , Ard Biesheuvel , Jeremy Linton , David Laight Cc: Ryan Roberts , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v4 3/3] randomize_kstack: Unify random source across arches In-Reply-To: <20260119130122.1283821-4-ryan.roberts@arm.com> References: <20260119130122.1283821-1-ryan.roberts@arm.com> <20260119130122.1283821-4-ryan.roberts@arm.com> Date: Sun, 22 Feb 2026 22:34:26 +0100 Message-ID: <87ecmcwjh9.ffs@tglx> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Mon, Jan 19 2026 at 13:01, Ryan Roberts wrote: > I tested an earlier version of this change on x86 bare metal and it > showed a smaller but still significant improvement. The bare metal > system wasn't available this time around so testing was done in a VM > instance. I'm guessing the cost of rdtsc is higher for VMs. No it's not, unless the hypervisor traps RDTSC, which would be insane as that would cause massive regressions all over the place. So guessing is not really helpful if you want to argue performance. Thanks, tglx