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 28DC912B71; Wed, 22 Jan 2025 00:22:15 +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=1737505336; cv=none; b=mXRnw7MoJrKr0fVFK8Tk+gXkhybANZXgq/W1cRBBJEo4RNmDOBhcDw/eOa0LyCvM7tjGzX7lKpij/Mgzn7DBu+6owiyIVhnJyaIA1FNtIxWJltTTEyxxZSfp4Kak/LaTC5Bt7td98S5TKy9QhX5mAY1h1KZ+aj1EZ3wha6su2zM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737505336; c=relaxed/simple; bh=/jGFli4cvz5GuKwl53vdKodQbbfB6lqGAT1IVg71WEg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=t6xb0AlHxCL5QW3ZfQOtlZgaCvjSx4j93KZhBGBEhAJHETBXKdAIcvJYop+jbHLxobySvAcSG3DCX1u0+lEgTBrNVMRDoWLikVqRaCAA3D4QrK6DoANtVd/dwnXLXFSZPGY122OlRpXy7FI3bdTKrcqSZCi2Ol6UDzGD1Fys1Mw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m6yz2ru+; 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="m6yz2ru+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1A0ECC4CEDF; Wed, 22 Jan 2025 00:22:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737505335; bh=/jGFli4cvz5GuKwl53vdKodQbbfB6lqGAT1IVg71WEg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=m6yz2ru+LXXh5xzgW1nRGofBLoFG1mOtZGKi5a///oNnHCh2ZlX7+dcv8uCWMxNTP NYc7Ip5HhxveoM1UG1zbALPWHqlghrr9FWkgxzL4ynzknjr2qzRJNXR0bvmmp0LFhV 2OSMqyc+t3WixyaNjJpsZ4FqrFQOpqBUkDbXqnD8oIRzHSRo6BI6S0PtYY51ka7mXT F/aNHCRlDP27nrL0iFxyIILAmTVs3KAxdOxLI4Oy09Y/BLpA3KwnyrjprYZYiv2vA6 /XRCO70HAGc/N4UdSrMWqxSo9SxN0390mZcC3+duriCj1eGd6MeQlfVWwQxOpCa2cX 9AeBV3eiLnmoQ== Date: Wed, 22 Jan 2025 01:22:12 +0100 From: Frederic Weisbecker To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, Juergen Gross , Ajay Kaher , Alexey Makhalov , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. 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Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Subject: Re: [PATCH v4 22/30] context_tracking: Exit CT_STATE_IDLE upon irq/nmi entry Message-ID: References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-23-vschneid@redhat.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250114175143.81438-23-vschneid@redhat.com> Le Tue, Jan 14, 2025 at 06:51:35PM +0100, Valentin Schneider a écrit : > ct_nmi_{enter, exit}() only touches the RCU watching counter and doesn't > modify the actual CT state part context_tracking.state. This means that > upon receiving an IRQ when idle, the CT_STATE_IDLE->CT_STATE_KERNEL > transition only happens in ct_idle_exit(). > > One can note that ct_nmi_enter() can only ever be entered with the CT state > as either CT_STATE_KERNEL or CT_STATE_IDLE, as an IRQ/NMI happenning in the > CT_STATE_USER or CT_STATE_GUEST states will be routed down to ct_user_exit(). Are you sure? An NMI can fire between guest_state_enter_irqoff() and __svm_vcpu_run(). And NMIs interrupting userspace don't call enter_from_user_mode(). In fact they don't call irqentry_enter_from_user_mode() like regular IRQs but irqentry_nmi_enter() instead. Well that's for archs implementing common entry code, I can't speak for the others. Unifying the behaviour between user and idle such that the IRQs/NMIs exit the CT_STATE can be interesting but I fear this may not come for free. You would need to save the old state on IRQ/NMI entry and restore it on exit. Do we really need it? Thanks.