From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 918AF3064A3; Mon, 10 Nov 2025 10:37:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762771043; cv=none; b=Ms7uic+kuz+aUb8Qhq4IQ/bF2eCbLBzrkhefgzOuHloyHBw6GQGHYYhvJrOR9mVUBq31oeeMbk/8FEXr+5mGjUyuWO+wspNUPgMKzZClhXYrYhAUU13buUQombmDFmYzvOYJmyRY+GKyeBoCqSe/zM+6BTpiqx+1UOK7GNdCS5A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762771043; c=relaxed/simple; bh=wwdS1VB3vgYSOM1P254K506c5LfSj/vi1RAI9w6ktio=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=E6QjOFoGK5P5mnHc3pCVFeIVNdMktznrVh1SGD+bK1GwtHWLpePYreEh3+6z9quc9WP240SRKkC044/3ohImW2DWgYsh88M/V2zoqoYKzyfYHKGA6isgsJ1eTQ5fZTj562d9TWrB8GAp8q+OtaUfcTGAddaQNug9b/HHXKMvSqM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CEEFE497; Mon, 10 Nov 2025 02:37:12 -0800 (PST) Received: from [10.57.39.147] (unknown [10.57.39.147]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0E4913F66E; Mon, 10 Nov 2025 02:37:12 -0800 (PST) Message-ID: Date: Mon, 10 Nov 2025 11:36:52 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/12] x86/xen: simplify flush_lazy_mmu() To: Ryan Roberts , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , David Hildenbrand , "David S. Miller" , David Woodhouse , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org References: <20251029100909.3381140-1-kevin.brodsky@arm.com> <20251029100909.3381140-3-kevin.brodsky@arm.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 07/11/2025 12:31, Ryan Roberts wrote: > On 29/10/2025 10:08, Kevin Brodsky wrote: >> arch_flush_lazy_mmu_mode() is called when outstanding batched >> pgtable operations must be completed immediately. There should >> however be no need to leave and re-enter lazy MMU completely. The >> only part of that sequence that we really need is xen_mc_flush(); >> call it directly. >> >> Signed-off-by: Kevin Brodsky > This looks functionally equivalent to me, so: > > Reviewed-by: Ryan Roberts > > But I don't think this tidy up is strictly necessary for your series to work? > (perhaps I'll change my mind on that as I go through it). I initially thought it might be, but in the end I think you're right - it should still work fine without this patch. Still, I'd rather avoid unnecessary calls to arch_enter() and arch_leave() as it makes it harder to reason about what is called where. Namely, keeping them here means that a nested call to lazy_mmu_mode_disable() would cause arch_leave() then arch_enter() to be called - rather unexpected. The only calls to arch_enter() and arch_leave() that are left after this series are the ones in and the Xen context-switching logic (the one case where calling arch hooks directly is justified, see discussion on v3 [1]). - Kevin [1] https://lore.kernel.org/all/390e41ae-4b66-40c1-935f-7a1794ba0b71@arm.com/