From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5ECC7C388F7 for ; Sun, 25 Oct 2020 10:05:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1508C222B9 for ; Sun, 25 Oct 2020 10:05:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603620346; bh=Yz7CUN4MWFZyCixuGZFuoyPNNqXyaUN69UEhyNH2HD0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=tfiVu7iYr6xBitMT0j852TAZv/Me7qU3ZjOxuOiyQC0PXnc+eK6umNv0mH1Cx5jau gjUHGvWnNaVL3O9lDve32i3YyNLUe50R7zk/09Y2HhMcf1BnWgCh7kOD0RS0QSMhpX lCZ0GouVRbWqHizsn47wYgnrRl59OuaIMPIAZY4E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1415052AbgJYKFo (ORCPT ); Sun, 25 Oct 2020 06:05:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:50830 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1415044AbgJYKFo (ORCPT ); Sun, 25 Oct 2020 06:05:44 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CB9D320936; Sun, 25 Oct 2020 10:05:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603620343; bh=Yz7CUN4MWFZyCixuGZFuoyPNNqXyaUN69UEhyNH2HD0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dY870apAuSGY/RCogszpF34aybCKtDEm80V+RX4x+lW3TQSebvLX2aFmR2X8zc0/I YMredqBWBcB3hQL3Y4AlI3GvNEV1nojrFo1NZKZpScN7nHQHlCe684MVpldc7HK8o7 UrHfLnQtylWAkAzQ2OanJNzkpE+bVWQs0ECdw7zI= Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kWcuD-00424D-VO; Sun, 25 Oct 2020 10:05:42 +0000 Date: Sun, 25 Oct 2020 10:05:41 +0000 Message-ID: <87zh4aoc22.wl-maz@kernel.org> From: Marc Zyngier To: Gavin Shan Cc: kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, will@kernel.org, alexandru.elisei@arm.com Subject: Re: [PATCH 2/3] KVM: arm64: Don't map PUD huge page if it's not available In-Reply-To: <20201025002739.5804-3-gshan@redhat.com> References: <20201025002739.5804-1-gshan@redhat.com> <20201025002739.5804-3-gshan@redhat.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 EasyPG/1.0.0 Emacs/26.3 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: gshan@redhat.com, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, will@kernel.org, alexandru.elisei@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 25 Oct 2020 01:27:38 +0100, Gavin Shan wrote: > > PUD huge page isn't available when CONFIG_ARM64_4K_PAGES is disabled. > In this case, we needn't try to map the memory through PUD huge pages > to save some CPU cycles in the hot path. > > This also corrects the code style issue, which was introduced by > commit <523b3999e5f6> ("KVM: arm64: Try PMD block mappings if PUD mappings > are not supported"). > > Signed-off-by: Gavin Shan > --- > arch/arm64/kvm/mmu.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index a816cb8e619b..0f51585adc04 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -787,9 +787,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > vma_shift = PAGE_SHIFT; > } > > +#ifdef CONFIG_ARM64_4K_PAGES > if (vma_shift == PUD_SHIFT && > !fault_supports_stage2_huge_mapping(memslot, hva, PUD_SIZE)) > - vma_shift = PMD_SHIFT; > + vma_shift = PMD_SHIFT; > +#endif > > if (vma_shift == PMD_SHIFT && > !fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) { I really don't buy the "CPU cycles" argument here either. Can you actually measure any difference here? You have taken a fault, gone through a full guest exit, triaged it, and are about to into a page mapping operation which may result in a TLBI, and reenter the guest. It only happen a handful of times per page over the lifetime of the guest unless you start swapping. Hot path? I don't think so. M. -- Without deviation from the norm, progress is not possible.