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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BBFAACAC58E for ; Thu, 11 Sep 2025 18:57:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Q4SQGKIlkipINvl+R90RuJAQdt11TIrJOgV4rbHAwlI=; b=Y11AY7FlsAppyGOKEavThHhX9Q XlWMqOYgf+y2vgTrlpFbBXM/ZFcIGyWXKse9wwEZFdWeyCUJ5Pii8/OTZdulzXyS+ImvDdpGVc3SF TKq0pLCX7oCcU0lxs5LPtGfyc9UoqU1mq8KOLF4z3GT+EcgvwqYKLtj5IuD2W4GaIRUD6AFPTx21i uma5WGzBd0izBLwXL+ls5sMS/BLS/c6f5vZ68vywDxFS4hbOyieR40s/Fgw1BQLhCCtPXkmtGF+V0 LdwzR22bnNjaDvGU3+rpgb4LE76/Bt70DDCXPApgAZ85ljDULK3RCkuYEU3KQKEmsXo3SoGHxYDSR Wor5O48A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwmUR-00000004s5s-1vuP; Thu, 11 Sep 2025 18:57:51 +0000 Received: from out-170.mta1.migadu.com ([2001:41d0:203:375::aa]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwmUO-00000004s3i-0CdW for linux-arm-kernel@lists.infradead.org; Thu, 11 Sep 2025 18:57:50 +0000 Date: Thu, 11 Sep 2025 11:56:43 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1757617064; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Q4SQGKIlkipINvl+R90RuJAQdt11TIrJOgV4rbHAwlI=; b=I6QD9dGiUYM3bhHavuuokGgkfn2aw33ufD+qMrk74tUf/3fweSDpi4SADE59D35WlSLTsw acyEHKnhvh93iLBKEofeNyCplFpeBZ4i3N4UtjriguIONPSw6IPT6s6YHc0Hn7OrFw/61y nkVQuprWrsyVpLiuisZxOC4R9ithJcY= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Jack Thomson Cc: maz@kernel.org, pbonzini@redhat.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, isaku.yamahata@intel.com, roypat@amazon.co.uk, kalyazin@amazon.co.uk, jackabt@amazon.com Subject: Re: [PATCH 0/6] KVM ARM64 pre_fault_memory Message-ID: References: <20250911134648.58945-1-jackabt.amazon@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250911134648.58945-1-jackabt.amazon@gmail.com> X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250911_115748_741852_A0DF10A4 X-CRM114-Status: GOOD ( 12.89 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Jack, On Thu, Sep 11, 2025 at 02:46:42PM +0100, Jack Thomson wrote: > From: Jack Thomson > > Overview: > > This patch series adds ARM64 support for the KVM_PRE_FAULT_MEMORY > feature, which was previously only available on x86 [1]. This allows > a reduction in the number of stage-2 faults during execution. This is > beneficial in post-copy migration scenarios, particularly in memory > intensive applications, where high latencies are experienced due to > the stage-2 faults when pre-populating memory via UFFD / memcpy. Thanks for posting the series. More of a general comment on the UAPI documentation: "... However, KVM does not mark any newly created stage-2 PTE as Accessed." This behavior is x86-specific since kvm_pgtable_stage2_map() will lay down PTEs with the AF set. Probably shouldn't have documented the internal state of the stage-2 in the first place but oh well, please just update the UAPI description to make it clear this is x86-specific. Thanks Oliver