From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=113.46.200.224 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793340116; b=J9xMRm4s497Gn0a6kJvJo4MblRlzON3Yx2lK8+YnsNgS2ZVA8nr/bpOm4qN5SuiD0pUd SGjWuneqornIYs6tiUkLTEEeACC3rM7LdClYB57kNX54N0FLDQTvkLFDmrzlaGvfD2cwQ zrk4iV7f26txsXbhUSe3nh+8u5clTtpAXi3AhMeF51cj40HcptTMFRAVH/r24S+4pGuqq 0PKxcjfoGlKRMkNNWdPsrrp0CX3R8jlAAd7kglrl92DAljaH67+7pXWRyQ6wLWbzIqSW3 3DGwnfm24cc35SeWjHBBTFqaxcORqOXHpik/yVDdHLpwKJJyJJal+kfx3IL46A257wA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793340116; h=DMARC-Filter:dkim-signature:Received:Received:Received:Message-ID: Date:MIME-Version:User-Agent:Subject:To:CC:References:From: In-Reply-To:Content-Type:Content-Transfer-Encoding:X-Originating-IP: X-ClientProxiedBy; bh=QV64RGtqfAWvcrVEQ/J8fVuvfalRZ9xgiHmT8AuAPYU=; b=Fq9CBlMVL1XbFcouOO/mAX474ph5JYO1HiFhOJjBngne9hkyEz6QZav6WHhCqJav0a+E viFOtKgCAwfmPAjJ1JpmtVZEREBZeuh2ba8wtL25Ox5GxNKFrALILuWAxUXbkb9M2cFoB uVdE3+zTvt9BvzwoaXmXp6d4Z27P6f7WuEEA4JoIUQOSdS6eNg6jeNa5GXKh054P+n0aq FBcxWBs2qUKEZgGbeluAXqi8tBEvHeDwxsglfYX+S5b9gLdRYkDsr9iYwDkra/bdoSmqg +ROBqq1KEcrxRuJQOJ7cX9R8GpIE782jupWZOR/HS0SaoFI2fQsG+K6GfyHOhAy5WLg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass header.d=huawei.com header.i=@huawei.com header.a=rsa-sha256 header.s=dkim header.b=WrESf68H; arc=none smtp.remote-ip=113.46.200.224 Received: from canpmsgout09.his.huawei.com (canpmsgout09.his.huawei.com [113.46.200.224]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1A5E9606A330 for ; Fri, 30 Oct 2026 06:01:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 1A5E9606A330 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=huawei.com header.i=@huawei.com header.a=rsa-sha256 header.s=dkim header.b=WrESf68H dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=QV64RGtqfAWvcrVEQ/J8fVuvfalRZ9xgiHmT8AuAPYU=; b=WrESf68Hs0YRccK+XTYqrJfLNsgVzD1tFRK4UfgJfK6v9eiCHydujqzBqR/Bwks32HSm99JSJ yvt1zNYgJBR5nwE/R2ciu1QBW/2WrpfgPrq3hPiw3I9XbIs1YCBbapoRe4nlDW26KEOxSrwn3Pt DdlrRNDetKULhgh6Sk4aBhw= Received: from mail.maildlp.com (unknown [172.19.163.200]) by canpmsgout09.his.huawei.com (SkyGuard) with ESMTPS id 4jG9Tg2GvTz1cySS; Fri, 30 Oct 2026 14:01:43 +0800 (CST) Received: from kwepemr100010.china.huawei.com (unknown [7.202.195.125]) by mail.maildlp.com (Postfix) with ESMTPS id 3C4D840563; Fri, 30 Oct 2026 14:01:51 +0800 (CST) Received: from [10.67.120.103] (10.67.120.103) by kwepemr100010.china.huawei.com (7.202.195.125) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Fri, 30 Oct 2026 14:01:50 +0800 Message-ID: Date: Fri, 30 Oct 2026 14:01:49 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 5/5] KVM: arm64: Enable HAFDBS for guests not on migration To: Leonardo Bras CC: liuyonglong , Oliver Upton , Marc Zyngier , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Mark Rutland , Raghavendra Rao Ananta , , , , Zhou Wang References: <3e464bef-8dfe-44a3-afea-3c276ae87cd8@huawei.com> <8eaaba87-7881-49c4-a76a-51dec2f29ffc@huawei.com> <52945586-8c5c-4991-bd92-fe02aaf79fbe@huawei.com> From: Tian Zheng In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: kwepems200002.china.huawei.com (7.221.188.68) To kwepemr100010.china.huawei.com (7.202.195.125) On 10/29/2026 7:54 PM, Leonardo Bras wrote: > On Thu, Oct 29, 2026 at 10:54:24AM +0800, Tian Zheng wrote: >> Hi Leo, >> >> I've read your discussion with Oliver on DBM RFC v2. As a suggestion, >> maybe we should go with Oliver's approach, i.e. revert to the v1 scheme >> and continue fixing from there. > > Hi Tian, > I have been reading a bit more about permission indirection to try figuring > out a way that the change may work for both ways. > > The problem with the previous approach is that it assume DBM=write at all > times, which is not architecturally correct. Having DBM=write only on > HAFDBS=on as suggested would require us to transverse the whole pagetable > to convert encodings when we enable/disable it, which can be quite > expensive. > > One option would be to always enable HAFDBS when system supports HDBSS, but > I still have to figure out if that causes any performance regression before > suggesting. > > The option I am pursuing is thinking on an unified code path for direct > permissison (both HACDBS=on and HACDBS=off) so we don't have to convert > between them, neither worry about the impact of HAFDBS=on on performance. > > I will reply on the thread once I figure one of those options out. > > Thanks! > Leo Hi Leo, Sounds good. I'll wait for your next version and review it once it's posted. Thanks, Tian