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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 96ED0C4450A for ; Fri, 10 Jul 2026 22:12:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 656386B00CC; Fri, 10 Jul 2026 18:12:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6073E6B00CF; Fri, 10 Jul 2026 18:12:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 51EE76B00D0; Fri, 10 Jul 2026 18:12:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 277656B00CC for ; Fri, 10 Jul 2026 18:12:21 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id A6BA6405C5 for ; Fri, 10 Jul 2026 22:12:20 +0000 (UTC) X-FDA: 84974266440.09.CCC32DF Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf28.hostedemail.com (Postfix) with ESMTP id F154CC000B for ; Fri, 10 Jul 2026 22:12:18 +0000 (UTC) Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="vrKNqD/R"; spf=pass (imf28.hostedemail.com: domain of akpm@linux-foundation.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783721539; b=g8qNqUUe4T+BcnxBKBNPTPenkcEwNEPN4q1nSLB9zV0OIUJPNdPQ2sCMLQBnIVSJbVJmo5 eklOHZrjczFaG5Npho0ZSku7ZbcTRJUGqJZ1Y5X28lcrVvev9a11TN8gtBhMfwYytLgdFH NqNBm22gcSMpZEjmYiSF8jrydNQ6NjI= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b="vrKNqD/R"; spf=pass (imf28.hostedemail.com: domain of akpm@linux-foundation.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783721539; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=vZPCZ7vPd1NuY/NOvoRK1wg4DzJ9OfLHTV03rmwvPpc=; b=Mw6MfqGDBi5EDjPGOzoiMHsR5jCzi6+v/I/U3SSfRKuTnk+q8An9ZqCKHDgAHCw2pGRA0S GKqJ/DghzDSm2ciHc0JPFmuwiOVquvpTrvkB8vwuzVRm4oXs6SRVFppHangCiLFoj0ghnq w8Rb1wLWnIDNcHeLvckmrW+hVN4IKm4= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 15A9C41A63; Fri, 10 Jul 2026 22:12:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C384A1F00A3E; Fri, 10 Jul 2026 22:12:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783721538; bh=vZPCZ7vPd1NuY/NOvoRK1wg4DzJ9OfLHTV03rmwvPpc=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=vrKNqD/RSYZafjQOwVndW01m5aLwswfnuVAfqI5wWJJiUGxMunb7KBRBbR+vIavWm Jwjm7GTEqUP54kAGt2vK1og8+S0X4K5USi4sGzpjMkFtbq+y8rgsLvuLfwWeKzYqds EILDdi2jW5IYL94/XhZxUobGPOo9gvao6LZmzPYg= Date: Fri, 10 Jul 2026 15:12:16 -0700 From: Andrew Morton To: Stanislav Kinsburskii Cc: airlied@gmail.com, akhilesh@ee.iitb.ac.in, corbet@lwn.net, dakr@kernel.org, david@kernel.org, decui@microsoft.com, haiyangz@microsoft.com, jgg@ziepe.ca, kees@kernel.org, kys@microsoft.com, leon@kernel.org, liam@infradead.org, lizhi.hou@amd.com, ljs@kernel.org, longli@microsoft.com, lyude@redhat.com, maarten.lankhorst@linux.intel.com, mamin506@gmail.com, mhocko@suse.com, mripard@kernel.org, nouveau@lists.freedesktop.org, ogabbay@kernel.org, oleg@redhat.com, rppt@kernel.org, shuah@kernel.org, simona@ffwll.ch, skhan@linuxfoundation.org, surenb@google.com, tzimmermann@suse.de, vbabka@kernel.org, wei.liu@kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rdma@vger.kernel.org Subject: Re: [PATCH v8 4/8] mshv: Use hmm_range_fault_unlocked_timeout() for region faults Message-Id: <20260710151216.0397a6f9ac5c7b4ccd274cc1@linux-foundation.org> In-Reply-To: <178371881034.900500.5214601525971121683.stgit@skinsburskii> References: <178371866223.900500.12312667138651735591.stgit@skinsburskii> <178371881034.900500.5214601525971121683.stgit@skinsburskii> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: F154CC000B X-Stat-Signature: f155d6sxhf8aa66n1aztcspw1o417ouh X-HE-Tag: 1783721538-156165 X-HE-Meta: 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 kFVCV6RV Py2zWCMD1A0wdMacNFEGmVR5OrN89UkZSTrvp6e9Y1SV0di1/AyD2IhQm0UQuJAIpomakbSjgfv4gPrjoYB2qY6NyYI0cUozLGZFtHnfC8rR7NcQ2ehGlRtOUbjcW9sl01DE7+s4hC5xkkL+L6lDPWZmU3rwHaXzkttlQYn7FS4S+C9LZnWF74MILdLiKDr2I6y676VLAGTgBJuqK9sqeiKsVwLlZa3d9f3lzIHDdpk6wDfO+lt5Yce/iMLytrgWb0LyTFeZPCMrStdhR6iZw1+hh9YueThOBdOMwyGOpea47JRENdObLp7mDUzAvLFTEmOya Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 10 Jul 2026 14:26:50 -0700 Stanislav Kinsburskii wrote: > MSHV currently faults movable memory regions by taking mmap_read_lock() > around hmm_range_fault(). That prevents the fault path from handling VMAs > whose fault handlers need to drop mmap_lock, such as userfaultfd-backed > mappings. > > Use hmm_range_fault_unlocked_timeout() instead. Passing a timeout of 0 > preserves MSHV's existing unbounded retry behavior while letting the HMM > helper own mmap_lock acquisition and refresh range->notifier_seq internally > before walking the range. After the fault succeeds, MSHV still takes > mreg_mutex and checks mmu_interval_read_retry() before installing the pages > into the region, so the existing invalidation synchronization is preserved. > > Fold the small fault-and-lock helper into mshv_region_range_fault(), since > the remaining retry path is just the standard "fault, take the driver lock, > check the interval notifier sequence" pattern. > > ... > > @@ -452,13 +412,19 @@ static int mshv_region_range_fault(struct mshv_mem_region *region, > range.start = region->start_uaddr + page_offset * HV_HYP_PAGE_SIZE; > range.end = range.start + page_count * HV_HYP_PAGE_SIZE; > > - do { > - ret = mshv_region_hmm_fault_and_lock(region, &range); > - } while (ret == -EBUSY); > - > +again: > + ret = hmm_range_fault_unlocked_timeout(&range, 0); > if (ret) > goto out; > > + mutex_lock(®ion->mreg_mutex); > + > + if (mmu_interval_read_retry(range.notifier, range.notifier_seq)) { > + mutex_unlock(®ion->mreg_mutex); > + cond_resched(); > + goto again; > + } > + If the calling process has realtime scheduling policy and either a) we're uniprocessor or b) this process and the holder of interval_sub->invalidate_seq are both pinned to the same CPU then cond_resched() won't do anything, and this might be an infinite loop?