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[70.27.3.10]) by smtp.gmail.com with ESMTPSA id e3-20020ac86703000000b00341a807ed21sm11455951qtp.72.2022.08.16.17.33.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Aug 2022 17:33:30 -0700 (PDT) Date: Tue, 16 Aug 2022 20:33:28 -0400 From: Peter Xu To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: David Hildenbrand , "Dr . David Alan Gilbert" , John Hubbard , Sean Christopherson , Linux MM Mailing List , Andrew Morton , Paolo Bonzini , Andrea Arcangeli , Mike Kravetz Subject: Re: [PATCH v2 1/3] mm/gup: Add FOLL_INTERRUPTIBLE Message-ID: References: <20220721000318.93522-1-peterx@redhat.com> <20220721000318.93522-2-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220721000318.93522-2-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660696413; a=rsa-sha256; cv=none; b=Vhf6loKUzY/46Tzacdg5e2cbarPJF/rIKyWEYe7WBvM24lsh+XG2c6it6Zz0zdif+599V9 r7l4Ja0hYQaHISdq/1lgNbUX6KQ1jKOtZ4UA43aYPS5wkmuJrQexVQOgj2I8LmoTewXzsK ZW5XJeSqy9kuusO0tr4GrPfgK2AwvJM= ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ZnEXm80U; spf=pass (imf09.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660696413; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Gu3f8Uog699HPKySkkdEJkGI/KU5n2mtK1CidLAiQ1I=; b=6K73RAVWM2fwOgq0OMEK1Y9u+BSLfOY9ciVku88tSGDeFQY92yRbwxKXs8taPOsNkoc+UX 4/r92YRaopgsjgG8D/DSNl4q0YWhtxbPpuQ7nKz40ZLBSInli6yzhZ9Xj07edI63MlAmSL XhMGlpAwptAxnKdiP50TrdVroIeXlJk= X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0D749140041 X-Rspam-User: Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ZnEXm80U; spf=pass (imf09.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: bzcskw1hiheeoyax4rxyhfdc44qexa18 X-HE-Tag: 1660696412-122296 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 20, 2022 at 08:03:16PM -0400, Peter Xu wrote: > We have had FAULT_FLAG_INTERRUPTIBLE but it was never applied to GUPs. One > issue with it is that not all GUP paths are able to handle signal delivers > besides SIGKILL. > > That's not ideal for the GUP users who are actually able to handle these > cases, like KVM. > > KVM uses GUP extensively on faulting guest pages, during which we've got > existing infrastructures to retry a page fault at a later time. Allowing > the GUP to be interrupted by generic signals can make KVM related threads > to be more responsive. For examples: > > (1) SIGUSR1: which QEMU/KVM uses to deliver an inter-process IPI, > e.g. when the admin issues a vm_stop QMP command, SIGUSR1 can be > generated to kick the vcpus out of kernel context immediately, > > (2) SIGINT: which can be used with interactive hypervisor users to stop a > virtual machine with Ctrl-C without any delays/hangs, > > (3) SIGTRAP: which grants GDB capability even during page faults that are > stuck for a long time. > > Normally hypervisor will be able to receive these signals properly, but not > if we're stuck in a GUP for a long time for whatever reason. It happens > easily with a stucked postcopy migration when e.g. a network temp failure > happens, then some vcpu threads can hang death waiting for the pages. With > the new FOLL_INTERRUPTIBLE, we can allow GUP users like KVM to selectively > enable the ability to trap these signals. > > Reviewed-by: John Hubbard > Signed-off-by: Peter Xu Will squash the hugetlb support too altogether, which is a one-liner anyway: ---8<--- diff --git a/mm/hugetlb.c b/mm/hugetlb.c index a57e1be41401..4025a305d573 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6176,9 +6176,12 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, fault_flags |= FAULT_FLAG_WRITE; else if (unshare) fault_flags |= FAULT_FLAG_UNSHARE; - if (locked) + if (locked) { fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; + if (flags & FOLL_INTERRUPTIBLE) + fault_flags |= FAULT_FLAG_INTERRUPTIBLE; + } if (flags & FOLL_NOWAIT) fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT; ---8<--- I'll still keep R-b for John and DavidH. Thanks, -- Peter Xu