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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 72FD6C3A589 for ; Thu, 15 Aug 2019 17:18:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 488EB205F4 for ; Thu, 15 Aug 2019 17:18:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="tjAQYIIr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731354AbfHORSn (ORCPT ); Thu, 15 Aug 2019 13:18:43 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:36496 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731134AbfHORSn (ORCPT ); Thu, 15 Aug 2019 13:18:43 -0400 Received: by mail-pf1-f194.google.com with SMTP id w2so1649299pfi.3; Thu, 15 Aug 2019 10:18:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=O0iU9h/CgsDkbZj91TD8RQDyFQ2IpZ1Yt3QLDe5vqPg=; b=tjAQYIIro/DnauaXI3INnjRJ/TkqSKPI5VSGVznvGeeUcH0xKxwESp9IFecKpept4y +TKAvO8LFDVo2JSUms7f4AHRLykJ3aWjv//YwbFmTCtpmd1PuO44oXTGx27ZPYbp0tCG VHFtbXKcpvCkHkhJ7FmwnWvPHbRKal59zAKDeiIEh51J2Se0/B2fYl1qdhPdYKC+nNtC t+USv/D8HJg3gS+E2b1TsBmCsghRIleh5YAorwhmjPW5URMuroF8cwyorpGyHFwaQPxA 9YlgiSCiQOgTwIpD5QzJNmHSKLV1u0SinXcon/R22PEBoOuozKKr1wutxKfgWL+EU/rE i42Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=O0iU9h/CgsDkbZj91TD8RQDyFQ2IpZ1Yt3QLDe5vqPg=; b=T5Fkv0tpFHdJkCOpmCZ78/6wCSoAsPtmrpQKqGUYjAiTgiN01Q696Opanv6K0kZbjp wiwDijmkmx72DDK4TJTFmSptsyzkuJGTZbyjccob/347YdySBVSnnNTs4lScY7PHeqz+ kYX95MfYrkOwF29MuXIpyjpWgYr4IeF1Boj955fW+y+c2J9II2CvcDUGWm2M5JUPUJSc 8fzN9ibumj664GhaIFYUtElXzu4BbIw59S+hFL65sm6CEy/Zm6idvthRzamCJ5+526sW afmRgTr3B/6FtryKFVNX6GkI3h7ogW14jjJyLGKPrrbcPM7PumYzA1xlfPWdqA4gZviO fGFw== X-Gm-Message-State: APjAAAWpxTQU13exDpQBa62DzSTwEC7roJ+op0+1zI9MxFxszHP/wCL3 tkiSbwqyQJvOF+yEke9jX+c= X-Google-Smtp-Source: APXvYqy7W7kXMKmt5qV1vz6zH8QBZDpT0zmtLNiJOWrKRdx4CqeHfrqqlOkAd7IoFjwEYuU4TVZlEA== X-Received: by 2002:aa7:8f2e:: with SMTP id y14mr6509394pfr.113.1565889522309; Thu, 15 Aug 2019 10:18:42 -0700 (PDT) Received: from bharath12345-Inspiron-5559 ([103.110.42.34]) by smtp.gmail.com with ESMTPSA id d129sm3343983pfc.168.2019.08.15.10.18.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Aug 2019 10:18:41 -0700 (PDT) Date: Thu, 15 Aug 2019 22:48:35 +0530 From: Bharath Vedartham To: Paolo Bonzini Cc: rkrcmar@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, khalid.aziz@oracle.com Subject: Re: [Question-kvm] Can hva_to_pfn_fast be executed in interrupt context? Message-ID: <20190815171834.GA14342@bharath12345-Inspiron-5559> References: <20190813191435.GB10228@bharath12345-Inspiron-5559> <54182261-88a4-9970-1c3c-8402e130dcda@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54182261-88a4-9970-1c3c-8402e130dcda@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Aug 13, 2019 at 10:17:09PM +0200, Paolo Bonzini wrote: > On 13/08/19 21:14, Bharath Vedartham wrote: > > Hi all, > > > > I was looking at the function hva_to_pfn_fast(in virt/kvm/kvm_main) which is > > executed in an atomic context(even in non-atomic context, since > > hva_to_pfn_fast is much faster than hva_to_pfn_slow). > > > > My question is can this be executed in an interrupt context? > > No, it cannot for the reason you mention below. > > Paolo hmm.. Well I expected the answer to be kvm specific. Because I observed a similar use-case for a driver (sgi-gru) where we want to retrive the physical address of a virtual address. This was done in atomic and non-atomic context similar to hva_to_pfn_fast and hva_to_pfn_slow. __get_user_pages_fast(for atomic case) would not work as the driver could execute in interrupt context. The driver manually walked the page tables to handle this issue. Since kvm is a widely used piece of code, I asked this question to know how kvm handled this issue. Thank you for your time. Thank you Bharath > > The motivation for this question is that in an interrupt context, we cannot > > assume "current" to be the task_struct of the process of interest. > > __get_user_pages_fast assume current->mm when walking the process page > > tables. > > > > So if this function hva_to_pfn_fast can be executed in an > > interrupt context, it would not be safe to retrive the pfn with > > __get_user_pages_fast. > > > > Thoughts on this? > > > > Thank you > > Bharath > > >