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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 57E9EC04E69 for ; Tue, 25 Jul 2023 16:04:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231936AbjGYQE0 (ORCPT ); Tue, 25 Jul 2023 12:04:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229623AbjGYQEP (ORCPT ); Tue, 25 Jul 2023 12:04:15 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01B3F2126 for ; Tue, 25 Jul 2023 09:04:02 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-573d70da2afso71964397b3.2 for ; Tue, 25 Jul 2023 09:04:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1690301041; x=1690905841; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=JzfMU5Qs8JliFSPK4e1C5em4CWxZCGfzp6e2iymS9Yg=; b=dW59zwmrsLAamcGnirE6A1LfKT51T61DtWDAOhx4/cSvK3sOAiDmr+BlK4XiPthtzP CN9MlQi3HhBVcH71uuUqq+M14CfwGnGPEE/BpfevOBdEFKHG7J0iaICViLaRAky8BhEp HFcQ65KDccgqhPQn/ChYInnlcEfq7qr0Ma/Jgkr7SmWI+05vO/bEbUCWl8Rn7I2emovI UeVOyMZohBruEuz8fBipp3NgVzf/qbnB/hnqT0XX1CDCZ3KOl7DJQE2yXx50QpLL6+Az IlluRAj7yyIarMAgzXmFlQrKZdiqjqFyPfBBVM/tbJmItA4hkVu10uPsnU/tUYfyPMpN N63Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1690301041; x=1690905841; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=JzfMU5Qs8JliFSPK4e1C5em4CWxZCGfzp6e2iymS9Yg=; b=YW85mWXldzB8pofJOpPKhV//T+eVxFJdWrLBCyY+XXmcN+kCfnOFVq6g5wdOPxSLge YI19NNa+FnRx9pjX2cpERMfmDyT2quqt0fD/U9YB7egphd6oIjV8/a00SGqzBgDj+k8a cjd6/MWFyGL+b+Gb4Ow6+aJ/cWfY0egHedEE1GVw6YHhPIvRS9+DiBZ+ppLkVkKkfhMA i0nQEAsS5GeFdn10eHEAu11fOlq0vCqECqvB/H+it62wTw/gDZANSTV4+hYVo7YZMhFm Mulum2J1GkQ3G7sOu+ntiHmCnPN4Je72N2UqQuP6qt7EMJ0F9LnXZWVAajSvkFDat1o8 bMVA== X-Gm-Message-State: ABy/qLY1JLKytx6NsDTa3Ct6CyuyAWp5IQfM95A4IR4ULlrmamg6DADU KCeGyvRvThAuWVBeY9AaYs1VOJXCoso= X-Google-Smtp-Source: APBJJlH1niyzp4cjBeRls9BsaNe03YLK4iKuUQJEO3t7N9JW3OW9U+d5kcfXqA22KUPE/pwVy1vkIiRVphQ= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:46d4:0:b0:cf9:3564:33cc with SMTP id t203-20020a2546d4000000b00cf9356433ccmr81585yba.13.1690301041144; Tue, 25 Jul 2023 09:04:01 -0700 (PDT) Date: Tue, 25 Jul 2023 09:03:59 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230718234512.1690985-1-seanjc@google.com> <20230718234512.1690985-13-seanjc@google.com> Message-ID: Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory From: Sean Christopherson To: Wei W Wang Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , "Matthew Wilcox (Oracle)" , Andrew Morton , Paul Moore , James Morris , "Serge E. Hallyn" , "kvm@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "linux-mips@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "kvm-riscv@lists.infradead.org" , "linux-riscv@lists.infradead.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-security-module@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Yu Zhang , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , Vlastimil Babka , David Hildenbrand , Quentin Perret , Michael Roth , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: On Tue, Jul 25, 2023, Wei W Wang wrote: > On Wednesday, July 19, 2023 7:45 AM, Sean Christopherson wrote: > > +int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, > > + gfn_t gfn, kvm_pfn_t *pfn, int *max_order) { > > + pgoff_t index = gfn - slot->base_gfn + slot->gmem.pgoff; > > + struct kvm_gmem *gmem; > > + struct folio *folio; > > + struct page *page; > > + struct file *file; > > + > > + file = kvm_gmem_get_file(slot); > > + if (!file) > > + return -EFAULT; > > + > > + gmem = file->private_data; > > + > > + if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) { > > + fput(file); > > + return -EIO; > > + } > > + > > + folio = kvm_gmem_get_folio(file_inode(file), index); > > + if (!folio) { > > + fput(file); > > + return -ENOMEM; > > + } > > + > > + page = folio_file_page(folio, index); > > + > > + *pfn = page_to_pfn(page); > > + *max_order = compound_order(compound_head(page)); > > Maybe better to check if caller provided a buffer to get the max_order: > if (max_order) > *max_order = compound_order(compound_head(page)); > > This is what the previous version did (restrictedmem_get_page), > so that callers who only want to get a pfn don't need to define > an unused "order" param. My preference would be to require @max_order. I can kinda sorta see why a generic implementation (restrictedmem) would make the param optional, but with gmem being KVM-internal I think it makes sense to require the param. Even if pKVM doesn't _currently_ need/want the order of the backing allocation, presumably that's because hugepage support is still on the TODO list, not because pKVM fundamentally doesn't need to know the order of the backing allocation.