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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 3B9D2C4CECC for ; Mon, 27 Apr 2020 18:10:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1E511206D4 for ; Mon, 27 Apr 2020 18:10:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726260AbgD0SKz (ORCPT ); Mon, 27 Apr 2020 14:10:55 -0400 Received: from mga03.intel.com ([134.134.136.65]:33437 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725995AbgD0SKz (ORCPT ); Mon, 27 Apr 2020 14:10:55 -0400 IronPort-SDR: Cr2qcAYLXeFLjmMsMH/gKkHw90+P/5bdOo299Km3loBxnj68/BxL0nah3wW4K+BgYev6Yl2SON r2RCdz9XMuNg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Apr 2020 11:10:55 -0700 IronPort-SDR: gV6505nVR9Uf00DxSwVzlwBzUTwspCl7aZaDPS1ZznM26yKSLJnV+rAvnIZvi5+atxE0vHrfcb Otm0GQkrNr+Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,325,1583222400"; d="scan'208";a="292583458" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga002.fm.intel.com with ESMTP; 27 Apr 2020 11:10:54 -0700 Date: Mon, 27 Apr 2020 11:10:54 -0700 From: Sean Christopherson To: Peter Xu Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kevin Tian , "Michael S . Tsirkin" , Jason Wang , Christophe de Dinechin , Yan Zhao , Alex Williamson , Paolo Bonzini , Vitaly Kuznetsov , "Dr . David Alan Gilbert" Subject: Re: [PATCH v8 03/14] KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] Message-ID: <20200427181054.GL14870@linux.intel.com> References: <20200331190000.659614-1-peterx@redhat.com> <20200331190000.659614-4-peterx@redhat.com> <20200423203944.GS17824@linux.intel.com> <20200424152151.GB41816@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200424152151.GB41816@xz-x1> 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 Fri, Apr 24, 2020 at 11:21:51AM -0400, Peter Xu wrote: > On Thu, Apr 23, 2020 at 01:39:44PM -0700, Sean Christopherson wrote: > > On Tue, Mar 31, 2020 at 02:59:49PM -0400, Peter Xu wrote: > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > index 1b6d9ac9533c..faa702c4d37b 100644 > > > --- a/arch/x86/kvm/x86.c > > > +++ b/arch/x86/kvm/x86.c > > > @@ -9791,7 +9791,32 @@ void kvm_arch_sync_events(struct kvm *kvm) > > > kvm_free_pit(kvm); > > > } > > > > > > -int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > > > +#define ERR_PTR_USR(e) ((void __user *)ERR_PTR(e)) > > > > Heh, my first thought when reading the below code was "cool, I didn't know > > there was ERR_PTR_USR!". This probably should be in include/linux/err.h, > > or maybe a new arch specific implementation if it's not universally safe. > > Yeah, I just wanted to avoid introducing things in common headers before I'm > sure it'll be used in the rest of the world.. We can always replace them with > a global definition when it comes. Gotcha. > > An alternative, which looks enticing given that proper user variants will > > be a bit of an explosion, would be to do: > > > > static void *____x86_set_memory_region(...) > > { > > > > } > > > > void __user *__x86_set_memory_region(...) > > { > > return (void __user *)____x86_set_memory_region(...); > > } > > > > A second alternative would be to return an "unsigned long", i.e. force the > > one function that actually accesses the hva to do the cast. I think I like > > this option the best as it would minimize the churn in > > __x86_set_memory_region(). Callers can use IS_ERR_VALUE() to detect failure. > > If you won't mind, I would prefer a 2nd opinion (maybe Paolo?) so we can > consolidate the idea before I change them... (I would for sure still prefer the > current approach for simplicity since after all I don't have strong opionion..) Definitely makes sense for Paolo to weigh in. > > > +/** > > > + * __x86_set_memory_region: Setup KVM internal memory slot > > > + * > > > + * @kvm: the kvm pointer to the VM. > > > + * @id: the slot ID to setup. > > > + * @gpa: the GPA to install the slot (unused when @size == 0). > > > + * @size: the size of the slot. Set to zero to uninstall a slot. > > > + * > > > + * This function helps to setup a KVM internal memory slot. Specify > > > + * @size > 0 to install a new slot, while @size == 0 to uninstall a > > > + * slot. The return code can be one of the following: > > > + * > > > + * HVA: on success (uninstall will return a bogus HVA) > > > > I think it's important to call out that it returns '0' on uninstall, e.g. > > otherwise it's not clear how a caller can detect failure. > > It will "return (0xdeadull << 48)" as you proposed in abbed4fa94f6? :-) > > Frankly speaking I always preferred zero but that's just not true any more > after above change. This also reminded me that maybe we should also return the > same thing at [1] below. Ah, I was looking at this code: if (!slot || !slot->npages) return 0; That means deletion returns different success values for "deletion was a nop" and "deletion was successful". The nop path should probably return (or fill in) "(unsigned long)(0xdeadull << 48)" as well. > > > + * -errno: on error > > > + * > > > + * The caller should always use IS_ERR() to check the return value > > > + * before use. Note, the KVM internal memory slots are guaranteed to > > > + * remain valid and unchanged until the VM is destroyed, i.e., the > > > + * GPA->HVA translation will not change. However, the HVA is a user > > > + * address, i.e. its accessibility is not guaranteed, and must be > > > + * accessed via __copy_{to,from}_user(). > > > + */ > > > +void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, > > > + u32 size) > > > { > > > int i, r; > > > unsigned long hva, uninitialized_var(old_npages); > > > @@ -9800,12 +9825,12 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > > > > > > /* Called with kvm->slots_lock held. */ > > > if (WARN_ON(id >= KVM_MEM_SLOTS_NUM)) > > > - return -EINVAL; > > > + return ERR_PTR_USR(-EINVAL); > > > > > > slot = id_to_memslot(slots, id); > > > if (size) { > > > if (slot && slot->npages) > > > - return -EEXIST; > > > + return ERR_PTR_USR(-EEXIST); > > > > > > /* > > > * MAP_SHARED to prevent internal slot pages from being moved > > > @@ -9814,10 +9839,10 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > > > hva = vm_mmap(NULL, 0, size, PROT_READ | PROT_WRITE, > > > MAP_SHARED | MAP_ANONYMOUS, 0); > > > if (IS_ERR((void *)hva)) > > > > IS_ERR_VALUE() can be used to avoid the double cast. > > Agreed. But it's a context cleanup, so I normally will keep it as is (or use a > standalone patch). > > > > > > - return PTR_ERR((void *)hva); > > > + return (void __user *)hva; > > > > If we still want to go down the route of ERR_PTR_USR, then an ERR_CAST_USR > > seems in order. > > Sure. But I'll still keep it kvm-only if you won't mind... > > > > > > } else { > > > if (!slot || !slot->npages) > > > - return 0; > > > + return ERR_PTR_USR(0); > > [1] > > > > > "return ERR_PTR_USR(NULL)" or "return NULL" would be more intuitive. Moot > > point if the return is changed to "unsigned long". > > ERR_PTR_USR() takes a "long". I can use ERR_CAST_USR(NULL) if you prefer me to > explicitly use NULL. > > Thanks, > > -- > Peter Xu >