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 2FD93C55191 for ; Thu, 23 Apr 2020 20:39:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1621020784 for ; Thu, 23 Apr 2020 20:39:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726414AbgDWUjp (ORCPT ); Thu, 23 Apr 2020 16:39:45 -0400 Received: from mga05.intel.com ([192.55.52.43]:49524 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725884AbgDWUjp (ORCPT ); Thu, 23 Apr 2020 16:39:45 -0400 IronPort-SDR: 2IQp2gPFueeTo17yy5Scm5COEeKY9WhjQyNTYngkw4Re5Oe4v0zhSMk/hXQusQDeUyaCCTXiHD OC/thd7/G4EA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Apr 2020 13:39:44 -0700 IronPort-SDR: PAytE2gd3PBGaQ1vc8eGBqEXx4D7ZP6om29YOEArslB7dEk2ZEyvxu6H5jlS9TrOay2cxKyWBa mzhGhdIVBhdQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,309,1583222400"; d="scan'208";a="292396043" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga008.jf.intel.com with ESMTP; 23 Apr 2020 13:39:44 -0700 Date: Thu, 23 Apr 2020 13:39:44 -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: <20200423203944.GS17824@linux.intel.com> References: <20200331190000.659614-1-peterx@redhat.com> <20200331190000.659614-4-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200331190000.659614-4-peterx@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, 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. 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. > +/** > + * __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. > + * -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. > - 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. > } else { > if (!slot || !slot->npages) > - return 0; > + return ERR_PTR_USR(0); "return ERR_PTR_USR(NULL)" or "return NULL" would be more intuitive. Moot point if the return is changed to "unsigned long". > > /* > * Stuff a non-canonical value to catch use-after-delete. This > @@ -9838,13 +9863,13 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > m.memory_size = size; > r = __kvm_set_memory_region(kvm, &m); > if (r < 0) > - return r; > + return ERR_PTR_USR(r); > } > > if (!size) > vm_munmap(hva, old_npages * PAGE_SIZE); > > - return 0; > + return (void __user *)hva; > } > EXPORT_SYMBOL_GPL(__x86_set_memory_region); > > -- > 2.24.1 >