From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Fri, 15 Feb 2013 19:42:05 +0100 (CET) Received: from mx1.redhat.com ([209.132.183.28]:37251 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6827660Ab3BOSmEq0bf8 (ORCPT ); Fri, 15 Feb 2013 19:42:04 +0100 Received: from int-mx12.intmail.prod.int.phx2.redhat.com (int-mx12.intmail.prod.int.phx2.redhat.com [10.5.11.25]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id r1FIg1eN029458 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Fri, 15 Feb 2013 13:42:01 -0500 Received: from dhcp-1-237.tlv.redhat.com (dhcp-4-26.tlv.redhat.com [10.35.4.26]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id r1FIfx3A024722; Fri, 15 Feb 2013 13:42:00 -0500 Received: by dhcp-1-237.tlv.redhat.com (Postfix, from userid 13519) id 58B8D18D479; Fri, 15 Feb 2013 20:41:59 +0200 (IST) Date: Fri, 15 Feb 2013 20:41:59 +0200 From: Gleb Natapov To: Sanjay Lal Cc: kvm@vger.kernel.org, linux-mips@linux-mips.org Subject: Re: [PATCH v2 07/18] KVM/MIPS32: MMU/TLB operations for the Guest. Message-ID: <20130215184159.GA16755@redhat.com> References: <1353551656-23579-1-git-send-email-sanjayl@kymasys.com> <1353551656-23579-8-git-send-email-sanjayl@kymasys.com> <20130206120820.GN23213@redhat.com> <69F3ED2A-A9B3-4046-9B40-98125ED5A8FB@kymasys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69F3ED2A-A9B3-4046-9B40-98125ED5A8FB@kymasys.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.25 X-archive-position: 35776 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: gleb@redhat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips Return-Path: On Fri, Feb 15, 2013 at 01:19:29PM -0500, Sanjay Lal wrote: > > On Feb 6, 2013, at 7:08 AM, Gleb Natapov wrote: > > >> > >> +static void kvm_mips_map_page(struct kvm *kvm, gfn_t gfn) > >> +{ > >> + pfn_t pfn; > >> + > >> + if (kvm->arch.guest_pmap[gfn] != KVM_INVALID_PAGE) > >> + return; > >> + > >> + pfn =kvm_mips_gfn_to_pfn(kvm, gfn); > > This call should be in srcu read section since it access memory slots which > > are srcu protected. You should test with RCU debug enabled. > > kvm_mips_gfn_to_pfn just maps to gfn_to_pfn. I don't see an instance where gfn_to_pfn is in a scru read section? > Where are you looking? On x86 if vcpu is not in a guest mode it is in srcu read section. The lock is taken immediately after exit and released before entry. This is because x86 access memory slots a lot. Other arches, that do not access memory slots as much, take the lock around each individual access. As far as I see this is the only place in MIPS kvm where this is needed. > > > >> > >> + > >> +uint32_t kvm_get_inst(uint32_t *opc, struct kvm_vcpu *vcpu) > >> +{ > >> + uint32_t inst; > >> + struct mips_coproc *cop0 __unused = vcpu->arch.cop0; > >> + int index; > >> + ulong paddr, flags; > >> + > >> + if (KVM_GUEST_KSEGX((ulong) opc) < KVM_GUEST_KSEG0 || > >> + KVM_GUEST_KSEGX((ulong) opc) == KVM_GUEST_KSEG23) { > >> + local_irq_save(flags); > >> + index = kvm_mips_host_tlb_lookup(vcpu, (ulong) opc); > >> + if (index >= 0) { > >> + inst = *(opc); > > Here and in some more places below you access __user memory. Shouldn't you > > use get_user() to access it? What prevents the kernel crash by access fault here > > if userspace remaps the memory to be non-readable? Hmm, may be it uses > > guest translation here so it cannot happen, but still, sparse will not > > be happy and kvm_mips_translate_guest_kseg0_to_hpa() case below uses > > host translation anyway. > > > Actually, I don't need the __user declaration in most cases, since KVM/MIPS handles mapping the page (if needed) and does not rely on the usual kernel mechanisms. Yes I see that you check/populate tlb for non KVM_GUEST_KSEG0 access, for kvm_mips_translate_guest_kseg0_to_hpa() you do not, but now I notice that you are not using the address directly but uses CKSEG0ADDR() on it, which, as far as I can tell, gives you kernel mapping for the page, correct? Why this is better than using get_user()? To save tlb entries? -- Gleb.