From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [patch 06/11] KVM: introduce kvm->srcu and convert kvm_set_memory_region to SRCU update Date: Wed, 23 Dec 2009 16:33:06 +0200 Message-ID: <4B322A22.3080705@redhat.com> References: <20091223113833.742662117@redhat.com> <20091223114438.751996250@redhat.com> <4B320DF7.3070005@redhat.com> <20091223141941.GA14329@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:28248 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751669AbZLWOdK (ORCPT ); Wed, 23 Dec 2009 09:33:10 -0500 Received: from int-mx05.intmail.prod.int.phx2.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.18]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id nBNEX8dO005603 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 23 Dec 2009 09:33:08 -0500 In-Reply-To: <20091223141941.GA14329@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 12/23/2009 04:19 PM, Marcelo Tosatti wrote: > On Wed, Dec 23, 2009 at 02:32:55PM +0200, Avi Kivity wrote: > >> On 12/23/2009 01:38 PM, Marcelo Tosatti wrote: >> >>> Use two steps for memslot deletion: mark the slot invalid (which stops >>> instantiation of new shadow pages for that slot, but allows destruction), >>> then instantiate the new empty slot. >>> >>> Also simplifies kvm_handle_hva locking. >>> >>> >>> r = kvm_arch_prepare_memory_region(kvm,&new, old, user_alloc); >>> if (r) >>> goto out_free; >>> >>> >> r == 0 >> > Huh? kvm_arch_prepare_memory_region returns a suitable error code on > failure, 0 on success. > That's fine here, just pointing out you're inheriting this r == 0 later on. > kvm_iommu_map_pages returns 0 on success, error code otherwise? The > error code of kvm_iommu_map_pages was returned before the patchset, BTW. > Ok, then please fix it separately for easier backporting. >>> nr_mmu_pages = nr_pages * KVM_PERMILLE_MMU_PAGES / 1000; >>> nr_mmu_pages = max(nr_mmu_pages, >>> (unsigned int) KVM_MIN_ALLOC_MMU_PAGES); >>> + srcu_read_unlock(&kvm->srcu, idx); >>> >>> >>> >> Again, would like to move the srcu_locking to an outer scope. >> > This one was for documentation purposes only, since > kvm_mmu_calculate_mmu_pages is only called from commit_memory_region > (which mutually excludes itself). > > I can remove it if you'd prefer. > A comment should be sufficient. Otherwise someone might read the code and point out it's unnecessary. >> Shouldn't we already hold the srcu_lock as part of normal guest exit >> (similar to down_read() we do today)? >> > Yes, but: > > kvm_arch_vcpu_setup -> vmx_vcpu_reset -> vmx_set_cr0 -> enter_pmode > > So its called outside guest context path (memslot info is used outside > guest context in this case). > > Didn't we take slots_lock previously? If so, that's a bug. We should probably make all vcpu ioctls take slots_lock at top level, since many vcpu ioctls can be caused to access memory. -- error compiling committee.c: too many arguments to function