From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sean Christopherson Date: Tue, 14 Jan 2020 18:25:07 +0000 Subject: Re: [PATCH v4 16/19] KVM: Ensure validity of memslot with respect to kvm_get_dirty_log() Message-Id: <20200114182506.GF16784@linux.intel.com> List-Id: References: <20191217204041.10815-1-sean.j.christopherson@intel.com> <20191217204041.10815-17-sean.j.christopherson@intel.com> <20191224181930.GC17176@xz-x1> In-Reply-To: <20191224181930.GC17176@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Xu Cc: James Hogan , Paul Mackerras , Christian Borntraeger , Janosch Frank , Paolo Bonzini , Marc Zyngier , linux-arm-kernel@lists.infradead.org, Wanpeng Li , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , kvm@vger.kernel.org, David Hildenbrand , Joerg Roedel , Cornelia Huck , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, Vitaly Kuznetsov , kvmarm@lists.cs.columbia.edu, Jim Mattson On Tue, Dec 24, 2019 at 01:19:30PM -0500, Peter Xu wrote: > On Tue, Dec 17, 2019 at 12:40:38PM -0800, Sean Christopherson wrote: > > +int kvm_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log, > > + int *is_dirty, struct kvm_memory_slot **memslot) > > { > > struct kvm_memslots *slots; > > - struct kvm_memory_slot *memslot; > > int i, as_id, id; > > unsigned long n; > > unsigned long any = 0; > > > > + *memslot = NULL; > > + *is_dirty = 0; > > + > > as_id = log->slot >> 16; > > id = (u16)log->slot; > > if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS) > > return -EINVAL; > > > > slots = __kvm_memslots(kvm, as_id); > > - memslot = id_to_memslot(slots, id); > > - if (!memslot->dirty_bitmap) > > + *memslot = id_to_memslot(slots, id); > > + if (!(*memslot)->dirty_bitmap) > > return -ENOENT; > > > > - n = kvm_dirty_bitmap_bytes(memslot); > > + kvm_arch_sync_dirty_log(kvm, *memslot); > > Should this line belong to previous patch? No. The previous patch, "KVM: Provide common implementation for generic dirty log functions", is consolidating the implementation of dirty log functions for architectures with CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT=y. This code is being moved from s390's kvm_vm_ioctl_get_dirty_log(), as s390 doesn't select KVM_GENERIC_DIRTYLOG_READ_PROTECT. It's functionally a nop as kvm_arch_sync_dirty_log() is empty for PowerPC, the only other arch that doesn't select KVM_GENERIC_DIRTYLOG_READ_PROTECT. Arguably, the call to kvm_arch_sync_dirty_log() should be moved in a separate prep patch. It can't be a follow-on patch as that would swap the ordering of kvm_arch_sync_dirty_log() and kvm_dirty_bitmap_bytes(), etc... My reasoning for not splitting it to a separate patch is that prior to this patch, the common code and arch specific code are doing separate memslot lookups via id_to_memslot(), i.e. moving the kvm_arch_sync_dirty_log() call would operate on a "different" memslot. It can't actually be a different memslot because slots_lock is held, it just felt weird. All that being said, I don't have a strong opinion on moving the call to kvm_arch_sync_dirty_log() in a separate patch; IIRC, I vascillated between the two options when writing the code. If anyone wants it to be a separate patch I'll happily split it out. > > > + > > + n = kvm_dirty_bitmap_bytes(*memslot); > > > > for (i = 0; !any && i < n/sizeof(long); ++i) > > - any = memslot->dirty_bitmap[i]; > > + any = (*memslot)->dirty_bitmap[i]; > > > > - if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n)) > > + if (copy_to_user(log->dirty_bitmap, (*memslot)->dirty_bitmap, n)) > > return -EFAULT; > > > > if (any) > > -- > > 2.24.1 > > -- > Peter Xu >