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Date: Tue, 14 Jan 2020 10:25:07 -0800 From: Sean Christopherson <sean.j.christopherson@...el.com> To: Peter Xu <peterx@...hat.com> Cc: James Hogan <jhogan@...nel.org>, Paul Mackerras <paulus@...abs.org>, Christian Borntraeger <borntraeger@...ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, linux-arm-kernel@...ts.infradead.org, Wanpeng Li <wanpengli@...cent.com>, Philippe Mathieu-Daudé <f4bug@...at.org>, kvm@...r.kernel.org, David Hildenbrand <david@...hat.com>, Joerg Roedel <joro@...tes.org>, Cornelia Huck <cohuck@...hat.com>, linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org, Vitaly Kuznetsov <vkuznets@...hat.com>, kvmarm@...ts.cs.columbia.edu, Jim Mattson <jmattson@...gle.com> Subject: Re: [PATCH v4 16/19] KVM: Ensure validity of memslot with respect to kvm_get_dirty_log() 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 >
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