Messages in this thread Patch in this message | | | Date | Tue, 5 Oct 2021 15:41:42 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH][next] KVM: x86: Fix allocation sizeof argument |
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On Fri, Oct 01, 2021, Colin King wrote: > From: Colin Ian King <colin.king@canonical.com> > > The allocation for *gfn_track should be for a slot->npages lot of > short integers, however the current allocation is using sizeof(*gfn_track) > and that is the size of a pointer, which is too large. Fix this by > using sizeof(**gfn_track) instead. > > Addresses-Coverity: ("Wrong sizeof argument") > Fixes: 35b330bba6a7 ("KVM: x86: only allocate gfn_track when necessary") > Signed-off-by: Colin Ian King <colin.king@canonical.com> > --- > arch/x86/kvm/mmu/page_track.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c > index bb5d60bd4dbf..5b785a5f7dc9 100644 > --- a/arch/x86/kvm/mmu/page_track.c > +++ b/arch/x86/kvm/mmu/page_track.c > @@ -92,7 +92,7 @@ int kvm_page_track_enable_mmu_write_tracking(struct kvm *kvm) > slots = __kvm_memslots(kvm, i); > kvm_for_each_memslot(slot, slots) { > gfn_track = slot->arch.gfn_track + KVM_PAGE_TRACK_WRITE; > - *gfn_track = kvcalloc(slot->npages, sizeof(*gfn_track), > + *gfn_track = kvcalloc(slot->npages, sizeof(**gfn_track), > GFP_KERNEL_ACCOUNT);
Eww (not your patch, the original code). IMO the double indirection is completely unnecessary, e.g. I find this far easier to follow
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c index bb5d60bd4dbf..8cae41b831dd 100644 --- a/arch/x86/kvm/mmu/page_track.c +++ b/arch/x86/kvm/mmu/page_track.c @@ -75,7 +75,7 @@ int kvm_page_track_enable_mmu_write_tracking(struct kvm *kvm) { struct kvm_memslots *slots; struct kvm_memory_slot *slot; - unsigned short **gfn_track; + unsigned short *gfn_track; int i; if (write_tracking_enabled(kvm)) @@ -91,13 +91,13 @@ int kvm_page_track_enable_mmu_write_tracking(struct kvm *kvm) for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) { slots = __kvm_memslots(kvm, i); kvm_for_each_memslot(slot, slots) { - gfn_track = slot->arch.gfn_track + KVM_PAGE_TRACK_WRITE; - *gfn_track = kvcalloc(slot->npages, sizeof(*gfn_track), - GFP_KERNEL_ACCOUNT); - if (*gfn_track == NULL) { + gfn_track = kvcalloc(slot->npages, sizeof(*gfn_track), + GFP_KERNEL_ACCOUNT); + if (gfn_track == NULL) { mutex_unlock(&kvm->slots_arch_lock); return -ENOMEM; } + slot->arch.gfn_track[KVM_PAGE_TRACK_WRITE] = gfn_track; } }
> if (*gfn_track == NULL) { > mutex_unlock(&kvm->slots_arch_lock);
Hrm, this fails to free the gfn_track allocations for previous memslots. The on-demand rmaps code has the exact same bug (it frees rmaps for previous lpages in the _current_ slot, but does not free previous slots).
And having two separate flows (and flags) for rmaps vs. gfn_track is pointless, and means we have to maintain two near-identical copies of non-obvious code.
Paolo, is it too late to just drop the original deae4a10f166 ("KVM: x86: only allocate gfn_track when necessary")?
> -- > 2.32.0 >
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