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SubjectRe: [PATCH][next] KVM: x86: Fix allocation sizeof argument
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On 05/10/21 17:41, Sean Christopherson wrote:
>> 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).

That's not a huge deal because the syscall is failing. So as long as
it's not leaked forever, it's okay. The problem is the
WARN_ON(slot->arch.rmap[i]), or the missing check in
kvm_page_track_enable_mmu_write_tracking, but that's easily fixed. I'd
even remove the call to memslot_rmaps_free.

> 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.

I was thinking the separate flow (not so much the flag) is needed
because, if KVMGT is enabled, gfn_track is allocated unconditionally.
rmaps are added on top of that if shadow paging is enabled; but
kvm_page_track_create_memslot will have already created the counter,
including the one for KVM_PAGE_TRACK_WRITE.

But looking at the code again, I guess you could call
kvm_page_track_enable_mmu_write_tracking inside alloc_all_memslots_rmaps
(with a little bit of renaming), and with that the flag would go away.

I'll take a look tomorrow, but I'd rather avoid reverting the patch.

Thanks,

Paolo

> Paolo, is it too late to just drop the original deae4a10f166 ("KVM: x86: only
> allocate gfn_track when necessary")?
>

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