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")?
