Re: [PATCH 2/4] KVM: Avoid checking huge page mappings inget_dirty_log()

[Takuya Yoshikawa]

Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote:

> 
> This is a race with hugetlbfs which is not an issue ATM (it is 
> hidden by the removal of huge sptes in get_dirty).

Thank you!
I did not notice this possibility at all.

...

> It can be fixed with a preceding patch that checks whether
> slot->dirty_bitmap value changes between mapping_level and after
> mmu_lock acquision, similarly to mmu_seq. Also please add a 
> WARN_ON in mmu_set_spte if(slot->dirty_bitmap && level > 1).
> And document it clearly.

We may also be able to change the "if (slot->dirty_bitmap)" check to
use another flag so that we can delay the start of logging until
mmu_lock acquisition in kvm_set_memory_region().

Looking dirty_bitmap directly should be limited to when we are in
get_dirty functions.

	Takuya
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