Re: [PATCH] KVM: x86/mmu: add lockdep check before lookup_address_in_mm()

Paolo Bonzini
2022-04-26T17:51:50Z

On 3/28/22 20:15, Sean Christopherson wrote:
>> lookup_address_in_mm() walks the host page table as if it is a
>> sequence of_static_ memory chunks. This is clearly dangerous.
> Yeah, it's broken. The proper fix is do something like what perf uses, or maybe
> just genericize and reuse the code from commit 8af26be06272
> ("perf/core: Fix arch_perf_get_page_size()).
>

Indeed, KVM could use perf_get_pgtable_size(). The conversion from the
result of *_leaf_size() to level is basically (ctz(size) - 12) / 9.

Alternatively, there are the three difference between
perf_get_page_size() and lookup_address_in_pgd():

* the *_offset_lockless() macros, which are unnecessary on x86

* READ_ONCE, which is important but in practice unlikely to make a
difference

* local_irq_{save,restore} around the walk

The last is the important one and it should be added to
lookup_address_in_pgd().

Paolo