Messages in this thread | | | Date | Fri, 29 Apr 2022 16:45:03 +0200 | From | Paolo Bonzini <> | Subject | Re: [PATCH] KVM: x86/mmu: fix potential races when walking host page table |
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On 4/29/22 16:35, Sean Christopherson wrote: > On Fri, Apr 29, 2022, Paolo Bonzini wrote: >>> +out: >>> + local_irq_restore(flags); >>> + return level; >>> +} >>> +EXPORT_SYMBOL_GPL(kvm_lookup_address_level_in_mm); >> >> Exporting is not needed. >> >> Thanks for writing the walk code though. I'll adapt it and integrate the >> patch. > > But why are we fixing this only in KVM? I liked the idea of stealing perf's > implementation because it was a seemlingly perfect fit and wouldn't introduce > new code (ignoring wrappers, etc...). > > We _know_ that at least one subsystem is misusing lookup_address_in_pgd() and > given that its wrappers are exported, I highly doubt KVM is the only offender. > It really feels like we're passing the buck here by burying the fix in KVM.
There are two ways to do it:
* having a generic function in mm/. The main issue there is the lack of a PG_LEVEL_{P4D,PUD,PMD,PTE} enum at the mm/ level. We could use (ctz(x) - 12) / 9 to go from size to level, but it's ugly and there could be architectures with heterogeneous page table sizes.
* having a generic function in arch/x86/. In this case KVM seems to be the odd one that doesn't need the PTE. For example vc_slow_virt_to_phys needs the PTE, and needs the size rather than the "level" per se.
So for now I punted, while keeping open the door for moving code from arch/x86/kvm/ to mm/ if anyone else (even other KVM ports) need the same logic.
Paolo
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