Re: [PATCH] KVM: arm64: account pKVM reclaim against the VM mm

[Bradley Morgan]

On June 22, 2026 10:16:18 AM GMT+01:00, Marc Zyngier <maz@xxxxxxxxxx>
wrote:
>On Mon, 22 Jun 2026 09:32:45 +0100,
>Fuad Tabba <fuad.tabba@xxxxxxxxx> wrote:
>> 
>> On Sun, 21 Jun 2026 at 22:32, Bradley Morgan <include@xxxxxxxxx> wrote:
>> >
>> > Protected guest faults charge long term pins to the VM's mm. Teardown
>> > can run later from file release, where current->mm may be unrelated.
>> >
>> > Drop the charge from kvm->mm instead.
>> >
>> > Fixes: 4e6e03f9eadd ("KVM: arm64: Hook up reclaim hypercall to
>pkvm_pgtable_stage2_destroy()")
>> > Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
>> 
>> Reproduced by creating a protected VM, running the vCPU to fault in a
>> page, then forking and having the child close the last fd reference.
>> Without the fix, the parent's VmLck leaks (the reclaim decrements the
>> child's mm, which is freed on exit). With the fix the parent's VmLck
>> returns to zero.
>> 
>> One minor observation: account_locked_vm() also passes `current` as
>> the task pointer to __account_locked_vm(), but on the decrement path
>> that is only used in the pr_debug log line, so it is technically wrong
>> but functionally harmless.

I agree with marc here. Maybe awkward.


I tested it on my pixel 7! :)

>I don't think this is wrong. Awkward, maybe. It is just that the
>rlimit check and the accounting may be different contexts, and the
>pr_debug() call covers both inc and dec.
>
>>
>> Reviewed-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>
>> Tested-by: Fuad Tabba < fuad.tabba@xxxxxxxxx>

Thanks for the review! :)

Cheers!

>Thanks,
>
>	M.
>
>