Re: [PATCH] KVM: arm64: Stop sparse from moaning at __hyp_this_cpu_ptr

Marc Zyngier
2020-06-08T16:31:28Z

On 2020-06-08 16:00, Andrew Scull wrote:
> On Mon, Jun 08, 2020 at 09:57:31AM +0100, Marc Zyngier wrote:
>> Sparse complains that __hyp_this_cpu_ptr() returns something
>> that is flagged noderef and not in the correct address space
>> (both being the result of the __percpu annotation).
>>
>> Pretend that __hyp_this_cpu_ptr() knows what it is doing by
>> forcefully casting the pointer with __kernel __force.
>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>> arch/arm64/include/asm/kvm_asm.h | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_asm.h
>> b/arch/arm64/include/asm/kvm_asm.h
>> index 0c9b5fc4ba0a..82691406d493 100644
>> --- a/arch/arm64/include/asm/kvm_asm.h
>> +++ b/arch/arm64/include/asm/kvm_asm.h
>> @@ -81,12 +81,17 @@ extern u32 __kvm_get_mdcr_el2(void);
>>
>> extern char __smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ];
>>
>> -/* Home-grown __this_cpu_{ptr,read} variants that always work at HYP
>> */
>> +/*
>> + * Home-grown __this_cpu_{ptr,read} variants that always work at HYP,
>> + * provided that sym is really a *symbol* and not a pointer obtained
>> from
>
> Look at `this_cpu_ptr` one thing that stood out was `__verify_pcpu_ptr`
> that is documented to be suitable for used in custom per CPU macros. I
> didn't get how it worked (a type check?) but maybe it would work here
> to validate the argment was indeed a per CPU symbol?

It only works for sparse, but that is definitely a good addition while
we're fixing the sparse compliance.

Thanks,

M.
--
Jazz is not dead. It just smells funny...