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

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

[Marc Zyngier]

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
+ * a data structure. As for SHIFT_PERCPU_PTR(), the creative casting keeps
+ * sparse quiet.
+ */
 #define __hyp_this_cpu_ptr(sym)						\
 	({								\
 		void *__ptr = hyp_symbol_addr(sym);			\
 		__ptr += read_sysreg(tpidr_el2);			\
-		(typeof(&sym))__ptr;					\
+		(typeof(sym) __kernel __force *)__ptr;			\
 	 })
 
 #define __hyp_this_cpu_read(sym)					\
-- 
2.26.2


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

[Andrew Scull]

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?

> + * a data structure. As for SHIFT_PERCPU_PTR(), the creative casting keeps
> + * sparse quiet.
> + */
>  #define __hyp_this_cpu_ptr(sym)						\
>  	({								\
>  		void *__ptr = hyp_symbol_addr(sym);			\
>  		__ptr += read_sysreg(tpidr_el2);			\
> -		(typeof(&sym))__ptr;					\
> +		(typeof(sym) __kernel __force *)__ptr;			\
>  	 })
>  
>  #define __hyp_this_cpu_read(sym)					\

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

[Marc Zyngier]

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...

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