Re: [PATCH] RISC-V: KVM: fixup undefined reference to riscv_cbom_block_size

[Conor Dooley <conor.dooley@microchip.com>]

On Mon, Oct 10, 2022 at 09:33:29AM +0800, Vernon Yang wrote:
> When some RISC-V compilers do not support the Zicbom extension,
> the build system auto disable the CONFIG_RISCV_ISA_ZICBOM, so the
> source code of the relevant function is not compiled, resulting
> in the definition of the riscv_cbom_block_size variable cannot
> be found

Hmm, my understanding was that riscv_cbom_block_size was not supposed to
depend on CONFIG_RISCV_ISA_ZICBOM because the thead is able to use it
even if the toolchain does not support it.

The code in cacheflush.h looks like:
extern unsigned int riscv_cbom_block_size;
#ifdef CONFIG_RISCV_ISA_ZICBOM
void riscv_init_cbom_blocksize(void);
#else
static inline void riscv_init_cbom_blocksize(void) { }
#endif

#ifdef CONFIG_RISCV_DMA_NONCOHERENT
void riscv_noncoherent_supported(void);
#endif

It's early and I only had a quick look but I think that this is not
defined because RISCV_DMA_NONCOHERENT is not defined, not because of
RISCV_ISA_ZICBOM. I'm not the KVM maintainer, but I dislike #ifdefery
in c files, so it'd be nice I think to sort this out in the header and
not have to worry about guarding the variable.

That's my 0.02 €..

Thanks,
Conor.

 
> So add conditional compilation to fix it
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Vernon Yang <vernon2gm@gmail.com>
> ---
>  arch/riscv/kvm/vcpu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> index a032c4f0d600..08a6c3cb695d 100644
> --- a/arch/riscv/kvm/vcpu.c
> +++ b/arch/riscv/kvm/vcpu.c
> @@ -256,7 +256,7 @@ static int kvm_riscv_vcpu_get_reg_config(struct kvm_vcpu *vcpu,
>  	unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
>  					    KVM_REG_SIZE_MASK |
>  					    KVM_REG_RISCV_CONFIG);
> -	unsigned long reg_val;
> +	unsigned long reg_val = 0;
>  
>  	if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
>  		return -EINVAL;
> @@ -268,7 +268,9 @@ static int kvm_riscv_vcpu_get_reg_config(struct kvm_vcpu *vcpu,
>  	case KVM_REG_RISCV_CONFIG_REG(zicbom_block_size):
>  		if (!riscv_isa_extension_available(vcpu->arch.isa, ZICBOM))
>  			return -EINVAL;
> +#ifdef CONFIG_RISCV_ISA_ZICBOM
>  		reg_val = riscv_cbom_block_size;
> +#endif
>  		break;
>  	default:
>  		return -EINVAL;
> -- 
> 2.25.1
> 
>