Re: [PATCH v2] RISC-V: KVM: Fix compilation without RISCV_ISA_ZICBOM

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

On Thu, Oct 13, 2022 at 03:42:17PM +0200, Andrew Jones wrote:

> RISC-V: KVM: Fix compilation without RISCV_ISA_ZICBOM

nit: I know that this is what it fixes, but I think the commit subject
is a little misleading when it doesnt touch arch/riscv/kvm & has some
meaning for non-kvm too.

> riscv_cbom_block_size and riscv_init_cbom_blocksize() should always
> be available and riscv_init_cbom_blocksize() should always be invoked

Yup, I like where this is going...

> even when compiling without RISCV_ISA_ZICBOM enabled. This
> is because disabling RISCV_ISA_ZICBOM means "don't use zicbom
> instructions in the kernel" not "pretend there isn't zicbom, even
> when there is". When zicbom is available, whether the kernel enables
> its use with RISCV_ISA_ZICBOM or not, KVM will offer it to guests.

...right, I'll take your word for this part. You're the kvm people :)

> Ensure we can build KVM and that the block size is initialized even
> when compiling without RISCV_ISA_ZICBOM.
> 
> Fixes: 8f7e001e0325 ("RISC-V: Clean up the Zicbom block size probing")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>

Is cacheflush.c the "right" place for it? idk. But shaving that yak is a
waste of time imo. I like the unconditional availability & if ZICBOM is
off in the kernel I figure it should not matter that we set the
blocksize.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

> ---
>  arch/riscv/include/asm/cacheflush.h |  8 ------
>  arch/riscv/mm/cacheflush.c          | 38 ++++++++++++++++++++++++++
>  arch/riscv/mm/dma-noncoherent.c     | 41 -----------------------------
>  3 files changed, 38 insertions(+), 49 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> index 273ece6b622f..1470e556cdb1 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -42,16 +42,8 @@ void flush_icache_mm(struct mm_struct *mm, bool local);
>  
>  #endif /* CONFIG_SMP */
>  
> -/*
> - * The T-Head CMO errata internally probe the CBOM block size, but otherwise
> - * don't depend on Zicbom.
> - */
>  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);
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 6cb7d96ad9c7..8525f4a2d598 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -3,6 +3,7 @@
>   * Copyright (C) 2017 SiFive
>   */
>  
> +#include <linux/of.h>
>  #include <asm/cacheflush.h>
>  
>  #ifdef CONFIG_SMP
> @@ -86,3 +87,40 @@ void flush_icache_pte(pte_t pte)
>  		flush_icache_all();
>  }
>  #endif /* CONFIG_MMU */
> +
> +unsigned int riscv_cbom_block_size;
> +EXPORT_SYMBOL(riscv_cbom_block_size);
> +
> +void riscv_init_cbom_blocksize(void)
> +{
> +	struct device_node *node;
> +	unsigned long cbom_hartid;
> +	u32 val, probed_block_size;
> +	int ret;
> +
> +	probed_block_size = 0;
> +	for_each_of_cpu_node(node) {
> +		unsigned long hartid;
> +
> +		ret = riscv_of_processor_hartid(node, &hartid);
> +		if (ret)
> +			continue;
> +
> +		/* set block-size for cbom extension if available */
> +		ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
> +		if (ret)
> +			continue;
> +
> +		if (!probed_block_size) {
> +			probed_block_size = val;
> +			cbom_hartid = hartid;
> +		} else {
> +			if (probed_block_size != val)
> +				pr_warn("cbom-block-size mismatched between harts %lu and %lu\n",
> +					cbom_hartid, hartid);
> +		}
> +	}
> +
> +	if (probed_block_size)
> +		riscv_cbom_block_size = probed_block_size;
> +}
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> index b0add983530a..d919efab6eba 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -8,13 +8,8 @@
>  #include <linux/dma-direct.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/mm.h>
> -#include <linux/of.h>
> -#include <linux/of_device.h>
>  #include <asm/cacheflush.h>
>  
> -unsigned int riscv_cbom_block_size;
> -EXPORT_SYMBOL_GPL(riscv_cbom_block_size);
> -
>  static bool noncoherent_supported;
>  
>  void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
> @@ -77,42 +72,6 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  	dev->dma_coherent = coherent;
>  }
>  
> -#ifdef CONFIG_RISCV_ISA_ZICBOM
> -void riscv_init_cbom_blocksize(void)
> -{
> -	struct device_node *node;
> -	unsigned long cbom_hartid;
> -	u32 val, probed_block_size;
> -	int ret;
> -
> -	probed_block_size = 0;
> -	for_each_of_cpu_node(node) {
> -		unsigned long hartid;
> -
> -		ret = riscv_of_processor_hartid(node, &hartid);
> -		if (ret)
> -			continue;
> -
> -		/* set block-size for cbom extension if available */
> -		ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
> -		if (ret)
> -			continue;
> -
> -		if (!probed_block_size) {
> -			probed_block_size = val;
> -			cbom_hartid = hartid;
> -		} else {
> -			if (probed_block_size != val)
> -				pr_warn("cbom-block-size mismatched between harts %lu and %lu\n",
> -					cbom_hartid, hartid);
> -		}
> -	}
> -
> -	if (probed_block_size)
> -		riscv_cbom_block_size = probed_block_size;
> -}
> -#endif
> -
>  void riscv_noncoherent_supported(void)
>  {
>  	WARN(!riscv_cbom_block_size,
> -- 
> 2.37.3
> 
> 
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