Re: [PATCH v4] RISC-V: Clean up the Zicbom block size probing

[Nathan Chancellor <nathan@kernel.org>]

On Mon, Sep 12, 2022 at 11:48:01PM +0100, Conor Dooley wrote:
> From: Palmer Dabbelt <palmer@rivosinc.com>
> 
> This fixes two issues: I truncated the warning's hart ID when porting to
> the 64-bit hart ID code, and the original code's warning handling could
> fire on an uninitialized hart ID.
> 
> The biggest change here is that riscv_cbom_block_size is no longer
> initialized, as IMO the default isn't sane: there's nothing in the ISA
> that mandates any specific cache block size, so falling back to one will
> just silently produce the wrong answer on some systems.  This also
> changes the probing order so the cache block size is known before
> enabling Zicbom support.
> 
> CC: stable@vger.kernel.org
> CC: Andrew Jones <ajones@ventanamicro.com>
> CC: Heiko Stuebner <heiko@sntech.de>
> CC: Atish Patra <atishp@rivosinc.com>
> Fixes: 3aefb2ee5bdd ("riscv: implement Zicbom-based CMO instructions + the t-head variant")
> Fixes: 1631ba1259d6 ("riscv: Add support for non-coherent devices using zicbom extension")
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Conor Dooley <conor.dooley@microchip.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> [Conor: fixed the redefinition errors]
> Tested-by: Conor Dooley <conor.dooley@microchip.com>
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Build-tested-by: Nathan Chancellor <nathan@kernel.org>

Thanks a lot for continuing to chase this!

> ---
> Hey Palmer,
> w/ LPC etc I figure it's highly unlikely you'd have this respun
> in time to have it applied this week. I dropped all the tested
> and reviewed -by tags since this patch has been changed a fair
> bit back and forth since the tags were left. Checked it on my
> D1 to make sure nothing blew up.. if this could make this weeks
> rc, that'd be great so that the clang allmodconfig builds are
> working again.
> Conor.
> ---
>  arch/riscv/errata/thead/errata.c    |  1 +
>  arch/riscv/include/asm/cacheflush.h |  1 +
>  arch/riscv/kernel/setup.c           |  2 +-
>  arch/riscv/mm/dma-noncoherent.c     | 23 +++++++++++++----------
>  4 files changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 202c83f677b2..96648c176f37 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -37,6 +37,7 @@ static bool errata_probe_cmo(unsigned int stage,
>  	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
>  		return false;
>  
> +	riscv_cbom_block_size = L1_CACHE_BYTES;
>  	riscv_noncoherent_supported();
>  	return true;
>  #else
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> index a60acaecfeda..a89c005b4bbf 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -43,6 +43,7 @@ void flush_icache_mm(struct mm_struct *mm, bool local);
>  #endif /* CONFIG_SMP */
>  
>  #ifdef CONFIG_RISCV_ISA_ZICBOM
> +extern unsigned int riscv_cbom_block_size;
>  void riscv_init_cbom_blocksize(void);
>  #else
>  static inline void riscv_init_cbom_blocksize(void) { }
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 95ef6e2bf45c..2dfc463b86bb 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -296,8 +296,8 @@ void __init setup_arch(char **cmdline_p)
>  	setup_smp();
>  #endif
>  
> -	riscv_fill_hwcap();
>  	riscv_init_cbom_blocksize();
> +	riscv_fill_hwcap();
>  	apply_boot_alternatives();
>  }
>  
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> index cd2225304c82..e3f9bdf47c5f 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -12,7 +12,7 @@
>  #include <linux/of_device.h>
>  #include <asm/cacheflush.h>
>  
> -static unsigned int riscv_cbom_block_size = L1_CACHE_BYTES;
> +unsigned int riscv_cbom_block_size;
>  static bool noncoherent_supported;
>  
>  void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
> @@ -79,38 +79,41 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  void riscv_init_cbom_blocksize(void)
>  {
>  	struct device_node *node;
> +	unsigned long cbom_hartid;
> +	u32 val, probed_block_size;
>  	int ret;
> -	u32 val;
>  
> +	probed_block_size = 0;
>  	for_each_of_cpu_node(node) {
>  		unsigned long hartid;
> -		int cbom_hartid;
>  
>  		ret = riscv_of_processor_hartid(node, &hartid);
>  		if (ret)
>  			continue;
>  
> -		if (hartid < 0)
> -			continue;
> -
>  		/* set block-size for cbom extension if available */
>  		ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
>  		if (ret)
>  			continue;
>  
> -		if (!riscv_cbom_block_size) {
> -			riscv_cbom_block_size = val;
> +		if (!probed_block_size) {
> +			probed_block_size = val;
>  			cbom_hartid = hartid;
>  		} else {
> -			if (riscv_cbom_block_size != val)
> -				pr_warn("cbom-block-size mismatched between harts %d and %lu\n",
> +			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,
> +	     "Non-coherent DMA support enabled without a block size\n");
>  	noncoherent_supported = true;
>  }
> -- 
> 2.37.1
>