[PATCH v7 3/7] powerpc/pmem: Add flush routines using new pmem store and sync instruction

[Christophe Leroy]

Le 01/07/2020 à 09:22, Aneesh Kumar K.V a écrit :
> Start using dcbstps; phwsync; sequence for flushing persistent memory range.
> The new instructions are implemented as a variant of dcbf and hwsync and on
> P8 and P9 they will be executed as those instructions. We avoid using them on
> older hardware. This helps to avoid difficult to debug bugs.
> 

Before this patch, the flush was done for all.
After this patch, IIUC the flush is done only on CPUs having feature 
CPU_FTR_ARCH_207S.

What about other CPUs ?

I don't know much about PMEM, my concern is about the UACCESS_FLUSHCACHE 
API introduced by commit 6c44741d75a2 ("powerpc/lib: Implement 
UACCESS_FLUSHCACHE API")

After your patch, __copy_from_user_flushcache() and memcpy_flushcache() 
are not doing cache flush anymore.

Is that intended ?

I'm trying to optimise some ALSA driver that does copy_from_user + 
cache_flush for DMA, and I was wondering if using 
__copy_from_user_flushcache() was an alternative.

Or is it __copy_from_user_inatomic_nocache() which has to be done for that ?

Thanks
Christophe


> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> ---
>   arch/powerpc/include/asm/cacheflush.h |  1 +
>   arch/powerpc/lib/pmem.c               | 50 ++++++++++++++++++++++++---
>   2 files changed, 47 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/cacheflush.h b/arch/powerpc/include/asm/cacheflush.h
> index de600b915a3c..54764c6e922d 100644
> --- a/arch/powerpc/include/asm/cacheflush.h
> +++ b/arch/powerpc/include/asm/cacheflush.h
> @@ -6,6 +6,7 @@
>   
>   #include <linux/mm.h>
>   #include <asm/cputable.h>
> +#include <asm/cpu_has_feature.h>
>   
>   #ifdef CONFIG_PPC_BOOK3S_64
>   /*
> diff --git a/arch/powerpc/lib/pmem.c b/arch/powerpc/lib/pmem.c
> index 0666a8d29596..5a61aaeb6930 100644
> --- a/arch/powerpc/lib/pmem.c
> +++ b/arch/powerpc/lib/pmem.c
> @@ -9,20 +9,62 @@
>   
>   #include <asm/cacheflush.h>
>   
> +static inline void __clean_pmem_range(unsigned long start, unsigned long stop)
> +{
> +	unsigned long shift = l1_dcache_shift();
> +	unsigned long bytes = l1_dcache_bytes();
> +	void *addr = (void *)(start & ~(bytes - 1));
> +	unsigned long size = stop - (unsigned long)addr + (bytes - 1);
> +	unsigned long i;
> +
> +	for (i = 0; i < size >> shift; i++, addr += bytes)
> +		asm volatile(PPC_DCBSTPS(%0, %1): :"i"(0), "r"(addr): "memory");
> +
> +
> +	asm volatile(PPC_PHWSYNC ::: "memory");
> +}
> +
> +static inline void __flush_pmem_range(unsigned long start, unsigned long stop)
> +{
> +	unsigned long shift = l1_dcache_shift();
> +	unsigned long bytes = l1_dcache_bytes();
> +	void *addr = (void *)(start & ~(bytes - 1));
> +	unsigned long size = stop - (unsigned long)addr + (bytes - 1);
> +	unsigned long i;
> +
> +	for (i = 0; i < size >> shift; i++, addr += bytes)
> +		asm volatile(PPC_DCBFPS(%0, %1): :"i"(0), "r"(addr): "memory");
> +
> +
> +	asm volatile(PPC_PHWSYNC ::: "memory");
> +}
> +
> +static inline void clean_pmem_range(unsigned long start, unsigned long stop)
> +{
> +	if (cpu_has_feature(CPU_FTR_ARCH_207S))
> +		return __clean_pmem_range(start, stop);
> +}
> +
> +static inline void flush_pmem_range(unsigned long start, unsigned long stop)
> +{
> +	if (cpu_has_feature(CPU_FTR_ARCH_207S))
> +		return __flush_pmem_range(start, stop);
> +}
> +
>   /*
>    * CONFIG_ARCH_HAS_PMEM_API symbols
>    */
>   void arch_wb_cache_pmem(void *addr, size_t size)
>   {
>   	unsigned long start = (unsigned long) addr;
> -	flush_dcache_range(start, start + size);
> +	clean_pmem_range(start, start + size);
>   }
>   EXPORT_SYMBOL_GPL(arch_wb_cache_pmem);
>   
>   void arch_invalidate_pmem(void *addr, size_t size)
>   {
>   	unsigned long start = (unsigned long) addr;
> -	flush_dcache_range(start, start + size);
> +	flush_pmem_range(start, start + size);
>   }
>   EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
>   
> @@ -35,7 +77,7 @@ long __copy_from_user_flushcache(void *dest, const void __user *src,
>   	unsigned long copied, start = (unsigned long) dest;
>   
>   	copied = __copy_from_user(dest, src, size);
> -	flush_dcache_range(start, start + size);
> +	clean_pmem_range(start, start + size);
>   
>   	return copied;
>   }
> @@ -45,7 +87,7 @@ void *memcpy_flushcache(void *dest, const void *src, size_t size)
>   	unsigned long start = (unsigned long) dest;
>   
>   	memcpy(dest, src, size);
> -	flush_dcache_range(start, start + size);
> +	clean_pmem_range(start, start + size);
>   
>   	return dest;
>   }