Message-ID: <8a86bccf-ae4d-6d2c-72b1-db136cec9d10@c-s.fr>
Date:   Thu, 15 Aug 2019 09:29:37 +0200
From:   christophe leroy <christophe.leroy@....fr>
To:     Alastair D'Silva <alastair@....ibm.com>, alastair@...ilva.org
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>, Qian Cai <cai@....pw>,
        Nicholas Piggin <npiggin@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Allison Randal <allison@...utok.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] powerpc: Convert flush_icache_range & friends to C



Le 15/08/2019 à 06:10, Alastair D'Silva a écrit :
> From: Alastair D'Silva <alastair@...ilva.org>
> 
> Similar to commit 22e9c88d486a
> ("powerpc/64: reuse PPC32 static inline flush_dcache_range()")
> this patch converts flush_icache_range() to C, and reimplements the
> following functions as wrappers around it:
> __flush_dcache_icache
> __flush_dcache_icache_phys

Not sure you can do that for __flush_dcache_icache_phys(), see detailed 
comments below

> 
> This was done as we discovered a long-standing bug where the length of the
> range was truncated due to using a 32 bit shift instead of a 64 bit one.
> 
> By converting these functions to C, it becomes easier to maintain.
> 
> Signed-off-by: Alastair D'Silva <alastair@...ilva.org>
> ---
>   arch/powerpc/include/asm/cache.h      |  26 +++---
>   arch/powerpc/include/asm/cacheflush.h |  32 ++++---
>   arch/powerpc/kernel/misc_32.S         | 117 --------------------------
>   arch/powerpc/kernel/misc_64.S         |  97 ---------------------
>   arch/powerpc/mm/mem.c                 |  71 +++++++++++++++-
>   5 files changed, 102 insertions(+), 241 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/cache.h b/arch/powerpc/include/asm/cache.h
> index f852d5cd746c..728f154204db 100644
> --- a/arch/powerpc/include/asm/cache.h
> +++ b/arch/powerpc/include/asm/cache.h
> @@ -98,20 +98,7 @@ static inline u32 l1_icache_bytes(void)
>   #endif
>   #endif /* ! __ASSEMBLY__ */
>   
> -#if defined(__ASSEMBLY__)
> -/*
> - * For a snooping icache, we still need a dummy icbi to purge all the
> - * prefetched instructions from the ifetch buffers. We also need a sync
> - * before the icbi to order the the actual stores to memory that might
> - * have modified instructions with the icbi.
> - */
> -#define PURGE_PREFETCHED_INS	\
> -	sync;			\
> -	icbi	0,r3;		\
> -	sync;			\
> -	isync

Is this still used anywhere now ?

> -
> -#else
> +#if !defined(__ASSEMBLY__)
>   #define __read_mostly __attribute__((__section__(".data..read_mostly")))
>   
>   #ifdef CONFIG_PPC_BOOK3S_32
> @@ -145,6 +132,17 @@ static inline void dcbst(void *addr)
>   {
>   	__asm__ __volatile__ ("dcbst %y0" : : "Z"(*(u8 *)addr) : "memory");
>   }
> +
> +static inline void icbi(void *addr)
> +{
> +	__asm__ __volatile__ ("icbi 0, %0" : : "r"(addr) : "memory");
> +}
> +
> +static inline void iccci(void)
> +{
> +	__asm__ __volatile__ ("iccci 0, r0");

I think you need the "memory" clobber too here.

> +}
> +
>   #endif /* !__ASSEMBLY__ */
>   #endif /* __KERNEL__ */
>   #endif /* _ASM_POWERPC_CACHE_H */
> diff --git a/arch/powerpc/include/asm/cacheflush.h b/arch/powerpc/include/asm/cacheflush.h
> index ed57843ef452..4c3377aff8ed 100644
> --- a/arch/powerpc/include/asm/cacheflush.h
> +++ b/arch/powerpc/include/asm/cacheflush.h
> @@ -42,24 +42,18 @@ extern void flush_dcache_page(struct page *page);
>   #define flush_dcache_mmap_lock(mapping)		do { } while (0)
>   #define flush_dcache_mmap_unlock(mapping)	do { } while (0)
>   
> -extern void flush_icache_range(unsigned long, unsigned long);
> +void flush_icache_range(unsigned long start, unsigned long stop);
>   extern void flush_icache_user_range(struct vm_area_struct *vma,
>   				    struct page *page, unsigned long addr,
>   				    int len);
> -extern void __flush_dcache_icache(void *page_va);
>   extern void flush_dcache_icache_page(struct page *page);
> -#if defined(CONFIG_PPC32) && !defined(CONFIG_BOOKE)
> -extern void __flush_dcache_icache_phys(unsigned long physaddr);
> -#else
> -static inline void __flush_dcache_icache_phys(unsigned long physaddr)
> -{
> -	BUG();
> -}
> -#endif
>   
> -/*
> - * Write any modified data cache blocks out to memory and invalidate them.
> +/**
> + * flush_dcache_range(): Write any modified data cache blocks out to memory and invalidate them.
>    * Does not invalidate the corresponding instruction cache blocks.
> + *
> + * @start: the start address
> + * @stop: the stop address (exclusive)
>    */
>   static inline void flush_dcache_range(unsigned long start, unsigned long stop)
>   {
> @@ -82,6 +76,20 @@ static inline void flush_dcache_range(unsigned long start, unsigned long stop)
>   		isync();
>   }
>   
> +/**
> + * __flush_dcache_icache(): Flush a particular page from the data cache to RAM.
> + * Note: this is necessary because the instruction cache does *not*
> + * snoop from the data cache.
> + *
> + * @page: the address of the page to flush
> + */
> +static inline void __flush_dcache_icache(void *page)
> +{
> +	unsigned long page_addr = (unsigned long)page;

The function is small enough to call this addr instead of page_addr 
without ambiguity.

> +
> +	flush_icache_range(page_addr, page_addr + PAGE_SIZE);

Finally, I think that's not so simple. For the 44x, if MMU_FTR_TYPE_44x 
is set, that's just a clean_dcache_range().
If that feature is not set, it looks like a standard 
flush_icache_range() but without the special CONFIG_4xx handling with 
iccci we have in flush_icache_range()

> +}
> +
>   /*
>    * Write any modified data cache blocks out to memory.
>    * Does not invalidate the corresponding cache lines (especially for
> diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
> index fe4bd321730e..12b95e6799d4 100644
> --- a/arch/powerpc/kernel/misc_32.S
> +++ b/arch/powerpc/kernel/misc_32.S
> @@ -318,123 +318,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_UNIFIED_ID_CACHE)
>   EXPORT_SYMBOL(flush_instruction_cache)
>   #endif /* CONFIG_PPC_8xx */
>   
> -/*
> - * Write any modified data cache blocks out to memory
> - * and invalidate the corresponding instruction cache blocks.
> - * This is a no-op on the 601.
> - *
> - * flush_icache_range(unsigned long start, unsigned long stop)
> - */
> -_GLOBAL(flush_icache_range)
> -BEGIN_FTR_SECTION
> -	PURGE_PREFETCHED_INS
> -	blr				/* for 601, do nothing */
> -END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> -	rlwinm	r3,r3,0,0,31 - L1_CACHE_SHIFT
> -	subf	r4,r3,r4
> -	addi	r4,r4,L1_CACHE_BYTES - 1
> -	srwi.	r4,r4,L1_CACHE_SHIFT
> -	beqlr
> -	mtctr	r4
> -	mr	r6,r3
> -1:	dcbst	0,r3
> -	addi	r3,r3,L1_CACHE_BYTES
> -	bdnz	1b
> -	sync				/* wait for dcbst's to get to ram */
> -#ifndef CONFIG_44x
> -	mtctr	r4
> -2:	icbi	0,r6
> -	addi	r6,r6,L1_CACHE_BYTES
> -	bdnz	2b
> -#else
> -	/* Flash invalidate on 44x because we are passed kmapped addresses and
> -	   this doesn't work for userspace pages due to the virtually tagged
> -	   icache.  Sigh. */
> -	iccci	0, r0
> -#endif
> -	sync				/* additional sync needed on g4 */
> -	isync
> -	blr
> -_ASM_NOKPROBE_SYMBOL(flush_icache_range)
> -EXPORT_SYMBOL(flush_icache_range)
> -
> -/*
> - * Flush a particular page from the data cache to RAM.
> - * Note: this is necessary because the instruction cache does *not*
> - * snoop from the data cache.
> - * This is a no-op on the 601 which has a unified cache.
> - *
> - *	void __flush_dcache_icache(void *page)
> - */
> -_GLOBAL(__flush_dcache_icache)
> -BEGIN_FTR_SECTION
> -	PURGE_PREFETCHED_INS
> -	blr
> -END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> -	rlwinm	r3,r3,0,0,31-PAGE_SHIFT		/* Get page base address */
> -	li	r4,PAGE_SIZE/L1_CACHE_BYTES	/* Number of lines in a page */
> -	mtctr	r4
> -	mr	r6,r3
> -0:	dcbst	0,r3				/* Write line to ram */
> -	addi	r3,r3,L1_CACHE_BYTES
> -	bdnz	0b
> -	sync
> -#ifdef CONFIG_44x
> -	/* We don't flush the icache on 44x. Those have a virtual icache
> -	 * and we don't have access to the virtual address here (it's
> -	 * not the page vaddr but where it's mapped in user space). The
> -	 * flushing of the icache on these is handled elsewhere, when
> -	 * a change in the address space occurs, before returning to
> -	 * user space
> -	 */
> -BEGIN_MMU_FTR_SECTION
> -	blr
> -END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_44x)
> -#endif /* CONFIG_44x */
> -	mtctr	r4
> -1:	icbi	0,r6
> -	addi	r6,r6,L1_CACHE_BYTES
> -	bdnz	1b
> -	sync
> -	isync
> -	blr
> -
> -#ifndef CONFIG_BOOKE
> -/*
> - * Flush a particular page from the data cache to RAM, identified
> - * by its physical address.  We turn off the MMU so we can just use
> - * the physical address (this may be a highmem page without a kernel
> - * mapping).
> - *
> - *	void __flush_dcache_icache_phys(unsigned long physaddr)
> - */
> -_GLOBAL(__flush_dcache_icache_phys)
> -BEGIN_FTR_SECTION
> -	PURGE_PREFETCHED_INS
> -	blr					/* for 601, do nothing */
> -END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> -	mfmsr	r10
> -	rlwinm	r0,r10,0,28,26			/* clear DR */
> -	mtmsr	r0
> -	isync
> -	rlwinm	r3,r3,0,0,31-PAGE_SHIFT		/* Get page base address */
> -	li	r4,PAGE_SIZE/L1_CACHE_BYTES	/* Number of lines in a page */
> -	mtctr	r4
> -	mr	r6,r3
> -0:	dcbst	0,r3				/* Write line to ram */
> -	addi	r3,r3,L1_CACHE_BYTES
> -	bdnz	0b
> -	sync
> -	mtctr	r4
> -1:	icbi	0,r6
> -	addi	r6,r6,L1_CACHE_BYTES
> -	bdnz	1b
> -	sync
> -	mtmsr	r10				/* restore DR */
> -	isync
> -	blr
> -#endif /* CONFIG_BOOKE */
> -
>   /*
>    * Copy a whole page.  We use the dcbz instruction on the destination
>    * to reduce memory traffic (it eliminates the unnecessary reads of
> diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
> index 9bc0aa9aeb65..fa451186620f 100644
> --- a/arch/powerpc/kernel/misc_64.S
> +++ b/arch/powerpc/kernel/misc_64.S
> @@ -54,103 +54,6 @@ PPC64_CACHES:
>   	.tc		ppc64_caches[TC],ppc64_caches
>   	.section	".text"

Is the above still needed at all once all cache functions are gone ?

>   
> -/*
> - * Write any modified data cache blocks out to memory
> - * and invalidate the corresponding instruction cache blocks.
> - *
> - * flush_icache_range(unsigned long start, unsigned long stop)
> - *
> - *   flush all bytes from start through stop-1 inclusive
> - */
> -
> -_GLOBAL_TOC(flush_icache_range)
> -BEGIN_FTR_SECTION
> -	PURGE_PREFETCHED_INS
> -	blr
> -END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> -/*
> - * Flush the data cache to memory
> - *
> - * Different systems have different cache line sizes
> - * and in some cases i-cache and d-cache line sizes differ from
> - * each other.
> - */
> - 	ld	r10,PPC64_CACHES@toc(r2)
> -	lwz	r7,DCACHEL1BLOCKSIZE(r10)/* Get cache block size */
> -	addi	r5,r7,-1
> -	andc	r6,r3,r5		/* round low to line bdy */
> -	subf	r8,r6,r4		/* compute length */
> -	add	r8,r8,r5		/* ensure we get enough */
> -	lwz	r9,DCACHEL1LOGBLOCKSIZE(r10)	/* Get log-2 of cache block size */
> -	srd.	r8,r8,r9		/* compute line count */
> -	beqlr				/* nothing to do? */
> -	mtctr	r8
> -1:	dcbst	0,r6
> -	add	r6,r6,r7
> -	bdnz	1b
> -	sync
> -
> -/* Now invalidate the instruction cache */
> -	
> -	lwz	r7,ICACHEL1BLOCKSIZE(r10)	/* Get Icache block size */
> -	addi	r5,r7,-1
> -	andc	r6,r3,r5		/* round low to line bdy */
> -	subf	r8,r6,r4		/* compute length */
> -	add	r8,r8,r5
> -	lwz	r9,ICACHEL1LOGBLOCKSIZE(r10)	/* Get log-2 of Icache block size */
> -	srd.	r8,r8,r9		/* compute line count */
> -	beqlr				/* nothing to do? */
> -	mtctr	r8
> -2:	icbi	0,r6
> -	add	r6,r6,r7
> -	bdnz	2b
> -	isync
> -	blr
> -_ASM_NOKPROBE_SYMBOL(flush_icache_range)
> -EXPORT_SYMBOL(flush_icache_range)
> -
> -/*
> - * Flush a particular page from the data cache to RAM.
> - * Note: this is necessary because the instruction cache does *not*
> - * snoop from the data cache.
> - *
> - *	void __flush_dcache_icache(void *page)
> - */
> -_GLOBAL(__flush_dcache_icache)
> -/*
> - * Flush the data cache to memory
> - *
> - * Different systems have different cache line sizes
> - */
> -
> -BEGIN_FTR_SECTION
> -	PURGE_PREFETCHED_INS
> -	blr
> -END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> -
> -/* Flush the dcache */
> - 	ld	r7,PPC64_CACHES@toc(r2)
> -	clrrdi	r3,r3,PAGE_SHIFT           	    /* Page align */
> -	lwz	r4,DCACHEL1BLOCKSPERPAGE(r7)	/* Get # dcache blocks per page */
> -	lwz	r5,DCACHEL1BLOCKSIZE(r7)	/* Get dcache block size */
> -	mr	r6,r3
> -	mtctr	r4
> -0:	dcbst	0,r6
> -	add	r6,r6,r5
> -	bdnz	0b
> -	sync
> -
> -/* Now invalidate the icache */	
> -
> -	lwz	r4,ICACHEL1BLOCKSPERPAGE(r7)	/* Get # icache blocks per page */
> -	lwz	r5,ICACHEL1BLOCKSIZE(r7)	/* Get icache block size */
> -	mtctr	r4
> -1:	icbi	0,r3
> -	add	r3,r3,r5
> -	bdnz	1b
> -	isync
> -	blr
> -
>   _GLOBAL(__bswapdi2)
>   EXPORT_SYMBOL(__bswapdi2)
>   	srdi	r8,r3,32
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 9191a66b3bc5..5400da87a804 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -321,6 +321,66 @@ void free_initmem(void)
>   	free_initmem_default(POISON_FREE_INITMEM);
>   }
>   
> +/**
> + * flush_icache_range: Write any modified data cache blocks out to memory
> + * and invalidate the corresponding blocks in the instruction cache
> + *
> + * Generic code will call this after writing memory, before executing from it.
> + *
> + * @start: the start address
> + * @stop: the stop address (exclusive)
> + */
> +void flush_icache_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;
> +
> +	if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) {
> +		/* For a snooping icache, we still need a dummy icbi to purge all the
> +		 * prefetched instructions from the ifetch buffers. We also need a sync
> +		 * before the icbi to order the the actual stores to memory that might
> +		 * have modified instructions with the icbi.
> +		 */
> +		mb(); /* sync */
> +		icbi((void *)start);
> +		mb(); /* sync */
> +		isync();
> +		return;
> +	}
> +
> +	/* Flush the data cache to memory */
> +	for (i = 0; i < size >> shift; i++, addr += bytes)
> +		dcbst(addr);
> +
> +	mb();	/* sync */

Can we call clean_dcache_range() here instead ?

> +
> +#ifdef CONFIG_44x

Could we use the following instead of an #ifdef#else#endif ?

if (IS_ENABLED(CONFIG_44x)) {
} else {
}

> +	/* Flash invalidate on 44x because we are passed kmapped addresses and
> +	 * this doesn't work for userspace pages due to the virtually tagged
> +	 * icache.
> +	 */
> +
> +	iccci();
> +#else
> +	shift = l1_icache_shift();
> +	bytes = l1_icache_bytes();
> +	addr = (void *)(start & ~(bytes - 1));
> +	size = stop - (unsigned long)addr + (bytes - 1);
> +
> +	/* Now invalidate the instruction cache */
> +	for (i = 0; i < size >> shift; i++, addr += bytes)
> +		icbi(addr);
> +#endif
> +
> +	if (!IS_ENABLED(CONFIG_PPC64))
> +		mb(); /* additional sync needed on g4 */
> +	isync();
> +}
> +EXPORT_SYMBOL(flush_icache_range);
> +
>   /*
>    * This is called when a page has been modified by the kernel.
>    * It just marks the page as not i-cache clean.  We do the i-cache
> @@ -353,7 +413,16 @@ void flush_dcache_icache_page(struct page *page)
>   		__flush_dcache_icache(start);
>   		kunmap_atomic(start);
>   	} else {
> -		__flush_dcache_icache_phys(page_to_pfn(page) << PAGE_SHIFT);
> +		unsigned long msr = mfmsr();
> +
> +		/* Clear the DR bit so that we operate on physical
> +		 * rather than virtual addresses
> +		 */
> +		mtmsr(msr & ~(MSR_DR));
> +
> +		__flush_dcache_icache((void *)physaddr);
> +
> +		mtmsr(msr);

You can't do that I think. Once Data MMU is deactivated, you really have 
to take can of what data you access. For instance, the C code can't use 
stack anymore, neither can it directly use any global var. Only vars 
that are in registers can safely be used. As it can't use the stack, it 
is likely that it can't call another function in general case. So I 
don't think we can write in C a function which needs to de-activate data 
MMU.
I think this function must remain in ASM.

And what happened to the following that was around 
__flush_dcache_icache_phys() in asm/cacheflush.h ?

#if defined(CONFIG_PPC32) && !defined(CONFIG_BOOKE)
...
#else
BUG();
#endif

>   	}
>   #endif
>   }
> 

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