arm/160431: [busdma] [patch] Disable interrupts during busdma cache sync operations.

[Ian Lepore]

The following reply was made to PR arm/160431; it has been noted by GNATS.

From: Ian Lepore <freebsd at damnhippie.dyndns.org>
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: arm/160431: [busdma] [patch] Disable interrupts during busdma
 cache sync operations.
Date: Sat, 21 Apr 2012 10:22:47 -0600

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 Arrgh!  One more time, with the actual correct patch attached (and this
 time validated correctly by building kernel rather than world, doh!).
 
 
 
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 Index: sys/arm/arm/busdma_machdep.c
 ===================================================================
 --- sys/arm/arm/busdma_machdep.c	(revision 234543)
 +++ sys/arm/arm/busdma_machdep.c	(working copy)
 @@ -1090,6 +1090,8 @@
  static void
  bus_dmamap_sync_buf(void *buf, int len, bus_dmasync_op_t op)
  {
 +	uint32_t intr;
 +	int partial; 
  	char _tmp_cl[arm_dcache_align], _tmp_clend[arm_dcache_align];
  
  	if ((op & BUS_DMASYNC_PREWRITE) && !(op & BUS_DMASYNC_PREREAD)) {
 @@ -1106,28 +1108,45 @@
  	    		cpu_l2cache_wbinv_range((vm_offset_t)buf, len);
  		}
  	}
 +	/*
 +	 * Interrupts must be disabled while handling a partial cacheline flush,
 +	 * otherwise the interrupt handling code could modify data in the
 +	 * non-DMA part of a cacheline while we have it stashed away in the
 +	 * temporary stack buffer, then we end up restoring the stale value.
 +	 * As unlikely as this seems, it has been observed in the real world.
 +	 */
  	if (op & BUS_DMASYNC_POSTREAD) {
 -		if ((vm_offset_t)buf & arm_dcache_align_mask) {
 -			memcpy(_tmp_cl, (void *)((vm_offset_t)buf & ~
 -			    arm_dcache_align_mask),
 -			    (vm_offset_t)buf & arm_dcache_align_mask);
 +		partial = (((vm_offset_t)buf) | len) & arm_dcache_align_mask;
 +		if (partial) {
 +			intr = intr_disable();
 +			if ((vm_offset_t)buf & arm_dcache_align_mask) {
 +				memcpy(_tmp_cl, (void *)((vm_offset_t)buf &
 +				    ~arm_dcache_align_mask),
 +				    (vm_offset_t)buf & arm_dcache_align_mask);
 +			}
 +			if (((vm_offset_t)buf + len) & arm_dcache_align_mask) {
 +				memcpy(_tmp_clend, 
 +				    (void *)((vm_offset_t)buf + len),
 +				    arm_dcache_align - 
 +				    (((vm_offset_t)(buf) + len) &
 +				    arm_dcache_align_mask));
 +			}
  		}
 -		if (((vm_offset_t)buf + len) & arm_dcache_align_mask) {
 -			memcpy(_tmp_clend, (void *)((vm_offset_t)buf + len),
 -			    arm_dcache_align - (((vm_offset_t)(buf) + len) &
 -			   arm_dcache_align_mask));
 -		}
  		cpu_dcache_inv_range((vm_offset_t)buf, len);
  		cpu_l2cache_inv_range((vm_offset_t)buf, len);
 -
 -		if ((vm_offset_t)buf & arm_dcache_align_mask)
 -			memcpy((void *)((vm_offset_t)buf &
 -			    ~arm_dcache_align_mask), _tmp_cl, 
 -			    (vm_offset_t)buf & arm_dcache_align_mask);
 -		if (((vm_offset_t)buf + len) & arm_dcache_align_mask)
 -			memcpy((void *)((vm_offset_t)buf + len), _tmp_clend,
 -			    arm_dcache_align - (((vm_offset_t)(buf) + len) &
 -			   arm_dcache_align_mask));
 +		if (partial) {
 +			if ((vm_offset_t)buf & arm_dcache_align_mask)
 +				memcpy((void *)((vm_offset_t)buf &
 +				    ~arm_dcache_align_mask), _tmp_cl, 
 +				    (vm_offset_t)buf & arm_dcache_align_mask);
 +			if (((vm_offset_t)buf + len) & arm_dcache_align_mask)
 +				memcpy((void *)((vm_offset_t)buf + len), 
 +				    _tmp_clend,
 +				    arm_dcache_align - 
 +				    (((vm_offset_t)(buf) + len) &
 +				    arm_dcache_align_mask));
 +			intr_restore(intr);
 +		}
  	}
  }
  
 
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