[PATCH] Possible fix to recent data corruption on HEAD since USB2

Due to some good sleuthing by avg_at_, there is a patch that might fix the recent 
reports of data corruption on current.  It would explain some of the recent 
reports where a file that was read would have missing gaps of bytes.  The 
problem is with the BUS_DMA_KEEP_PG_OFFSET changes to bus_dma.  When a bounce 
page was used by USB2, the changes to bus_dma would actually change the 
starting virtual and physical addresses of the bounce page.  When the bounce 
page was no longer needed it was left in this bogus state.  Later if another 
device used the same bounce page for DMA it would use the wrong offset and 
address.  The issue there is if the second device was doing a full page of 
I/O.  In that case the DMA from the device would actually spill over into the 
next page which could in theory be used by another DMA request.  It could 
also break alignment assumptions (since the previous PG_OFFSET may not be 
aligned and the bus_dma code assumes bounce pages for the !PG_OFFSET case are 
page aligned).  The quick fix is to always restore the bounce page to the 
normal state when a PG_OFFSET DMA request is finished.   I'd actually prefer 
not ever touching the page's starting addresses, but those changes would be 
more invasive I believe.

http://www.FreeBSD.org/~jhb/patches/dma_sg.patch

Index: amd64/amd64/busdma_machdep.c
===================================================================
--- amd64/amd64/busdma_machdep.c	(revision 191101)
+++ amd64/amd64/busdma_machdep.c	(working copy)
_at__at_ -1138,8 +1138,6 _at__at_
 
 	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
 		/* page offset needs to be preserved */
-		bpage->vaddr &= ~PAGE_MASK;
-		bpage->busaddr &= ~PAGE_MASK;
 		bpage->vaddr |= vaddr & PAGE_MASK;
 		bpage->busaddr |= vaddr & PAGE_MASK;
 	}
_at__at_ -1158,6 +1156,10 _at__at_
 	bz = dmat->bounce_zone;
 	bpage->datavaddr = 0;
 	bpage->datacount = 0;
+	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
+		bpage->vaddr &= ~PAGE_MASK;
+		bpage->busaddr &= ~PAGE_MASK;
+	}
 
 	mtx_lock(&bounce_lock);
 	STAILQ_INSERT_HEAD(&bz->bounce_page_list, bpage, links);
Index: arm/arm/busdma_machdep.c
===================================================================
--- arm/arm/busdma_machdep.c	(revision 191101)
+++ arm/arm/busdma_machdep.c	(working copy)
_at__at_ -1428,8 +1428,6 _at__at_
 
 	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
 		/* page offset needs to be preserved */
-		bpage->vaddr &= ~PAGE_MASK;
-		bpage->busaddr &= ~PAGE_MASK;
 		bpage->vaddr |= vaddr & PAGE_MASK;
 		bpage->busaddr |= vaddr & PAGE_MASK;
 	}
_at__at_ -1448,6 +1446,10 _at__at_
 	bz = dmat->bounce_zone;
 	bpage->datavaddr = 0;
 	bpage->datacount = 0;
+	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
+		bpage->vaddr &= ~PAGE_MASK;
+		bpage->busaddr &= ~PAGE_MASK;
+	}
 
 	mtx_lock(&bounce_lock);
 	STAILQ_INSERT_HEAD(&bz->bounce_page_list, bpage, links);
Index: i386/i386/busdma_machdep.c
===================================================================
--- i386/i386/busdma_machdep.c	(revision 191101)
+++ i386/i386/busdma_machdep.c	(working copy)
_at__at_ -1156,8 +1156,6 _at__at_
 
 	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
 		/* page offset needs to be preserved */
-		bpage->vaddr &= ~PAGE_MASK;
-		bpage->busaddr &= ~PAGE_MASK;
 		bpage->vaddr |= vaddr & PAGE_MASK;
 		bpage->busaddr |= vaddr & PAGE_MASK;
 	}
_at__at_ -1176,6 +1174,10 _at__at_
 	bz = dmat->bounce_zone;
 	bpage->datavaddr = 0;
 	bpage->datacount = 0;
+	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
+		bpage->vaddr &= ~PAGE_MASK;
+		bpage->busaddr &= ~PAGE_MASK;
+	}
 
 	mtx_lock(&bounce_lock);
 	STAILQ_INSERT_HEAD(&bz->bounce_page_list, bpage, links);
Index: ia64/ia64/busdma_machdep.c
===================================================================
--- ia64/ia64/busdma_machdep.c	(revision 191101)
+++ ia64/ia64/busdma_machdep.c	(working copy)
_at__at_ -941,8 +941,6 _at__at_
 
 	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
 		/* page offset needs to be preserved */
-		bpage->vaddr &= ~PAGE_MASK;
-		bpage->busaddr &= ~PAGE_MASK;
 		bpage->vaddr |= vaddr & PAGE_MASK;
 		bpage->busaddr |= vaddr & PAGE_MASK;
 	}
_at__at_ -959,6 +957,10 _at__at_
 
 	bpage->datavaddr = 0;
 	bpage->datacount = 0;
+	if (dmat->flags & BUS_DMA_KEEP_PG_OFFSET) {
+		bpage->vaddr &= ~PAGE_MASK;
+		bpage->busaddr &= ~PAGE_MASK;
+	}
 
 	mtx_lock(&bounce_lock);
 	STAILQ_INSERT_HEAD(&bounce_page_list, bpage, links);

-- 
John Baldwin