On Wed, 16 Jul 2008 14:02:27 -0400 (EDT) Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > On Wed, 16 Jul 2008, FUJITA Tomonori wrote: > > > On Tue, 15 Jul 2008 11:46:46 -0400 (EDT) > > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > > > >> Even if we fix it now, the question is: how long it will stay fixed? Until > > > >> someone makes another change to struct device that restricts boundaries on > > > >> some wacky hardware. > > > > > > > > I'm not sure how the boundary restriction of a device can break > > > > the VMERGE accounting. > > > > > > Because block layer code doesn't know anything about the device, pci > > > access restrictions and so on. > > > > Not true, the block layer knows about the device restrictions like DMA > > boundary. > > > > But it's not the point here because the boundary restriction doesn't > > matter for the VMERGE accounting. An IOMMU just returns an error if it > > can't allocate an I/O space fit for the device restrictions. > > > > > > Please give me an example how the boundary restriction of a device can > > break the VMERGE accounting and an IOMMU if you aren't still sure. > > You have dma_get_seg_boundary and dma_get_max_seg_size. On sparc64, adding > one of these broken VMERGE accounting (the VMERGE didn't happen past 64-kb > boundary and bio layer thought that VMERGE would be possible). If the device has 64KB boundary restriction, the device also has max_seg_size restriction of 64KB or under. So the vmerge acounting works (though we need to fix it to handle max_seg_size, as discussed). > And if you fix this case, someone will break it again, sooner or later, by > adding new restriction. What is your new restriction? All restrictions that IOMMUs need to know are dma_get_seg_boundary and dma_get_max_seg_size. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
