Bump. Any comments? I think there is a real issue here so I'd like some confirmation on that at least. On Fri, Jun 7, 2013 at 10:23 AM, Myron Stowe <myron.stowe@xxxxxxxxxx> wrote: > While the megaraid device itself may be 64-bit DMA capable, 32-bit address > restricted DMA buffers are apparently required for "internal commands" as > is denoted by a couple of comments - "For all internal commands, the > buffer must be allocated in <4GB address range" - within the driver. > > If the device is 64-bit DMA capable then, once it is setup, any subsequent > DMA allocations for "internal commands" would not be properly restricted > due to megaraid_probe_one() having called pci_set_dma_mask() on pdev with > DMA_BIT_MASK(64). The driver attempts to solve this by using > make_local_pdev() to dynamically create local pci_dev structures which are > then set and used for allocating 32-bit address space restricted DMA > buffers[1] but I don't believe that the implementation works as intended. > > > Assume that the megaraid device is 64-bit DMA capable. While probing the > device and attaching the megaraid driver, pci_set_dma_mask() is called > with the "originating pdev" and a DMA_BIT_MASK of 64. As a result, any > subsequent dynamic DMA related allocations associated with the > "originating pdev" will acquire 64-bit based buffers, which do not meet > the addressing restrictions for internal commands. > > megaraid_probe_one(struct pci_dev *pdev, ...) > ... > pci_set_dma_mask(pdev, DMA_BIT_MASK(64)); > > As mentioned, the driver attempts to solve this by using make_local_pdev() > to dynamically create local pci_dev structures - "local pdev's" - which > are set with a DMA_BIT_MASK of 32. > > make_local_pdev > alloc_pci_dev > memcpy > pci_set_dma_mask > dma_set_mask > *dev->dma_mask = mask; > > The "local pdev" is then used in allocating a DMA buffer in an attempt to > meet the < 4 GB restriction. > > For a 64-bit DMA capable device, the "originating pdev" will have its > 'dma_mask' set to 0xffffffffffffffff after the driver attaches. > Subsequently, when an internal command is initiated, make_local_pdev() is > called. make_local_pdev() uses the PCI's core to allocate a "local pdev" > and then copies the "originating pdev" content into the newly allocated > "local pdev". As a result of copying the "originating pdev" content into > the "local pdev", pdev->dev.dma_mask will be pointing back to the > "originating pdev's" 'dma_mask' member, not the "local pdev's" as > intended. Thus, when make_local_pdev() calls pci_set_dma_mask() in an > attempt to set the "local pdev's" DMA mask to 32 it will instead overwrite > the "originating pdev's" DMA mask. Thus, after any user initiated > commands are issued, all subsequent DMA allocations will be 32-bit > restricted from that point onward regardless of whether they are internal > commands or otherwise. > > > This patch fixes the issue by removing the setup of DMA_BIT_MASK to 64 in > megaraid_probe_one(), leaving the driver with default 32-bit DMA > capabilities, as it currently ends up in such a state anyway after any > internal commands are initiated. > > > [1] It seems strange that both mega_buffer/buf_dma_handle and > make_local_pdev() both exist for internal commands but this has been > the case for a long time - at least since 2.6.12-rc2. Perhaps there > is some coalescing that could be done. > --- > > Myron Stowe (3): > [SCSI] megaraid: Remove 64-bit DMA related dead code > [SCSI] megaraid: Remove local (struct pci_dev) pdev's > [SCSI] megaraid: Remove 64-bit DMA_BIT_MASK capability > > > drivers/scsi/megaraid.c | 152 ++++++++--------------------------------------- > drivers/scsi/megaraid.h | 1 > 2 files changed, 27 insertions(+), 126 deletions(-) > > -- > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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
