Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
On Sat, Jun 15, 2013 at 9:10 PM, Jussi Kivilinna wrote: > On 15.06.2013 15:07, Ming Lei wrote: >> On Sat, Jun 15, 2013 at 6:19 PM, Jussi Kivilinna >> wrote: >>> On 15.06.2013 10:41, Ming Lei wrote: Cc: netdev On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna wrote: > Appearently some out-of-tree USB host drivers do not handle DMA alignment > for Looks these host drivers have to face the fact that the transfer buffer is often DMA non-aligned from network device drivers(in fact, the buffer is from network protocol stack), if you run usbnet, then you will get the added warning immediately. >>> >>> Yes, getting warning immediately, but once, and blaming host driver seems >>> ok. >> >> We do know the fact of non-aligned transfer buffer from network, which has >> been >> for long time, so does it make sense to print warning and annoy people? > > It's only printed if host controller driver is not behaving correctly. If you make sure the warning is only printed on broken controller, that is fine. > > I have changed the message to be printed for v2-patch, and it is now: > dev_WARN_ONCE(hcd->self.controller, 1, > "broken USB host controller driver; does not correctly handle DMA > alignment for urb->transfer_buffer (offset: %d).\n", > dma_offset); > > I sent the patch as RFC since I'm not sure.. maybe annoying warnings make That is fine. > people aware of issues that they don't yet know of and things get fixed? I mean it isn't good to annoy people who are using good host controller, :-) >> >>> > URB buffers and let core/hcd.c to do the mapping on architectures that > have > minimum DMA alignment requirements. This leads to random memory > corruptions > and crashes when using USB device drivers that use unaligned URB buffers. Maybe you should check the dma mapping/unmapping implementation of the arch, non-aligned buffer should have be covered by the API easily. Also USB Host controller should have supported non-aligned DMA buffer. >>> >>> From what I found, there was some discussion about these issues around 2010: >>> >>> http://lists.infradead.org/pipermail/linux-arm-kernel/2010-August/022983.html >> >> From the discussion, people think that HCD should handle the unaligned >> buffer, >> right? > > Yes, that's how I understood it. > >> >>> >>> To me, it seems that non-aligned buffers cannot be easily handled by all >>> archs >>> at dma mapping/unmapping phase and that HCD driver should do the alignment >>> on >> >> If the memory which shares cache line with transfer buffer can't be >> accessed during >> DMA transfer(between URB submit and complete), dma mapping/unmapping >> should have handled it. >> >> About the network transfer buffer case, I think it should be true, >> otherwise there >> should have lots of memory corruption reports about usb network drivers. >> Fortunately, there are seldom such reports. >> > > Another reason why rtl8192cu is so hard, is that it uses pre-allocated array > for buffers of multiple URBs, and more than one transfer buffer can reside on > same cache line. If so, that should be bug inside rtl8192, and more than one transfer buffer shares one cache line should be avoided, I understand the buffer isn't from network stack, don't I? > >>> archs that set ARCH_DMA_MINALIGN. For example, ehci_tegra does copy >>> unaligned >>> transfer buffers to temporary aligned buffers before letting them to USB >>> core. >> >> Yes, if host controller can't handle this, the HCD has to work around >> the problem. Anyway, most of host controllers can deal with the it, >> can't they? > > Can they? Maybe they can handle most cases of unaligned buffers, but not some > corner cases, like transfer buffers on same cache line. Of course, most of in-tree host controller can handle non-aligned buffer. If transfer buffers share one same cache line, it should be bug in driver, not fault of host controller. > >> >>> > > Instead of fixing host drivers, users end up posting bug reports against > those USB device drivers that use unaligned buffers for URB; such as with > rtl8192cu > (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). Not only rtl8192cu driver, all USB network device drivers have the problem. > > Patch makes this issue more visible at core level, and hopefully gives > hint > for future hcd driver implementors about this problem. So please find the root cause first, and don't add the noise now. >>> >>> I think the root cause is that host driver is letting pass non-aligned >>> buffers >>> to core on archs that have ARCH_DMA_MINALIGN set. >> >> No, I don't think so, about the problem, the dma alignment requirement should >> be from your host controller. >> >> As I said above, dma mapping/unmapping should be capable of dealing with >> the unaligned buffer if no one touch
Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
On 15.06.2013 16:10, Jussi Kivilinna wrote: [...] >> >>> > > Instead of fixing host drivers, users end up posting bug reports against > those USB device drivers that use unaligned buffers for URB; such as with > rtl8192cu > (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). Not only rtl8192cu driver, all USB network device drivers have the problem. > > Patch makes this issue more visible at core level, and hopefully gives > hint > for future hcd driver implementors about this problem. So please find the root cause first, and don't add the noise now. >>> >>> I think the root cause is that host driver is letting pass non-aligned >>> buffers >>> to core on archs that have ARCH_DMA_MINALIGN set. >> >> No, I don't think so, about the problem, the dma alignment requirement should >> be from your host controller. >> >> As I said above, dma mapping/unmapping should be capable of dealing with >> the unaligned buffer if no one touches memory which shares cacheline with >> URB->transfer_buffer during URB transfer. > > How can you guarantee that when you allow unaligned URB buffers? > > You can have the buffer as part of some larger structure and send out async > URB. > Then while buffer is DMA mapped and send async to hw, you use other parts of > that structure even if it shares cacheline with the buffer. You might issue > multiple URBs with transfer buffers within same cacheline. I would expect that > to be acceptable or URB documentation should say something against such. > Hm.. rethink this a bit. Transfer buffer might be dma aligned but shorter than cacheline and end of cacheline used as something else. Manual alignment by host driver does not catch that or fix that. So, yes.. dma mapping should work with unaligned buffers, but maybe the actual problem is multiple buffers from same cacheline. -Jussi -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
On 15.06.2013 15:07, Ming Lei wrote: > On Sat, Jun 15, 2013 at 6:19 PM, Jussi Kivilinna > wrote: >> On 15.06.2013 10:41, Ming Lei wrote: >>> Cc: netdev >>> >>> On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna >>> wrote: Appearently some out-of-tree USB host drivers do not handle DMA alignment for >>> >>> Looks these host drivers have to face the fact that the transfer buffer is >>> often >>> DMA non-aligned from network device drivers(in fact, the buffer is from >>> network protocol stack), if you run usbnet, then you will get the added >>> warning >>> immediately. >>> >> >> Yes, getting warning immediately, but once, and blaming host driver seems ok. > > We do know the fact of non-aligned transfer buffer from network, which has > been > for long time, so does it make sense to print warning and annoy people? It's only printed if host controller driver is not behaving correctly. I have changed the message to be printed for v2-patch, and it is now: dev_WARN_ONCE(hcd->self.controller, 1, "broken USB host controller driver; does not correctly handle DMA alignment for urb->transfer_buffer (offset: %d).\n", dma_offset); I sent the patch as RFC since I'm not sure.. maybe annoying warnings make people aware of issues that they don't yet know of and things get fixed? > >> URB buffers and let core/hcd.c to do the mapping on architectures that have minimum DMA alignment requirements. This leads to random memory corruptions and crashes when using USB device drivers that use unaligned URB buffers. >>> >>> Maybe you should check the dma mapping/unmapping implementation of >>> the arch, non-aligned buffer should have be covered by the API easily. >>> >>> Also USB Host controller should have supported non-aligned DMA buffer. >> >> From what I found, there was some discussion about these issues around 2010: >> >> http://lists.infradead.org/pipermail/linux-arm-kernel/2010-August/022983.html > > From the discussion, people think that HCD should handle the unaligned > buffer, > right? Yes, that's how I understood it. > >> >> To me, it seems that non-aligned buffers cannot be easily handled by all >> archs >> at dma mapping/unmapping phase and that HCD driver should do the alignment on > > If the memory which shares cache line with transfer buffer can't be > accessed during > DMA transfer(between URB submit and complete), dma mapping/unmapping > should have handled it. > > About the network transfer buffer case, I think it should be true, > otherwise there > should have lots of memory corruption reports about usb network drivers. > Fortunately, there are seldom such reports. > Another reason why rtl8192cu is so hard, is that it uses pre-allocated array for buffers of multiple URBs, and more than one transfer buffer can reside on same cache line. >> archs that set ARCH_DMA_MINALIGN. For example, ehci_tegra does copy unaligned >> transfer buffers to temporary aligned buffers before letting them to USB >> core. > > Yes, if host controller can't handle this, the HCD has to work around > the problem. Anyway, most of host controllers can deal with the it, > can't they? Can they? Maybe they can handle most cases of unaligned buffers, but not some corner cases, like transfer buffers on same cache line. > >> >>> Instead of fixing host drivers, users end up posting bug reports against those USB device drivers that use unaligned buffers for URB; such as with rtl8192cu (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). >>> >>> Not only rtl8192cu driver, all USB network device drivers have the problem. >>> Patch makes this issue more visible at core level, and hopefully gives hint for future hcd driver implementors about this problem. >>> >>> So please find the root cause first, and don't add the noise now. >> >> I think the root cause is that host driver is letting pass non-aligned >> buffers >> to core on archs that have ARCH_DMA_MINALIGN set. > > No, I don't think so, about the problem, the dma alignment requirement should > be from your host controller. > > As I said above, dma mapping/unmapping should be capable of dealing with > the unaligned buffer if no one touches memory which shares cacheline with > URB->transfer_buffer during URB transfer. How can you guarantee that when you allow unaligned URB buffers? You can have the buffer as part of some larger structure and send out async URB. Then while buffer is DMA mapped and send async to hw, you use other parts of that structure even if it shares cacheline with the buffer. You might issue multiple URBs with transfer buffers within same cacheline. I would expect that to be acceptable or URB documentation should say something against such. > > Looks you need to know why the memory corruption happens. Is it caused > by non-aligned arch mapping/unmapping? or by host controller hardware when > dealing with non-aligned transfer buffer? > >> The warni
Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
On Sat, Jun 15, 2013 at 6:19 PM, Jussi Kivilinna wrote: > On 15.06.2013 10:41, Ming Lei wrote: >> Cc: netdev >> >> On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna >> wrote: >>> Appearently some out-of-tree USB host drivers do not handle DMA alignment >>> for >> >> Looks these host drivers have to face the fact that the transfer buffer is >> often >> DMA non-aligned from network device drivers(in fact, the buffer is from >> network protocol stack), if you run usbnet, then you will get the added >> warning >> immediately. >> > > Yes, getting warning immediately, but once, and blaming host driver seems ok. We do know the fact of non-aligned transfer buffer from network, which has been for long time, so does it make sense to print warning and annoy people? > >>> URB buffers and let core/hcd.c to do the mapping on architectures that have >>> minimum DMA alignment requirements. This leads to random memory corruptions >>> and crashes when using USB device drivers that use unaligned URB buffers. >> >> Maybe you should check the dma mapping/unmapping implementation of >> the arch, non-aligned buffer should have be covered by the API easily. >> >> Also USB Host controller should have supported non-aligned DMA buffer. > > From what I found, there was some discussion about these issues around 2010: > http://lists.infradead.org/pipermail/linux-arm-kernel/2010-August/022983.html >From the discussion, people think that HCD should handle the unaligned buffer, right? > > To me, it seems that non-aligned buffers cannot be easily handled by all archs > at dma mapping/unmapping phase and that HCD driver should do the alignment on If the memory which shares cache line with transfer buffer can't be accessed during DMA transfer(between URB submit and complete), dma mapping/unmapping should have handled it. About the network transfer buffer case, I think it should be true, otherwise there should have lots of memory corruption reports about usb network drivers. Fortunately, there are seldom such reports. > archs that set ARCH_DMA_MINALIGN. For example, ehci_tegra does copy unaligned > transfer buffers to temporary aligned buffers before letting them to USB core. Yes, if host controller can't handle this, the HCD has to work around the problem. Anyway, most of host controllers can deal with the it, can't they? > >> >>> >>> Instead of fixing host drivers, users end up posting bug reports against >>> those USB device drivers that use unaligned buffers for URB; such as with >>> rtl8192cu >>> (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). >> >> Not only rtl8192cu driver, all USB network device drivers have the problem. >> >>> >>> Patch makes this issue more visible at core level, and hopefully gives hint >>> for future hcd driver implementors about this problem. >> >> So please find the root cause first, and don't add the noise now. > > I think the root cause is that host driver is letting pass non-aligned buffers > to core on archs that have ARCH_DMA_MINALIGN set. No, I don't think so, about the problem, the dma alignment requirement should be from your host controller. As I said above, dma mapping/unmapping should be capable of dealing with the unaligned buffer if no one touches memory which shares cacheline with URB->transfer_buffer during URB transfer. Looks you need to know why the memory corruption happens. Is it caused by non-aligned arch mapping/unmapping? or by host controller hardware when dealing with non-aligned transfer buffer? > The warning given just before such unaligned buffer is passed to > dma_map_single, > which requires ARCH_DMA_MINALIGN alignment. This seems reasonable to me. ARCH_DMA_MINALIGN means that kmalloc() should return aligned dma buffer. Again, you have to accept the fact in which transfer buffer from network stack is non-aligned. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
On 15.06.2013 10:41, Ming Lei wrote: > Cc: netdev > > On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna > wrote: >> Appearently some out-of-tree USB host drivers do not handle DMA alignment for > > Looks these host drivers have to face the fact that the transfer buffer is > often > DMA non-aligned from network device drivers(in fact, the buffer is from > network protocol stack), if you run usbnet, then you will get the added > warning > immediately. > Yes, getting warning immediately, but once, and blaming host driver seems ok. >> URB buffers and let core/hcd.c to do the mapping on architectures that have >> minimum DMA alignment requirements. This leads to random memory corruptions >> and crashes when using USB device drivers that use unaligned URB buffers. > > Maybe you should check the dma mapping/unmapping implementation of > the arch, non-aligned buffer should have be covered by the API easily. > > Also USB Host controller should have supported non-aligned DMA buffer. >From what I found, there was some discussion about these issues around 2010: http://lists.infradead.org/pipermail/linux-arm-kernel/2010-August/022983.html To me, it seems that non-aligned buffers cannot be easily handled by all archs at dma mapping/unmapping phase and that HCD driver should do the alignment on archs that set ARCH_DMA_MINALIGN. For example, ehci_tegra does copy unaligned transfer buffers to temporary aligned buffers before letting them to USB core. > >> >> Instead of fixing host drivers, users end up posting bug reports against >> those USB device drivers that use unaligned buffers for URB; such as with >> rtl8192cu >> (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). > > Not only rtl8192cu driver, all USB network device drivers have the problem. > >> >> Patch makes this issue more visible at core level, and hopefully gives hint >> for future hcd driver implementors about this problem. > > So please find the root cause first, and don't add the noise now. I think the root cause is that host driver is letting pass non-aligned buffers to core on archs that have ARCH_DMA_MINALIGN set. The warning given just before such unaligned buffer is passed to dma_map_single, which requires ARCH_DMA_MINALIGN alignment. This seems reasonable to me. -Jussi > > > Thanks, > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
On 14.06.2013 23:20, Alan Stern wrote: > On Fri, 14 Jun 2013, Jussi Kivilinna wrote: > >> Appearently some out-of-tree USB host drivers do not handle DMA alignment for >> URB buffers and let core/hcd.c to do the mapping on architectures that have >> minimum DMA alignment requirements. This leads to random memory corruptions >> and crashes when using USB device drivers that use unaligned URB buffers. >> >> Instead of fixing host drivers, users end up posting bug reports against >> those USB device drivers that use unaligned buffers for URB; such as with >> rtl8192cu >> (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). >> >> Patch makes this issue more visible at core level, and hopefully gives hint >> for future hcd driver implementors about this problem. >> >> Signed-off-by: Jussi Kivilinna > > It's probably okay to leave out the test for the setup buffer. That > thing is only 8 bytes long and is unlikely to be misaligned. The > transfer buffer is the one that matters. The rtl8192cu driver used to allocate the transfer buffer and the setup buffer with same kmalloc, so that setup and transfer buffers for same URB shared cache-line. This was causing pretty hard crashes with ARM/sunxi device I have. Before I realized that problem really was in the host controller driver, I made patch to rtl8192cu that changed code to use two separate kmallocs. Old code looked like: http://lxr.linux.no/linux+v3.7/drivers/net/wireless/rtlwifi/usb.c#L58 > > Also, the error message should include the name of the host controller > driver. How about using dev_WARN_ONCE(hcd->self.controller, ...)? Ah, thanks, didn't know about dev_WARN*. -Jussi > > Alan Stern > > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [RFC PATCH] usb: hcd: warn about URB buffers that are not DMA aligned and are about to be DMA mapped
Cc: netdev On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna wrote: > Appearently some out-of-tree USB host drivers do not handle DMA alignment for Looks these host drivers have to face the fact that the transfer buffer is often DMA non-aligned from network device drivers(in fact, the buffer is from network protocol stack), if you run usbnet, then you will get the added warning immediately. > URB buffers and let core/hcd.c to do the mapping on architectures that have > minimum DMA alignment requirements. This leads to random memory corruptions > and crashes when using USB device drivers that use unaligned URB buffers. Maybe you should check the dma mapping/unmapping implementation of the arch, non-aligned buffer should have be covered by the API easily. Also USB Host controller should have supported non-aligned DMA buffer. > > Instead of fixing host drivers, users end up posting bug reports against > those USB device drivers that use unaligned buffers for URB; such as with > rtl8192cu > (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). Not only rtl8192cu driver, all USB network device drivers have the problem. > > Patch makes this issue more visible at core level, and hopefully gives hint > for future hcd driver implementors about this problem. So please find the root cause first, and don't add the noise now. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
