Re: [Xen-devel] swiotlb=force in Konrad's xen-pcifront-0.8.2 pvops domU kernel with PCI passthrough

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Nov 11, 2010 at 10:31:48AM -0800, Dante Cinco wrote:
> Konrad,
> 
> Without swiotlb=force, I don't see "PCI-DMA: Using software bounce
> buffering for IO" in /var/log/kern.log.
> 
> With iommu=soft and without swiotlb=force, I see the "software bounce
> buffering" in /var/log/kern.log and an NMI (see below) when I load the
> kernel module drivers. I made sure the NMI is reproducible and not a

What is the kernel module doing to cause this? DMA?
> one-time event.

So doing 64-bit DMA causes an NMI. Do you have the Hypervisor's IOMMU VT-d
enabled or disabled? (iommu=off,verbose) If you turn it off does this work?
> 
> /var/log/kern.log (iommu=soft):
> PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> Placing 64MB software IO TLB between ffff880005800000 - ffff880009800000
> software IO TLB at phys 0x5800000 - 0x9800000
> 
> (XEN)
> (XEN)
> (XEN) NMI - I/O ERROR
> (XEN) ----[ Xen-4.1-unstable  x86_64  debug=y  Not tainted ]----
> (XEN) CPU:    0
> (XEN) RIP:    e008:[<ffff82c4801701b2>] smp_send_event_check_mask+0x1/0x10
> (XEN) RFLAGS: 0000000000000012   CONTEXT: hypervisor
> (XEN) rax: 0000000000000080   rbx: ffff82c480287c48   rcx: 0000000000000000
> (XEN) rdx: 0000000000000080   rsi: 0000000000000080   rdi: ffff82c480287c48
> (XEN) rbp: ffff82c480287c78   rsp: ffff82c480287c38   r8:  0000000000000000
> (XEN) r9:  0000000000000037   r10: 0000ffff0000ffff   r11: 00ff00ff00ff00ff
> (XEN) r12: ffff82c48029f080   r13: 0000000000000001   r14: 0000000000000008
> (XEN) r15: ffff82c4802b0c20   cr0: 000000008005003b   cr4: 00000000000026f0
> (XEN) cr3: 00000001250a9000   cr2: 00007f6165ae9428
> (XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: e010   cs: e008
> (XEN) Xen stack trace from rsp=ffff82c480287c38:
> (XEN)    ffff82c480287c78 ffff82c48012001f 0000000000000100 0000000000000000
> (XEN)    ffff82c480287ca8 ffff83011dadd8b0 ffff83019fffa9d0 ffff82c4802c2300
> (XEN)    ffff82c480287cc8 ffff82c480117d0d ffff82c48029f080 0000000000000001
> (XEN)    0000000000000100 0000000000000000 0000000000000002 ffff8300df606000
> (XEN)    000000411de66867 ffff82c4802c2300 ffff82c480287d28 ffff82c48011f299
> (XEN)    0000000000000100 0000000000000086 ffff83019e3fa000 ffff83011dadd8b0
> (XEN)    ffff83019fffa9d0 ffff8300df606000 0000000000000000 0000000000000000
> (XEN)    000000000000007f ffff83019fe02200 ffff82c480287d38 ffff82c48011f6ea
> (XEN)    ffff82c480287d58 ffff82c48014e4c1 ffff83011dae2000 0000000000000066
> (XEN)    ffff82c480287d68 ffff82c48014e54d ffff82c480287d98 ffff82c480105d59
> (XEN)    ffff82c480287da8 ffff8301616a6990 ffff83011dae2000 0000000000000000
> (XEN)    ffff82c480287da8 ffff82c480105f81 ffff82c480287e28 ffff82c48015c043
> (XEN)    0000000000000043 0000000000000043 ffff83019fe02234 0000000000000000
> (XEN)    000000000000010c 0000000000000000 0000000000000000 0000000000000002
> (XEN)    ffff82c480287e10 ffff82c480287f18 ffff82c48024f6c0 ffff82c480287f18
> (XEN)    ffff82c4802c2300 0000000000000002 00007d3b7fd781a7 ffff82c480154ee6
> (XEN)    0000000000000002 ffff82c4802c2300 ffff82c480287f18 ffff82c48024f6c0
> (XEN)    ffff82c480287ee0 ffff82c480287f18 00ff00ff00ff00ff 0000ffff0000ffff
> (XEN)    0000000000000000 0000000000000000 ffff82c4802c23a0 0000000000000000
> (XEN)    0000000000000000 ffff82c4802c2e80 0000000000000000 0000007a00000000
> (XEN) Xen call trace:
> (XEN)    [<ffff82c4801701b2>] smp_send_event_check_mask+0x1/0x10
> (XEN)    [<ffff82c480117d0d>] csched_vcpu_wake+0x2e1/0x302
> (XEN)    [<ffff82c48011f299>] vcpu_wake+0x243/0x43e
> (XEN)    [<ffff82c48011f6ea>] vcpu_unblock+0x4a/0x4c
> (XEN)    [<ffff82c48014e4c1>] vcpu_kick+0x21/0x7f
> (XEN)    [<ffff82c48014e54d>] vcpu_mark_events_pending+0x2e/0x32
> (XEN)    [<ffff82c480105d59>] evtchn_set_pending+0xbf/0x190
> (XEN)    [<ffff82c480105f81>] send_guest_pirq+0x54/0x56
> (XEN)    [<ffff82c48015c043>] do_IRQ+0x3b2/0x59c
> (XEN)    [<ffff82c480154ee6>] common_interrupt+0x26/0x30
> (XEN)    [<ffff82c48014e3c3>] default_idle+0x82/0x87
> (XEN)    [<ffff82c480150664>] idle_loop+0x5a/0x68
> (XEN)
> (XEN)
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) FATAL TRAP: vector = 2 (nmi)
> (XEN) [error_code=0000] , IN INTERRUPT CONTEXT
> (XEN) ****************************************
> (XEN)
> (XEN) Reboot in five seconds...
> 
> Dante
> 
> 
> On Thu, Nov 11, 2010 at 8:04 AM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On Wed, Nov 10, 2010 at 05:16:14PM -0800, Dante Cinco wrote:
> >> We have Fibre Channel HBA devices that we PCI passthrough to our pvops
> >> domU kernel. Without swiotlb=force in the domU's kernel command line,
> >> both domU and dom0 lock up after loading the kernel module drivers for
> >> the HBA devices. With swiotlb=force, the domU and dom0 are stable
> >
> > Whoa. That is not good - what happens if you just pass in iommu=soft?
> > Does the PCI-DMA: Using.. show up if you don't pass in any of those 
> > parameters?
> > (I don't think it does, but just doing 'iommu=soft' should enable it).
> >
> >
> >> after loading the kernel module drivers but the I/O performance is at
> >> least an order of magnitude worse than what we were seeing with the
> >> HVM kernel. I see the following in /var/log/kern.log in the pvops
> >> domU:
> >>
> >> PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
> >> Placing 64MB software IO TLB between ffff880005800000 - ffff880009800000
> >> software IO TLB at phys 0x5800000 - 0x9800000
> >>
> >> Is swiotlb=force responsible for the I/O performance degradation? I
> >> don't understand what swiotlb=force does so I would appreciate an
> >> explanation or a pointer.
> >
> > So, you should only need to use 'iommu=soft'. It will enable the Linux 
> > kernel IOMMU
> > to translate the pseudo-PFNs to the real machine frame numbers (bus 
> > addresses).
> >
> > If your card is 64-bit, then that is all it would do. If however your card 
> > is 32-bit
> > and your are DMA-ing data from above the 32-bit limit, it would copy the 
> > user-space page
> > to memory below 4GB, DMA that, and when done, copy it back to the where the 
> > user-space
> > page is. This is called bounce-buffering and this is why you would use a 
> > mix of
> > pci_map_page, pci_sync_single_for_[cpu|device] calls around your driver.
> >
> > However, I think your cards are 64-bit, so you don't need this 
> > bounce-buffering. But
> > if you say 'swiotlb=force' it will force _all_ DMAs to go through the 
> > bounce-buffer.
> >
> > So, try just 'iommu=soft' and see what happens.
> >

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