On 2012-08-24 10:11, Michael S. Tsirkin wrote: > On Fri, Aug 24, 2012 at 07:59:06AM +0200, Jan Kiszka wrote: >> On 2012-08-24 01:13, Cam Macdonell wrote: >>> Hi Jan, >>> >>> I've bisected a bug in which MSI interrupts are not being delivered to >>> the following patch, where msix_reset was moved in tot he PCI core. >>> >>> commit cbd2d4342b3d42ab33baa99f5b7a23491b5692f2 >>> Author: Jan Kiszka <jan.kis...@siemens.com> >>> Date: Tue May 15 20:09:56 2012 -0300 >>> >>> msi: Invoke msi/msix_reset from PCI core >>> >>> There is no point in pushing this burden to the devices, they tend to >>> forget to call them (like intel-hda, ahci, xhci did). Instead, reset >>> functions are now called from pci_device_reset. They do nothing if >>> MSI/MSI-X is not in use. >>> >>> I've been debugging and it seems that when msix_notify() is triggered >>> the second test in the "if" fails >>> >>> /* Send an MSI-X message */ >>> void msix_notify(PCIDevice *dev, unsigned vector) >>> { >>> MSIMessage msg; >>> >>> if (vector >= dev->msix_entries_nr || !dev->msix_entry_used[vector]) >>> return; >>> >>> … >>> } >>> >>> here is some MSI-X debugging statements >>> >>> msix_init >>> IVSHMEM: msix initialized (1 vectors) >>> IVSHMEM: using vector 0 >>> IVSHMEM: ivshmem_reset >>> IVSHMEM: using vector 0 >>> msix_reset >>> msix_free_irq_entries 0x7fd52d1cea20 >>> >>> msix_free_irq_entries() sets dev->msix_entries_nr to 0, so I think it >>> may be the cause. >> >> I suppose you mean it sets the msix_entry_used array to 0. >> >>> >>> Shouldn't ivshmem's reset (which reenables the vectors) be triggered >>> by the msix_reset? >> >> Actually, the whole msix vector usage tracking is useless today, this >> just shows its downsides (in the absence of benefits). Megasas is >> affected by this problem as well, virtio not as it calls msix_vector_use >> during the configuration process the guest driver triggers. >> >> Two options: >> - I can send my removal patch for msix_vector_use/unuse that I was >> only planning for 1.3 so far, and we kill this pitfall earlier. >> - We re-add msix_vector_use calls to the affected device models for >> 1.2 and drop them later again for 1.3 when removing usage tracking. >> [The third option to keep the usage tracking is a non-option for me. ;)] >> >> Michael? > > Second option seems more prudent to me. Can you send a patch pls?
In fact, it's not as easy. ivshmem already tries to restore the usage flag but fails due to reset handler ordering. I do not see ATM where there is some "enable device" during re-initialization, at least for ivshmem. Haven't checked megasas yet. I tend to think removing is simpler and less risky. Please have a look at the patch I sent earlier. Jan
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