On Wed, Sep 28, 2016 at 07:45:32AM +1000, Benjamin Herrenschmidt wrote: >On Tue, 2016-09-27 at 14:20 -0500, Bjorn Helgaas wrote: >> On Mon, Sep 19, 2016 at 09:53:30AM +1000, Gavin Shan wrote: >> > In pci_update_resource(), the PCI device's memory decoding (0x2 in >> > PCI_COMMAND) is disabled when 64-bits memory BAR is updated if the >> > PCI device's memory space wasn't asked to be always on by @pdev-> >> > mmio_always_on. The PF's memory decoding might be disabled when >> > updating its IOV BARs in the following path. Actually, the PF's >> > memory decoding shouldn't be disabled in this scenario as the PF >> > has been started to provide services: >> >> The reason we disable memory decoding while updating a 64-bit BAR is >> because we can't do the update atomically, and a half-updated BAR might >> conflict with other devices. >> >> You need to explain what is special about these SR-IOV BARs that makes it >> safe to update them non-atomically while decoding is enabled. > >The IOV BAR won't decode until SR-IOV is enabled right ? Gavin, I don't >think we update it "live", so it should be safe... > Yeah, it's safe to update it with memory decoding on. As the function call flow I listed in the changelog (as below), nobody should access the IOV BAR when pci_update_resource() is called. However, the PF's memory BARs might be accessed that time and it's not safe to disable PF's memory decoding. sriov_numvfs_store pdev->driver->sriov_configure mlx5_core_sriov_configure pci_enable_sriov sriov_enable pcibios_sriov_enable pnv_pci_sriov_enable pnv_pci_vf_resource_shift pci_update_resource Thanks, Gavin -- 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
