[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4] VT-d: fix VF of RC integrated PF matched to wrong VT-d unit
On Wed, Jul 05, 2017 at 09:29:29AM +0100, Roger Pau Monné wrote: >On Wed, Jul 05, 2017 at 02:19:17AM -0600, Jan Beulich wrote: >> >>> On 05.07.17 at 09:56, <chao.gao@xxxxxxxxx> wrote: >> > How about changing the second paragraph to: >> > >> > If a PF is an extended function, the BDF of a traditional function >> > within the same device should be used to search VT-d unit. Otherwise, >> > the real BDF of PF should be used. According PCI-e spec, an extended >> > function is a function within an ARI device and Function Number > 7. >> > But the original code only checks the latter requirement, without >> > checking the former requirement. It incurs that a function whose Function >> > Number > 7 but which isn't within an ARI device (such as RC integrated >> > function with Function Number > 7) is wrongly classified to an extended >> > function and then we wrongly use 0 as 'devfn' to search VT-d unit for this >> > case. >> >> There's one part here which I continue to not understand: The >> function number being just 3 bits, how can it possibly be larger >> than 7? > >It's a special case on the PCIe spec, quoting it: > >"Note: for Requests targeting Extended Functions in an ARI Device, >A[19:12] represents the (8-bit) Function Number, which replaces the >(5-bit) Device Number and (3-bit) Function Number fields above." > >It's in the PCIe 3.1a spec, page 657. The function number is expanded >from 7 to 255. > >What I fail to see is how this device is registered with Xen, is the >devfn field used to store the function number only? The devfn is passed down by dom0. Judging from how is_extfn is set in xen_add_device() in linux kernel, I think linux kernel reuses the Device Fields as the higher 5 bits of an extended function's Function Number. Thanks Chao _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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