On Sun, 4 Dec 2016 20:16:42 +0800 Cao jin <caoj.f...@cn.fujitsu.com> wrote:
> On 12/01/2016 10:55 PM, Alex Williamson wrote: > > On Thu, 1 Dec 2016 21:40:00 +0800 > > >>> If an AER fault occurs and the user doesn't do a reset, what > >>> happens when that device is released and a host driver tries to make > >>> use of it? The user makes no commitment to do a reset and there are > >>> only limited configurations where we even allow the user to perform a > >>> reset. > >>> > >> > >> Limited? Do you mean the things __pci_dev_reset() can do? > > > > I mean that there are significant device and guest configuration > > restrictions in order to support AER. For instance, all the functions > > of the slot need to appear in a PCI-e topology in the guest with all > > the functions in the right place such that a guest bus reset translates > > into a host bus reset. The physical functions cannot be split between > > guests even if IOMMU isolation would otherwise allow it. The user > > needs to explicitly enable AER support for the devices. A VM need to > > be specifically configured for AER support in order to set any sort of > > expectations of a guest directed bus reset, let alone a guarantee that > > it will happen. So all the existing VMs, where functions are split > > between guests, or the topology isn't exactly right, or AER isn't > > enabled see a regression from the above change as the device is no > > longer reset. > > > > I am not clear why set these restrictions in the current design. I take > a glance at older versions of qemu's patchset, their thoughts is: > translate a guest bus reset into a host bus reset(Which is > unreasonable[*] to me). And I guess, that's the *cause* of these > restrictions? Is there any other stories behind these restrictions? > > [*] In physical world, set bridge's secondary bus reset would send > hot-reset TLP to all functions below, trigger every device's reset > separately. Emulated device should behave the same, means just using > each device's DeviceClass->reset method. Are you trying to say that an FLR is equivalent to a link reset? Please go read the previous discussions, especially if you're sending patches you don't believe in. Thanks, Alex
