tree 4dc158ae33a809d0e0f897cf5e4637a64beec225
parent 12bd7a16811bc250fee97f106a874720abd2346d
author Leo Yan <leo.yan@linaro.org> 1554686839 +0800
committer Will Deacon <will.deacon@arm.com> 1556286551 +0100

vfio-pci: Re-enable INTx mode when disable MSI/MSIX

Since PCI forbids enabling INTx, MSI or MSIX at the same time, it's by
default to disable INTx mode when enable MSI/MSIX mode; but this logic is
easily broken if the guest PCI driver detects the MSI/MSIX cannot work as
expected and tries to rollback to use INTx mode.  In this case, the INTx
mode has been disabled and has no chance to re-enable it, thus both INTx
mode and MSI/MSIX mode cannot work in vfio.

Below shows the detailed flow for introducing this issue:

  vfio_pci_configure_dev_irqs()
    `-> vfio_pci_enable_intx()

  vfio_pci_enable_msis()
    `-> vfio_pci_disable_intx()

  vfio_pci_disable_msis()   => Guest PCI driver disables MSI

To fix this issue, when disable MSI/MSIX we need to check if INTx mode
is available for this device or not; if the device can support INTx then
re-enable it so that the device can fallback to use it.

Since vfio_pci_disable_intx() / vfio_pci_enable_intx() pair functions
may be called for multiple times, this patch uses 'intx_fd == -1' to
denote the INTx is disabled, the pair functions can directly bail out
when detect INTx has been disabled and enabled respectively.

Suggested-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>