On Thu, May 14, 2026 at 05:24:46PM +0200, Pratyush Yadav wrote: > On Wed, May 13 2026, Samiullah Khawaja wrote: > > > On Tue, May 12, 2026 at 02:29:19PM -0700, Vipin Sharma wrote: > >>On Tue, May 12, 2026 at 01:59:51PM -0700, David Matlack wrote: > >>> On Mon, May 11, 2026 at 4:48 PM Vipin Sharma <[email protected]> wrote: > >>> > >>> > diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig > >>> > index c12d614fc6c4..019de053f116 100644 > >>> > --- a/drivers/vfio/pci/Kconfig > >>> > +++ b/drivers/vfio/pci/Kconfig > >>> > @@ -45,13 +45,15 @@ config VFIO_PCI_IGD > >>> > > >>> > config VFIO_PCI_LIVEUPDATE > >>> > bool "VFIO PCI support for Live Update (EXPERIMENTAL)" > >>> > - depends on PCI_LIVEUPDATE > >>> > + depends on PCI_LIVEUPDATE && VFIO_DEVICE_CDEV > >>> > help > >>> > Support for preserving devices bound to vfio-pci across a Live > >>> > Update. This option should only be enabled by developers > >>> > working on > >>> > implementing this support. Once enough support has landed in > >>> > the > >>> > kernel, this option will no longer be marked EXPERIMENTAL. > >>> > > >>> > + Enabling this will disable support for VFIO PCI DMA buffer. > >>> > + > >>> > If you don't know what to do here, say N. > >>> > > >>> > endif > >>> > @@ -68,7 +70,7 @@ config VFIO_PCI_ZDEV_KVM > >>> > To enable s390x KVM vfio-pci extensions, say Y. > >>> > > >>> > config VFIO_PCI_DMABUF > >>> > - def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER > >>> > + def_bool y if VFIO_PCI_CORE && PCI_P2PDMA && DMA_SHARED_BUFFER > >>> > && !VFIO_PCI_LIVEUPDATE > >>> > >>> Why does enabling VFIO_PCI_LIVEUPDATE require disabling > >>> VFIO_PCI_DMABUF? I saw the cover letter says "to keep things simple", > >>> but what specific problem does this solve or simplify? > >> > >>I should have provided more details there. > >> > >>When device is getting reset in vfio_pci_liveupdate_freeze(), we are > >>zapping userspace mapped bars, we also need to use > >>vfio_pci_dma_buf_move() to revoke dma buffer access or > >>vfio_pci_dma_buf_cleanup() combination. Cleanup takes the memory lock > >>which freeze already takes, and there are some refcounts which are > >>managed in both of these APIs. This was causing complexities with code > >>flow based on result of pci_load_saved_state(). All this was adding more > >>refactoring than I wanted in the series. > > > > Maybe we can return -EOPNOTSUPP if any dmabufs for this vfio cdev are > > exported during preserve?
Currently, no APIs are present to fetch if dmabufs are exported or not. I will add one patch to this series to return EOPNOTSUPP and remove condition from the config. > > Whichever way you go with, a TODO/comment would be nice to have so > someone (including future you) looking at this code knows why this > restriction exists. > I will add comment in the next version.
