Re: [PATCH v8 11/12] PCI: liveupdate: Do not disable bus mastering on preserved devices during kexec

[Samiullah Khawaja]

On Tue, Jul 28, 2026 at 10:10:05PM +0000, David Matlack wrote:
> Do not disable bus mastering on outgoing preserved devices during
> pci_device_shutdown() for kexec.
>
> Preserved devices must be allowed to perform memory transactions during
> a Live Update to ensure continuous operation.  Clearing the bus
> mastering bit would prevent these devices from issuing any memory
> requests while the new kernel boots.
>
> Because bridges upstream of preserved endpoint devices are also
> automatically preserved, this change also avoids clearing bus mastering
> on them. This is critical because clearing bus mastering on an upstream
> bridge prevents the bridge from forwarding memory requests upstream (i.e.
> it would prevent the endpoint device from accessing system RAM and doing
> peer-to-peer transactions with devices not downstream of the bridge).
>
> Reviewed-by: Pranjal Shrivastava <praan@xxxxxxxxxx>
> Reviewed-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> ---
> drivers/pci/liveupdate.c | 11 +++++++++++
> drivers/pci/liveupdate.h |  6 ++++++
> drivers/pci/pci-driver.c |  7 +++++--
> 3 files changed, 22 insertions(+), 2 deletions(-)

Reviewed-by: Samiullah Khawaja <skhawaja@xxxxxxxxxx>