Re: [PATCH v2 2/2] PCI: hv: Propagate coherence from VMbus device to PCI device

Boqun Feng
2022-03-24T01:10:08Z

On Wed, Mar 23, 2022 at 01:31:12PM -0700, Michael Kelley wrote:
> PCI pass-thru devices in a Hyper-V VM are represented as a VMBus
> device and as a PCI device. The coherence of the VMbus device is
> set based on the VMbus node in ACPI, but the PCI device has no
> ACPI node and defaults to not hardware coherent. This results
> in extra software coherence management overhead on ARM64 when
> devices are hardware coherent.
>
> Fix this by setting up the PCI host bus so that normal
> PCI mechanisms will propagate the coherence of the VMbus
> device to the PCI device. There's no effect on x86/x64 where
> devices are always hardware coherent.
>
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>

Acked-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> ---
> drivers/pci/controller/pci-hyperv.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index ae0bc2f..88b3b56 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -3404,6 +3404,15 @@ static int hv_pci_probe(struct hv_device *hdev,
> hbus->bridge->domain_nr = dom;
> #ifdef CONFIG_X86
> hbus->sysdata.domain = dom;
> +#elif defined(CONFIG_ARM64)
> + /*
> + * Set the PCI bus parent to be the corresponding VMbus
> + * device. Then the VMbus device will be assigned as the
> + * ACPI companion in pcibios_root_bridge_prepare() and
> + * pci_dma_configure() will propagate device coherence
> + * information to devices created on the bus.
> + */
> + hbus->sysdata.parent = hdev->device.parent;
> #endif
>
> hbus->hdev = hdev;
> --
> 1.8.3.1
>
>