Re: [Qemu-devel] [PATCH 2/2] pcie_root_port: Disable ACS on older machines

[Igor Mammedov]

On Tue, 30 Jul 2019 10:37:19 +0100
"Dr. David Alan Gilbert (git)" <address@hidden> wrote:

> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> ACS got added in 4.0 unconditionally,  that broke older<->4.0 migration
> where there was a PCIe root port.
> Fix this by turning it off for 3.1 and older machines; note this
> fixes compatibility for older QEMUs but breaks compatibility with 4.0
> for older machine types.
> 
>     machine type    source qemu   dest qemu
>        3.1             3.1           4.0        broken
>        3.1             3.1           4.1rc2     broken
>        3.1             3.1           4.1+this   OK ++
>        3.1             4.0           4.1rc2     OK
>        3.1             4.0           4.1+this   broken --
>        4.0             4.0           4.1rc2     OK
>        4.0             4.0           4.1+this   OK
> 
> So we gain and lose; the consensus seems to be treat this as a
> fix for older machine types.
> 
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>

Reviewed-by: Igor Mammedov <address@hidden>

> ---
>  hw/core/machine.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index c58a8e594e..26a5f30e6d 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -52,6 +52,7 @@ GlobalProperty hw_compat_3_1[] = {
>      { "virtio-blk-device", "discard", "false" },
>      { "virtio-blk-device", "write-zeroes", "false" },
>      { "virtio-balloon-device", "qemu-4-0-config-size", "false" },
> +    { "pcie-root-port-base", "disable-acs", "true" }, /* Added in 4.1 */
>  };
>  const size_t hw_compat_3_1_len = G_N_ELEMENTS(hw_compat_3_1);
>