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Re: [PATCH-for-6.2] docs: add a word of caution on x-native-hotplug prop


From: Michael S. Tsirkin
Subject: Re: [PATCH-for-6.2] docs: add a word of caution on x-native-hotplug property for pcie-root-ports
Date: Thu, 25 Nov 2021 15:49:50 -0500

On Thu, Nov 25, 2021 at 05:36:29PM +0530, Ani Sinha wrote:
> x-native-hotplug property, when used in order to disable HPC bit on the PCIE
> root ports, can lead to unexpected results from the guest operating system.
> Users are strongly advised not to touch this property in order to manipulte 
> the
> HPC bit. Add a word of caution in the pcie.txt doc file to document this.
> 
> Signed-off-by: Ani Sinha <ani@anisinha.ca>

Do we want to generally document this for all "x-" options?

> ---
>  docs/pcie.txt | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/pcie.txt b/docs/pcie.txt
> index 89e3502075..e1f99f725f 100644
> --- a/docs/pcie.txt
> +++ b/docs/pcie.txt
> @@ -262,11 +262,26 @@ PCI Express Root Ports (and PCI Express Downstream 
> Ports).
>          Port, which may come handy for hot-plugging another device.
>  
>  
> -5.3 Hot-plug example:
> +5.2 Hot-plug example:
>  Using HMP: (add -monitor stdio to QEMU command line)
>    device_add <dev>,id=<id>,bus=<PCI Express Root Port Id/PCI Express 
> Downstream Port Id/PCI-PCI Bridge Id/>
>  
>  
> +5.3 A word of caution using hotplug on PCI Express Root Ports:
> +Starting Qemu version 6.2, PCI Express Root ports have a property
> +"x-native-hotplug" ("native-hotplug" for Qemu version 6.1), that can be used 
> to
> +enable or disable hotplug on that port. For example:
> +
> +-device pcie-root-port,x-native-hotplug=off,... etc.
> +
> +The "x-" prefix indicates that this property is highly experimental and can
> +lead to unexpected results from the guest operating system if users try to 
> use
> +it to alter the native hotplug on the port. It also means that the property
> +name and its behavior is liable to change in the future and is not expected 
> to
> +be stable across Qemu versions. Therefore, end users are advised not to 
> change
> +the value of this option from its default set value or use it in the Qemu
> +command line.
> +
>  6. Device assignment
>  ====================
>  Host devices are mostly PCI Express and should be plugged only into
> -- 
> 2.25.1




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