Re: [PATCH v3 1/5] xen: introduce xen,enhanced dom0less property

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 28/01/2022 21:33, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
>
> Introduce a new "xen,enhanced" dom0less property to enable/disable PV
> driver interfaces for dom0less guests. Currently only "enabled" and
> "disabled" are supported property values (and empty). Leave the option
> open to implement further possible values in the future (e.g.
> "xenstore" to enable only xenstore.)
>
> The configurable option is for domUs only. For dom0 we always set the
> corresponding property in the Xen code to true (PV interfaces enabled.)
>
> This patch only parses the property. Next patches will make use of it.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
> CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> ---
> Changes in v3:
> - improve commit message
>
> Changes in v2:
> - rename kinfo.enhanced to kinfo.dom0less_enhanced
> - set kinfo.dom0less_enhanced to true for dom0
> - handle -ENODATA in addition to -EILSEQ
> ---
>   docs/misc/arm/device-tree/booting.txt | 18 ++++++++++++++++++
>   xen/arch/arm/domain_build.c           |  8 ++++++++
>   xen/arch/arm/include/asm/kernel.h     |  3 +++
>   3 files changed, 29 insertions(+)
>
> diff --git a/docs/misc/arm/device-tree/booting.txt 
> b/docs/misc/arm/device-tree/booting.txt
> index 71895663a4..38c29fb3d8 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -169,6 +169,24 @@ with the following properties:
>       Please note that the SPI used for the virtual pl011 could clash with the
>       physical SPI of a physical device assigned to the guest.
>   
> +- xen,enhanced
NIT: I find a bit strange this is added in the middle of the property. 
Can you either sort the property alphabtically or move this one to the end?
> +
> +    A string property. Possible property values are:
> +
> +    - "enabled" (or missing property value)
> +    Xen PV interfaces, including grant-table and xenstore, will be
> +    enabled for the VM.
> +
> +    - "disabled"
> +    Xen PV interfaces are disabled.
> +
> +    If the xen,enhanced property is present with no value, it defaults
> +    to "enabled". If the xen,enhanced property is not present, PV
> +    interfaces are disabled.
> +
> +    In the future other possible property values might be added to
> +    enable only selected interfaces.
> +
>   - nr_spis
>   
>       Optional. A 32-bit integer specifying the number of SPIs (Shared
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 6931c022a2..9144d6c0b6 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -2963,6 +2963,7 @@ static int __init construct_domU(struct domain *d,
>                                    const struct dt_device_node *node)
>   {
>       struct kernel_info kinfo = {};
> +    const char *dom0less_enhanced;
>       int rc;
>       u64 mem;
>   
> @@ -2978,6 +2979,12 @@ static int __init construct_domU(struct domain *d,
>   
>       kinfo.vpl011 = dt_property_read_bool(node, "vpl011");
>   
> +    rc = dt_property_read_string(node, "xen,enhanced", &dom0less_enhanced);
> +    if ( rc == -EILSEQ ||
I think the use an -EILSEQ wants an explanation. In a previous version, 
you wrote that the value would be returned when:
fdt set /chosen/domU0 xen,enhanced

But it is not clear why. Can you print pp->value, pp->length, 
strnlen(..) when this happens?

> +         rc == -ENODATA ||
> +         (rc == 0 && !strcmp(dom0less_enhanced, "enabled")) )
> +        kinfo.dom0less_enhanced = true;
> +
>       if ( vcpu_create(d, 0) == NULL )
>           return -ENOMEM;
>   
> @@ -3095,6 +3102,7 @@ static int __init construct_dom0(struct domain *d)
>   
>       kinfo.unassigned_mem = dom0_mem;
>       kinfo.d = d;
> +    kinfo.dom0less_enhanced = true;
This is a bit odd. The name suggests that this is a dom0less specific 
option. But then you are setting it to dom0.
Given that this variable is about enable PV drivers, I think this should 
be false for dom0.
>   
>       rc = kernel_probe(&kinfo, NULL);
>       if ( rc < 0 )
> diff --git a/xen/arch/arm/include/asm/kernel.h 
> b/xen/arch/arm/include/asm/kernel.h
> index 874aa108a7..c4dc039b54 100644
> --- a/xen/arch/arm/include/asm/kernel.h
> +++ b/xen/arch/arm/include/asm/kernel.h
> @@ -36,6 +36,9 @@ struct kernel_info {
>       /* Enable pl011 emulation */
>       bool vpl011;
>   
> +    /* Enable PV drivers */
> +    bool dom0less_enhanced;
> +
>       /* GIC phandle */
>       uint32_t phandle_gic;
>   
Cheers,

--
Julien Grall