Re: [PATCH v4 6/7] xen/arm: introduce new xen,enhanced property value

From: Stefano Stabellini <sstabellini@kernel.org>
To: Rahul Singh <rahul.singh@arm.com>
Cc: xen-devel@lists.xenproject.org,
	 Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>,
	 Bertrand Marquis <bertrand.marquis@arm.com>,
	 Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH v4 6/7] xen/arm: introduce new xen,enhanced property value
Date: Tue, 6 Sep 2022 15:12:50 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.22.394.2209061507481.157835@ubuntu-linux-20-04-desktop> (raw)
In-Reply-To: <667059a3bc6ed9a8b993f64f2b1176a2a131f41e.1662462034.git.rahul.singh@arm.com>

On Tue, 6 Sep 2022, Rahul Singh wrote:
> Introduce a new "xen,enhanced" dom0less property value "no-xenstore" to
> disable xenstore interface for dom0less guests.
> 
> Signed-off-by: Rahul Singh <rahul.singh@arm.com>
> ---
> Changes in v4:
>  - Implement defines for dom0less features
> Changes in v3:
>  - new patch in this version
> ---
>  docs/misc/arm/device-tree/booting.txt |  4 ++++
>  xen/arch/arm/domain_build.c           | 10 ++++++----
>  xen/arch/arm/include/asm/kernel.h     | 23 +++++++++++++++++++++--
>  3 files changed, 31 insertions(+), 6 deletions(-)
> 
> diff --git a/docs/misc/arm/device-tree/booting.txt b/docs/misc/arm/device-tree/booting.txt
> index 98253414b8..1b0dca1454 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -204,6 +204,10 @@ with the following properties:
>      - "disabled"
>      Xen PV interfaces are disabled.
>  
> +    - no-xenstore
> +    Xen PV interfaces, including grant-table will be enabled but xenstore
> +    will be disabled for the VM.

Please use "" for consistency:

    - "no-xenstore"

>      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.
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 707e247f6a..0b164ef595 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -2891,7 +2891,7 @@ static int __init prepare_dtb_domU(struct domain *d, struct kernel_info *kinfo)
>              goto err;
>      }
>  
> -    if ( kinfo->dom0less_enhanced )
> +    if ( kinfo->dom0less_feature & DOM0LESS_ENHANCED_NO_XS )
>      {
>          ret = make_hypervisor_node(d, kinfo, addrcells, sizecells);
>          if ( ret )
> @@ -3209,10 +3209,12 @@ static int __init construct_domU(struct domain *d,
>           (rc == 0 && !strcmp(dom0less_enhanced, "enabled")) )
>      {
>          if ( hardware_domain )
> -            kinfo.dom0less_enhanced = true;
> +            kinfo.dom0less_feature = DOM0LESS_ENHANCED;
>          else
> -            panic("Tried to use xen,enhanced without dom0\n");
> +            panic("At the moment, Xenstore support requires dom0 to be present\n");
>      }
> +    else if ( rc == 0 && !strcmp(dom0less_enhanced, "no-xenstore") )
> +        kinfo.dom0less_feature = DOM0LESS_ENHANCED_NO_XS;
>  
>      if ( vcpu_create(d, 0) == NULL )
>          return -ENOMEM;
> @@ -3252,7 +3254,7 @@ static int __init construct_domU(struct domain *d,
>      if ( rc < 0 )
>          return rc;
>  
> -    if ( kinfo.dom0less_enhanced )
> +    if ( kinfo.dom0less_feature & DOM0LESS_XENSTORE )
>      {
>          ASSERT(hardware_domain);
>          rc = alloc_xenstore_evtchn(d);
> diff --git a/xen/arch/arm/include/asm/kernel.h b/xen/arch/arm/include/asm/kernel.h
> index c4dc039b54..ad240494ea 100644
> --- a/xen/arch/arm/include/asm/kernel.h
> +++ b/xen/arch/arm/include/asm/kernel.h
> @@ -9,6 +9,25 @@
>  #include <xen/device_tree.h>
>  #include <asm/setup.h>
>  
> +/*
> + * List of possible features for dom0less domUs
> + *
> + * DOM0LESS_ENHANCED_NO_XS: Notify the OS it is running on top of Xen. All the
> + *                          default features (excluding Xenstore) will be
> + *                          available. Note that an OS *must* not rely on the
> + *                          availability of Xen features if this is not set.
> + * DOM0LESS_XENSTORE:       Xenstore will be enabled for the VM. This feature
> + *                          can't be enabled without the
> + *                          DOM0LESS_ENHANCED_NO_XS.
> + * DOM0LESS_ENHANCED:       Notify the OS it is running on top of Xen. All the
> + *                          default features (including Xenstore) will be
> + *                          available. Note that an OS *must* not rely on the
> + *                          availability of Xen features if this is not set.
> + */
> +#define DOM0LESS_ENHANCED_NO_XS  BIT(0, U)
> +#define DOM0LESS_XENSTORE        BIT(1, U)
> +#define DOM0LESS_ENHANCED        (DOM0LESS_ENHANCED_NO_XS | DOM0LESS_XENSTORE)
> +
>  struct kernel_info {
>  #ifdef CONFIG_ARM_64
>      enum domain_type type;
> @@ -36,8 +55,8 @@ struct kernel_info {
>      /* Enable pl011 emulation */
>      bool vpl011;
>  
> -    /* Enable PV drivers */
> -    bool dom0less_enhanced;
> +    /* Enable/Disable PV drivers interface,grant table, evtchn or xenstore */

missing a whitespace

> +    uint32_t dom0less_feature;

Given that we only really need 2 bits today, and given that uint8_t and
uint16_t are free but uint32_t increases the size of the struct, could
we just use uint16_t dom0less_feature ?

Everything else looks good, these are just minor things.

>      /* GIC phandle */
>      uint32_t phandle_gic;
> -- 
> 2.25.1
> 