On 06/02/2025 02:08, Stefano Stabellini wrote:
> The new xenstore page allocation scheme might break older unpatches
> Linux kernels that do not check for the Xenstore connection status
> before proceeding with Xenstore initialization.
>
> Introduce a dom0less configuration option to retain the older behavior,
> which is not compatible with 1:1 mapped guests, but it will work with
The issue is for static domains in general - not only for 1:1 guests.
Static domains without direct map will simply fail on acquire_reserved_page().
> older legacy kernel versions.
>
> Signed-off-by: Stefano Stabellini <stefano.stabell...@amd.com>
> ---
> docs/misc/arm/device-tree/booting.txt | 5 +++++
> xen/arch/arm/dom0less-build.c | 13 ++++++++++++-
> xen/arch/arm/include/asm/kernel.h | 14 +++++++++++---
> 3 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/docs/misc/arm/device-tree/booting.txt
> b/docs/misc/arm/device-tree/booting.txt
> index ff70d44462..8fa3da95be 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -222,6 +222,11 @@ with the following properties:
> Xen PV interfaces, including grant-table and xenstore, will be
> enabled for the VM.
>
> + - "legacy"
> + Same as above, but the way the xenstore page is allocated is not
> + compatible with 1:1 mapped guests. On the other hand, it works with
Same remark about 1:1
> + older Linux kernels.
> +
> - "disabled"
> Xen PV interfaces are disabled.
>
> diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
> index 046439eb87..9afdbca8b8 100644
> --- a/xen/arch/arm/dom0less-build.c
> +++ b/xen/arch/arm/dom0less-build.c
> @@ -799,6 +799,13 @@ static int __init construct_domU(struct domain *d,
> else
> panic("At the moment, Xenstore support requires dom0 to be
> present\n");
> }
> + else if ( rc == 0 && !strcmp(dom0less_enhanced, "legacy") )
> + {
> + if ( hardware_domain )
> + kinfo.dom0less_feature = DOM0LESS_ENHANCED_LEGACY;
> + else
> + 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;
>
> @@ -848,13 +855,17 @@ static int __init construct_domU(struct domain *d,
> if ( rc < 0 )
> return rc;
>
> - if ( kinfo.dom0less_feature & DOM0LESS_XENSTORE )
> + if ( kinfo.dom0less_feature & (DOM0LESS_XENSTORE|DOM0LESS_XS_LEGACY) )
Spaces around | operator.
> {
> ASSERT(hardware_domain);
> rc = alloc_xenstore_evtchn(d);
> if ( rc < 0 )
> return rc;
> + d->arch.hvm.params[HVM_PARAM_STORE_PFN] = ~0ULL;
> + }
>
> + if ( kinfo.dom0less_feature & DOM0LESS_XENSTORE )
> + {
Can I talk you into moving all of these into separate function e.g.
alloc_xenstore_params(struct kernel_info *kinfo)?
It would simplify construct_domU() in which we tend to just call functions
responsible for a given functionality.
> rc = alloc_xenstore_page(d);
> if ( rc < 0 )
> return rc;
> diff --git a/xen/arch/arm/include/asm/kernel.h
> b/xen/arch/arm/include/asm/kernel.h
> index de3f945ae5..4c2ae0b32b 100644
> --- a/xen/arch/arm/include/asm/kernel.h
> +++ b/xen/arch/arm/include/asm/kernel.h
> @@ -17,16 +17,24 @@
> * 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_XENSTORE: Xenstore will be enabled for the VM. The
> + * xenstore page allocation is done by Xen at
> + * domain creation. This feature can't be
> + * enabled without the DOM0LESS_ENHANCED_NO_XS.
> + * DOM0LESS_XS_LEGACY Xenstore will be enabled for the VM, the
> + * xenstore page allocation will happen in
> + * init-dom0less. 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.
> + * DOM0LESS_ENHANCED_LEGACY:Same as before, but using DOM0LESS_XS_LEGACY.
NIT: I would just >> all text by one to have a space after :
> */
> #define DOM0LESS_ENHANCED_NO_XS BIT(0, U)
> #define DOM0LESS_XENSTORE BIT(1, U)
> +#define DOM0LESS_XS_LEGACY BIT(2, U)
> +#define DOM0LESS_ENHANCED_LEGACY (DOM0LESS_ENHANCED_NO_XS |
> DOM0LESS_XS_LEGACY)
> #define DOM0LESS_ENHANCED (DOM0LESS_ENHANCED_NO_XS |
> DOM0LESS_XENSTORE)
>
> struct kernel_info {
Otherwise, patch is ok.
~Michal
