Re: [PATCH v4 05/10] xen/domain: Add DOMCTL handler for claiming memory with NUMA awareness

["Teddy Astie" <teddy.astie@xxxxxxxxxx>]

Le 26/02/2026 à 15:54, Bernhard Kaindl a écrit :
> Add a DOMCTL handler for claiming memory with NUMA awareness. It
> rejects claims when LLC coloring (does not support claims) is enabled
> and translates the public constant to the internal NUMA_NO_NODE.
>
> The request is forwarded to domain_set_outstanding_pages() for the
> actual claim processing. The handler uses the same XSM hook as the
> legacy XENMEM_claim_pages hypercall.
>
> While the underlying infrastructure currently supports only a single
> claim, the public hypercall interface is designed to be extensible for
> multiple claims in the future without breaking the API.
>

I'm not sure about the idea of introducing a new hypercall for this
operation. Though I may be missing some context about the reasons of
introducing a new hypercall.

XENMEM_claim_pages doesn't have actual support for NUMA, but the
hypercall interface seems to define it (e.g you can pass
XENMEMF_exact_node(n) to mem_flags). Would it be preferable instead to
make XENMEM_claim_pages aware of NUMA-related XENMEMF flags ?

> Signed-off-by: Bernhard Kaindl <bernhard.kaindl@xxxxxxxxxx>
> ---
>   xen/common/domain.c         | 29 ++++++++++++++++++++++++++++
>   xen/common/domctl.c         |  9 +++++++++
>   xen/include/public/domctl.h | 38 +++++++++++++++++++++++++++++++++++++
>   xen/include/xen/domain.h    |  2 ++
>   4 files changed, 78 insertions(+)
>
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index e7861259a2b3..ac1b091f5574 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -268,6 +268,35 @@ int get_domain_state(struct xen_domctl_get_domain_state 
> *info, struct domain *d,
>       return rc;
>   }
>
> +/* Claim memory for a domain or reset the claim */
> +int claim_memory(struct domain *d, const struct xen_domctl_claim_memory 
> *uinfo)
> +{
> +    memory_claim_t claim;
> +
> +    /* alloc_color_heap_page() does not handle claims, so reject LLC 
> coloring */
> +    if ( llc_coloring_enabled )
> +        return -EOPNOTSUPP;
> +    /*
> +     * We only support single claims at the moment, and if the domain is
> +     * dying (d->is_dying is set), its claims have already been released
> +     */
> +    if ( uinfo->pad || uinfo->nr_claims != 1 || d->is_dying )
> +        return -EINVAL;
> +
> +    if ( copy_from_guest(&claim, uinfo->claims, 1) )
> +        return -EFAULT;
> +
> +    if ( claim.pad )
> +        return -EINVAL;
> +
> +    /* Convert the API tag for a host-wide claim to the NUMA_NO_NODE 
> constant */
> +    if ( claim.node == XEN_DOMCTL_CLAIM_MEMORY_NO_NODE )
> +        claim.node = NUMA_NO_NODE;
> +
> +    /* NB. domain_set_outstanding_pages() has the checks to validate its 
> args */
> +    return domain_set_outstanding_pages(d, claim.pages, claim.node);
> +}
> +
>   static void __domain_finalise_shutdown(struct domain *d)
>   {
>       struct vcpu *v;
> diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> index 29a7726d32d0..9e858f631aaf 100644
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -868,6 +868,15 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
> u_domctl)
>           ret = get_domain_state(&op->u.get_domain_state, d, &op->domain);
>           break;
>
> +    case XEN_DOMCTL_claim_memory:
> +        /* Use the same XSM hook as XENMEM_claim_pages */
> +        ret = xsm_claim_pages(XSM_PRIV, d);
> +        if ( ret )
> +            break;
> +
> +        ret = claim_memory(d, &op->u.claim_memory);
> +        break;
> +
>       default:
>           ret = arch_do_domctl(op, d, u_domctl);
>           break;
> diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
> index 8f6708c0a7cd..610806c8b6e0 100644
> --- a/xen/include/public/domctl.h
> +++ b/xen/include/public/domctl.h
> @@ -1276,6 +1276,42 @@ struct xen_domctl_get_domain_state {
>       uint64_t unique_id;      /* Unique domain identifier. */
>   };
>
> +/*
> + * XEN_DOMCTL_claim_memory
> + *
> + * Claim memory for a guest domain. The claimed memory is converted into 
> actual
> + * memory pages by allocating it. Except for the option to pass claims for
> + * multiple NUMA nodes, the semantics are based on host-wide claims as
> + * provided by XENMEM_claim_pages, and are identical for host-wide claims.
> + *
> + * The initial implementation supports a claim for the host or a NUMA node, 
> but
> + * using an array, the API is designed to be extensible to support more 
> claims.
> + */
> +struct xen_memory_claim {
> +    uint64_aligned_t pages;   /* Amount of pages to be allotted to the 
> domain */
> +    uint32_t node;  /* NUMA node, or XEN_DOMCTL_CLAIM_MEMORY_NO_NODE for 
> host */
> +    uint32_t pad;                 /* padding for alignment, set to 0 on 
> input */
> +};
> +typedef struct xen_memory_claim memory_claim_t;
> +#define XEN_DOMCTL_CLAIM_MEMORY_NO_NODE    0xFFFFFFFF  /* No node: host 
> claim */
> +
> +/* Use XEN_NODE_CLAIM_INIT to initialize a memory_claim_t structure */
> +#define XEN_NODE_CLAIM_INIT(_pages, _node) { \
> +    .pages = (_pages),                  \
> +    .node = (_node),                    \
> +    .pad = 0                            \
> +}
> +DEFINE_XEN_GUEST_HANDLE(memory_claim_t);
> +
> +struct xen_domctl_claim_memory {
> +    /* IN: array of struct xen_memory_claim */
> +    XEN_GUEST_HANDLE_64(memory_claim_t) claims;
> +    /* IN: number of claims in the claims array handle. See the claims 
> field. */
> +    uint32_t nr_claims;
> +#define XEN_DOMCTL_MAX_CLAIMS UINT8_MAX /* More claims require changes in 
> Xen */
> +    uint32_t pad;                       /* padding for alignment, set it to 
> 0 */
> +};
> +
>   struct xen_domctl {
>   /* Stable domctl ops: interface_version is required to be 0.  */
>       uint32_t cmd;
> @@ -1368,6 +1404,7 @@ struct xen_domctl {
>   #define XEN_DOMCTL_gsi_permission                88
>   #define XEN_DOMCTL_set_llc_colors                89
>   #define XEN_DOMCTL_get_domain_state              90 /* stable interface */
> +#define XEN_DOMCTL_claim_memory                  91
>   #define XEN_DOMCTL_gdbsx_guestmemio            1000
>   #define XEN_DOMCTL_gdbsx_pausevcpu             1001
>   #define XEN_DOMCTL_gdbsx_unpausevcpu           1002
> @@ -1436,6 +1473,7 @@ struct xen_domctl {
>   #endif
>           struct xen_domctl_set_llc_colors    set_llc_colors;
>           struct xen_domctl_get_domain_state  get_domain_state;
> +        struct xen_domctl_claim_memory      claim_memory;
>           uint8_t                             pad[128];
>       } u;
>   };
> diff --git a/xen/include/xen/domain.h b/xen/include/xen/domain.h
> index 93c0fd00c1d7..79e8932c4530 100644
> --- a/xen/include/xen/domain.h
> +++ b/xen/include/xen/domain.h
> @@ -193,4 +193,6 @@ extern bool vmtrace_available;
>
>   extern bool vpmu_is_available;
>
> +int claim_memory(struct domain *d, const struct xen_domctl_claim_memory 
> *uinfo);
> +
>   #endif /* __XEN_DOMAIN_H__ */

Teddy


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