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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v6 1/2] xen/domain: unify domain ID allocation
On Fri, May 16, 2025 at 08:43:35AM +0000, Teddy Astie wrote:
> Hello,
>
> Le 16/05/2025 à 04:06, dmkhn@xxxxxxxxx a écrit :
> > From: Denis Mukhin <dmukhin@xxxxxxxx>
> >
> > Currently, hypervisor code has two different non-system domain ID allocation
> > implementations:
> >
> > (a) Sequential IDs allocation in dom0less Arm code based on
> > max_init_domid;
> >
> > (b) Sequential IDs allocation in XEN_DOMCTL_createdomain; does not use
> > max_init_domid (both Arm and x86).
> >
> > It makes sense to have a common helper code for such task across
> > architectures
> > (Arm and x86) and between dom0less / toolstack domU allocation.
> >
> > Wrap the domain ID allocation as an arch-independent function domid_alloc()
> > in
> > common/domain.c based on rangeset.
> >
> > Allocation algorithm:
> > - If an explicit domain ID is provided, verify its availability and
> > use it if ID is not used;
> > - Otherwise, perform an exhaustive search starting from the end of the used
> > domain ID range. domid_alloc() guarantees that two subsequent calls will
> > result in different IDs allocation.
> >
> > Initialize the domain IDs rangeset from the new domid_init() which is called
> > from arch setup code.
> >
> > Also, remove is_free_domid() helper as it is not needed now.
> >
> > No functional change intended.
> >
> > Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> > ---
> > Changes since v5:
> > - rebased
> > ---
> > xen/arch/arm/domain_build.c | 17 ++++--
> > xen/arch/arm/setup.c | 2 +
> > xen/arch/x86/setup.c | 13 +++--
> > xen/common/device-tree/dom0less-build.c | 10 ++--
> > xen/common/domain.c | 70 +++++++++++++++++++++++++
> > xen/common/domctl.c | 41 ++-------------
> > xen/include/xen/domain.h | 4 ++
> > 7 files changed, 107 insertions(+), 50 deletions(-)
> >
> > diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> > index b189a7cfae..e9d563c269 100644
> > --- a/xen/arch/arm/domain_build.c
> > +++ b/xen/arch/arm/domain_build.c
> > @@ -2010,6 +2010,7 @@ void __init create_dom0(void)
> > .grant_opts = XEN_DOMCTL_GRANT_version(opt_gnttab_max_version),
> > };
> > unsigned int flags = CDF_privileged | CDF_hardware;
> > + domid_t domid;
> > int rc;
> >
> > /* The vGIC for DOM0 is exactly emulating the hardware GIC */
> > @@ -2034,19 +2035,25 @@ void __init create_dom0(void)
> > if ( !llc_coloring_enabled )
> > flags |= CDF_directmap;
> >
> > - dom0 = domain_create(0, &dom0_cfg, flags);
> > + domid = domid_alloc(0);
> > + if ( domid == DOMID_INVALID )
> > + panic("Error allocating domain ID 0\n");
> > +
> > + dom0 = domain_create(domid, &dom0_cfg, flags);
> > if ( IS_ERR(dom0) )
> > - panic("Error creating domain 0 (rc = %ld)\n", PTR_ERR(dom0));
> > + panic("Error creating domain %d (rc = %ld)\n", domid,
> > PTR_ERR(dom0));
> >
> > if ( llc_coloring_enabled && (rc = dom0_set_llc_colors(dom0)) )
> > - panic("Error initializing LLC coloring for domain 0 (rc = %d)\n",
> > rc);
> > + panic("Error initializing LLC coloring for domain %pd (rc = %d)\n",
> > + dom0, rc);
> >
> > if ( alloc_dom0_vcpu0(dom0) == NULL )
> > - panic("Error creating domain 0 vcpu0\n");
> > + panic("Error creating domain %pdv0\n", dom0);
> >
> > rc = construct_dom0(dom0);
> > if ( rc )
> > - panic("Could not set up DOM0 guest OS (rc = %d)\n", rc);
> > + panic("Could not set up guest OS for domain %pd (rc = %d)\n",
> > + dom0, rc);
> >
> > set_xs_domain(dom0);
> > }
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> > index 10b46d0684..c3959e8d8e 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -418,6 +418,8 @@ void asmlinkage __init start_xen(unsigned long
> > fdt_paddr)
> >
> > timer_init();
> >
> > + domid_init();
> > +
> > init_idle_domain();
> >
> > rcu_init();
> > diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> > index 2518954124..02f665f520 100644
> > --- a/xen/arch/x86/setup.c
> > +++ b/xen/arch/x86/setup.c
> > @@ -1030,8 +1030,11 @@ static struct domain *__init create_dom0(struct
> > boot_info *bi)
> > if ( iommu_enabled )
> > dom0_cfg.flags |= XEN_DOMCTL_CDF_iommu;
> >
> > - /* Create initial domain. Not d0 for pvshim. */
> > - bd->domid = get_initial_domain_id();
> > + /* Allocate initial domain ID. Not d0 for pvshim. */
> > + bd->domid = domid_alloc(get_initial_domain_id());
> > + if ( bd->domid == DOMID_INVALID )
> > + panic("Error allocating domain ID %d\n", get_initial_domain_id());
> > +
> > d = domain_create(bd->domid, &dom0_cfg,
> > pv_shim ? 0 : CDF_privileged | CDF_hardware);
> > if ( IS_ERR(d) )
> > @@ -1063,7 +1066,7 @@ static struct domain *__init create_dom0(struct
> > boot_info *bi)
> >
> > if ( (strlen(acpi_param) == 0) && acpi_disabled )
> > {
> > - printk("ACPI is disabled, notifying Domain 0 (acpi=off)\n");
> > + printk("ACPI is disabled, notifying domain %pd (acpi=off)\n",
> > d);
> > safe_strcpy(acpi_param, "off");
> > }
> >
> > @@ -1078,7 +1081,7 @@ static struct domain *__init create_dom0(struct
> > boot_info *bi)
> >
> > bd->d = d;
> > if ( construct_dom0(bd) != 0 )
> > - panic("Could not construct domain 0\n");
> > + panic("Could not construct domain %pd\n", d);
> >
> > bd->cmdline = NULL;
> > xfree(cmdline);
> > @@ -1915,6 +1918,8 @@ void asmlinkage __init noreturn __start_xen(void)
> > mmio_ro_ranges = rangeset_new(NULL, "r/o mmio ranges",
> > RANGESETF_prettyprint_hex);
> >
> > + domid_init();
> > +
> > xsm_multiboot_init(bi);
> >
> > /*
> > diff --git a/xen/common/device-tree/dom0less-build.c
> > b/xen/common/device-tree/dom0less-build.c
> > index 2c56f13771..9236dbae11 100644
> > --- a/xen/common/device-tree/dom0less-build.c
> > +++ b/xen/common/device-tree/dom0less-build.c
> > @@ -850,15 +850,13 @@ void __init create_domUs(void)
> > struct xen_domctl_createdomain d_cfg = {0};
> > unsigned int flags = 0U;
> > bool has_dtb = false;
> > + domid_t domid;
> > uint32_t val;
> > int rc;
> >
> > if ( !dt_device_is_compatible(node, "xen,domain") )
> > continue;
> >
> > - if ( (max_init_domid + 1) >= DOMID_FIRST_RESERVED )
> > - panic("No more domain IDs available\n");
> > -
> > d_cfg.max_evtchn_port = 1023;
> > d_cfg.max_grant_frames = -1;
> > d_cfg.max_maptrack_frames = -1;
> > @@ -981,7 +979,11 @@ void __init create_domUs(void)
> > * very important to use the pre-increment operator to call
> > * domain_create() with a domid > 0. (domid == 0 is reserved for
> > Dom0)
> > */
> > - d = domain_create(++max_init_domid, &d_cfg, flags);
> > + domid = domid_alloc(++max_init_domid);
> > + if ( domid == DOMID_INVALID )
> > + panic("Error allocating ID for domain %s\n",
> > dt_node_name(node));
> > +
> > + d = domain_create(domid, &d_cfg, flags);
> > if ( IS_ERR(d) )
> > panic("Error creating domain %s (rc = %ld)\n",
> > dt_node_name(node), PTR_ERR(d));
> > diff --git a/xen/common/domain.c b/xen/common/domain.c
> > index abf1969e60..0ba3cdc47d 100644
> > --- a/xen/common/domain.c
> > +++ b/xen/common/domain.c
> > @@ -66,6 +66,74 @@ DEFINE_RCU_READ_LOCK(domlist_read_lock);
> > static struct domain *domain_hash[DOMAIN_HASH_SIZE];
> > struct domain *domain_list;
> >
> > +/* Non-system domain ID allocator. */
> > +static DEFINE_SPINLOCK(domid_lock);
> > +static struct rangeset *domid_rangeset;
> > +static unsigned int domid_last;
> > +
> > +void __init domid_init(void)
> > +{
> > + domid_rangeset = rangeset_new(NULL, "domid",
> > RANGESETF_prettyprint_hex);
> > + if ( !domid_rangeset )
> > + panic("cannot allocate domain ID rangeset\n");
> > +
> > + rangeset_limit(domid_rangeset, DOMID_FIRST_RESERVED);
> > +}
> > +
> > +/*
> > + * Allocate new non-system domain ID based on the hint.
> > + *
> > + * If hint is outside of valid [0..DOMID_FIRST_RESERVED - 1] range of IDs,
> > + * perform an exhaustive search starting from the end of the used domain ID
> > + * range.
> > + */
> > +domid_t domid_alloc(domid_t domid)
> > +{
> > + spin_lock(&domid_lock);
> > +
> > + if ( domid < DOMID_FIRST_RESERVED )
> > + {
> > + if ( rangeset_contains_singleton(domid_rangeset, domid) )
> > + domid = DOMID_INVALID;
> > + }
> > + else
> > + {
> > + for ( domid = domid_last + 1; domid != domid_last; domid++ )
> > + {
> > + if ( domid == DOMID_FIRST_RESERVED )
> > + domid = 0;
> > +
> > + if ( !rangeset_contains_singleton(domid_rangeset, domid) )
> > + break;
> > + }
> > +
> > + if ( domid == domid_last )
> > + domid = DOMID_INVALID;
> > + }
> > +
> > + if ( domid != DOMID_INVALID )
> > + {
> > + ASSERT(!rangeset_add_singleton(domid_rangeset, domid));
> > +
> > + if ( domid != domid_last )
> > + domid_last = domid;
> > + }
> > +
> > + spin_unlock(&domid_lock);
> > +
> > + return domid;
> > +}
>
> It's mostly a matter of implementation choice, but I am not really fan
> of relying on rangesets, which to me are meant for address ranges or
> something similar but at least large.
>
> I would rather rely on a bitmap using find_first_zero_bit+set_bit which
> avoids doing a per-domid test, and may be simpler overall. The bitmap
> size for 0x3FF0 domains is almost 4KB, which looks acceptable.
>
> I don't know what other thinks.
Thanks for taking a look!
TBH, I was initially considering using a bitmap. But then I chose use rangesets
because statically defined bitmap will increase the binary size, which may be
indesirable; and for dynamic allocation, rangeset has all convenience APIs
implemented...
>
> > +
> > +void domid_free(domid_t domid)
> > +{
> > + spin_lock(&domid_lock);
> > +
> > + if ( rangeset_contains_singleton(domid_rangeset, domid) )
> > + ASSERT(!rangeset_remove_singleton(domid_rangeset, domid));
> > +
> > + spin_unlock(&domid_lock);
> > +}
> > +
> > /*
> > * Insert a domain into the domlist/hash. This allows the domain to be
> > looked
> > * up by domid, and therefore to be the subject of hypercalls/etc.
> > @@ -1449,6 +1517,8 @@ void domain_destroy(struct domain *d)
> >
> > TRACE_TIME(TRC_DOM0_DOM_REM, d->domain_id);
> >
> > + domid_free(d->domain_id);
> > +
> > /* Remove from the domlist/hash. */
> > domlist_remove(d);
> >
> > diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> > index bfe2e1f9f0..2e02139660 100644
> > --- a/xen/common/domctl.c
> > +++ b/xen/common/domctl.c
> > @@ -49,20 +49,6 @@ static int xenctl_bitmap_to_nodemask(nodemask_t
> > *nodemask,
> > MAX_NUMNODES);
> > }
> >
> > -static inline int is_free_domid(domid_t dom)
> > -{
> > - struct domain *d;
> > -
> > - if ( dom >= DOMID_FIRST_RESERVED )
> > - return 0;
> > -
> > - if ( (d = rcu_lock_domain_by_id(dom)) == NULL )
> > - return 1;
> > -
> > - rcu_unlock_domain(d);
> > - return 0;
> > -}
> > -
> > void getdomaininfo(struct domain *d, struct xen_domctl_getdomaininfo
> > *info)
> > {
> > struct vcpu *v;
> > @@ -421,34 +407,15 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t)
> > u_domctl)
> >
> > case XEN_DOMCTL_createdomain:
> > {
> > - domid_t dom;
> > - static domid_t rover = 0;
> > + domid_t domid = domid_alloc(op->domain);
> >
> > - dom = op->domain;
> > - if ( (dom > 0) && (dom < DOMID_FIRST_RESERVED) )
> > + if ( domid == DOMID_INVALID )
> > {
> > ret = -EEXIST;
> > - if ( !is_free_domid(dom) )
> > - break;
> > - }
> > - else
> > - {
> > - for ( dom = rover + 1; dom != rover; dom++ )
> > - {
> > - if ( dom == DOMID_FIRST_RESERVED )
> > - dom = 1;
> > - if ( is_free_domid(dom) )
> > - break;
> > - }
> > -
> > - ret = -ENOMEM;
> > - if ( dom == rover )
> > - break;
> > -
> > - rover = dom;
> > + break;
> > }
> >
> > - d = domain_create(dom, &op->u.createdomain, false);
> > + d = domain_create(domid, &op->u.createdomain, false);
> > if ( IS_ERR(d) )
> > {
> > ret = PTR_ERR(d);
>
> In case the domain creation failure, we need to free the domid,
> otherwise, it would not be used anymore as considered used by the domid
> allocator.
Thanks!
>
> > diff --git a/xen/include/xen/domain.h b/xen/include/xen/domain.h
> > index e10baf2615..039bb7eeaf 100644
> > --- a/xen/include/xen/domain.h
> > +++ b/xen/include/xen/domain.h
> > @@ -38,6 +38,10 @@ void arch_get_domain_info(const struct domain *d,
> >
> > domid_t get_initial_domain_id(void);
> >
> > +void domid_init(void);
> > +void domid_free(domid_t domid);
> > +domid_t domid_alloc(domid_t domid);
> > +
> > /* CDF_* constant. Internal flags for domain creation. */
> > /* Is this a privileged domain? */
> > #define CDF_privileged (1U << 0)
>
> Teddy
>
>
> Teddy Astie | Vates XCP-ng Developer
>
> XCP-ng & Xen Orchestra - Vates solutions
>
> web: https://vates.tech
>
>
>
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