[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v9 1/3] xen/domain: unify domain ID allocation
On Thu, Jun 05, 2025 at 10:58:48PM +0100, Julien Grall wrote: > Hi Denis, > > On 28/05/2025 23:50, dmkhn@xxxxxxxxx wrote: > > From: Denis Mukhin <dmkhn@xxxxxxxxx> > > > > From: Denis Mukhin <dmukhin@xxxxxxxx> > > > > Currently, hypervisor code has two different 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). > > > > The domain ID allocation covers dom0 or late hwdom, predefined domains, > > post-boot domains, excluding Xen system domains (domid >= > > DOMID_FIRST_RESERVED). > > > > 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 the bitmap. > > > > Allocation algorithm: > > - If an explicit domain ID is provided, verify its availability and use it > > if > > ID is not used; > > - If DOMID_INVALID is provided, search the range > > [0..DOMID_FIRST_RESERVED-1], > > starting from the last used ID and wrapping around as needed. It > > guarantees > > that two consecutive calls will never return the same ID. ID#0 is > > excluded > > to account for late hwdom case. > > > > 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 v8: > > - skip ID #0 in domid_alloc() to account for late hwdom > > --- > > xen/arch/arm/domain_build.c | 17 +++++--- > > xen/arch/x86/setup.c | 11 +++-- > > xen/common/device-tree/dom0less-build.c | 10 +++-- > > xen/common/domain.c | 54 +++++++++++++++++++++++++ > > xen/common/domctl.c | 42 +++---------------- > > xen/include/xen/domain.h | 3 ++ > > 6 files changed, 87 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)); > > The change in the panic here and below seems unrelated to the goal of > the patch. I am ok to keep them here, but I think it should be mentioned > in the commit message. Will do. > > > > > 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/x86/setup.c b/xen/arch/x86/setup.c > > index 1f5cb67bd0..b36ce4491b 100644 > > --- a/xen/arch/x86/setup.c > > +++ b/xen/arch/x86/setup.c > > @@ -1031,8 +1031,11 @@ 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. */ > > NIT: The two spaces were valid here. This is in fact quite common to > unambiguously mark the end of a sentence. Yep, I changed the text in comment and forgot to keep the double space. > > > + 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) ) > > @@ -1064,7 +1067,7 @@ 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"); > > } > > > > @@ -1079,7 +1082,7 @@ 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); > > diff --git a/xen/common/device-tree/dom0less-build.c > > b/xen/common/device-tree/dom0less-build.c > > index 39cb2cd5c7..a509f8fecd 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 ) > > I can't find a similar check in domid_alloc(). But if the value is > unlikely above DOMID_FIRST_RESERVED, then we would end up to allocate a > random domid. Yes, thanks. I think I need to add tools/tests with a self-test for the domain ID allocation code. > > > - 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); > > In the commit message you wrote: > > > """ > (b) Sequential IDs allocation in XEN_DOMCTL_createdomain; does not use > max_init_domid (both Arm and x86). > """ > > I read it as max_init_domid should have been moved to common code. I see > this is done in the next patch. So I would suggest to clarify this will > be handled separately. Will do. > > > > + 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..ae0c44fcbb 100644 > > --- a/xen/common/domain.c > > +++ b/xen/common/domain.c > > @@ -66,6 +66,10 @@ 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 DECLARE_BITMAP(domid_bitmap, DOMID_FIRST_RESERVED); > > + > > /* > > * 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 +1453,8 @@ 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); > > > > @@ -2405,6 +2411,54 @@ domid_t get_initial_domain_id(void) > > return hardware_domid; > > } > > > > +domid_t domid_alloc(domid_t domid) > > +{ > > + spin_lock(&domid_lock); > > + > > + if ( domid < DOMID_FIRST_RESERVED ) > > + { > > + if ( __test_and_set_bit(domid, domid_bitmap) ) > > + domid = DOMID_INVALID; > > + } > > + else > > + { > > + static domid_t domid_last; > > + /* NB: account for late hwdom case, skip ID#0 */ > > I am somewhat confused with this comment. For the late hwdom case, I > thought we were using a non-zero ID. Dom0 should also always be the > first dom0 to be reserved. Can you clarify? My current understanding is: - the ID of "domain 0" (privileged domain) can be overridden at the boot-time via hardware_domid parameter. - there's only one reserved (and configurable) domain ID == hardware_domid in the allocation range (which is 0 by default). - get_initial_domain_id() returns the reserved domain ID value (which is used in the in the follow on change to keep the change isolated). Is my understanding correct? I will update the comment. > > That said, if you want to skip to dom0. Wouldn't it be better to have > domid_last set to 1 and then ... > > > + const domid_t reserved_domid = 0;> + const bool > reserved = __test_and_set_bit(reserved_domid, domid_bitmap); > > + > > + domid = find_next_zero_bit(domid_bitmap, DOMID_FIRST_RESERVED, > > + domid_last); > > + > > + if ( domid == DOMID_FIRST_RESERVED ) > > + domid = find_next_zero_bit(domid_bitmap, DOMID_FIRST_RESERVED, > > 0); > > ... use 1 here? This would avoid to temporarily mark the domid 0 as > reserved. > > Cheers, > > -- > Julien Grall > >
|
![]() |
Lists.xenproject.org is hosted with RackSpace, monitoring our |