[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH] xen: arm: improve VMID allocation.
The VMID field is 8 bits. Rather than allowing only up to 256 VMs per host reboot before things start "acting strange" instead maintain a simple bitmap of used VMIDs and allocate them statically to guests upon creation. This limits us to 256 concurrent VMs which is a reasonable improvement. Eventually we will want a proper scheme to allocate VMIDs on context switch. The existing code reserves VMID==0, IIRC I thought this was "hypervisor context". Re-reading the ARM ARM I'm not spotting the bit which made me think this. However I haven't changed this behaviour here. Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx> --- NB: compile test only. --- xen/arch/arm/p2m.c | 57 +++++++++++++++++++++++++++++++++++++++++---- xen/arch/arm/setup.c | 2 ++ xen/include/asm-arm/p2m.h | 3 +++ 3 files changed, 58 insertions(+), 4 deletions(-) diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index 307c6d4..e3dfbd7 100644 --- a/xen/arch/arm/p2m.c +++ b/xen/arch/arm/p2m.c @@ -3,6 +3,7 @@ #include <xen/lib.h> #include <xen/errno.h> #include <xen/domain_page.h> +#include <xen/bitops.h> #include <asm/flushtlb.h> #include <asm/gic.h> @@ -306,6 +307,46 @@ int p2m_alloc_table(struct domain *d) return 0; } +#define MAX_VMID 256 + +/* VTTBR_EL2 VMID field is 8 bits. Using a bitmap here limits us to + * 256 concurrent domains. */ +DECLARE_BITMAP(vmid_mask, MAX_VMID); + +void p2m_vmid_allocator_init(void) +{ + /* VMID 0 is reserved */ + set_bit(0, vmid_mask); +} + +/* p2m_alloc|free_vmid must both be called with the p2m->lock */ +static int p2m_alloc_vmid(struct domain *d) +{ + struct p2m_domain *p2m = &d->arch.p2m; + + int nr = find_first_zero_bit(vmid_mask, MAX_VMID); + + ASSERT(nr > 0); /* VMID is reserved */ + + if ( nr == MAX_VMID ) + { + printk("p2m.c: dom%d: VMID pool exhausted\n", d->domain_id); + return -EBUSY; + } + + set_bit(nr, vmid_mask); + + p2m->vmid = nr; + + return 0; +} + +static void p2m_free_vmid(struct domain *d) +{ + struct p2m_domain *p2m = &d->arch.p2m; + clear_bit(p2m->vmid, vmid_mask); +} + void p2m_teardown(struct domain *d) { struct p2m_domain *p2m = &d->arch.p2m; @@ -318,25 +359,33 @@ void p2m_teardown(struct domain *d) p2m->first_level = NULL; + p2m_free_vmid(d); + spin_unlock(&p2m->lock); } int p2m_init(struct domain *d) { struct p2m_domain *p2m = &d->arch.p2m; + int rc = 0; spin_lock_init(&p2m->lock); INIT_PAGE_LIST_HEAD(&p2m->pages); - /* XXX allocate properly */ - /* Zero is reserved */ - p2m->vmid = d->domain_id + 1; + spin_lock(&p2m->lock); + + rc = p2m_alloc_vmid(d); + if ( rc != 0 ) + goto err; d->arch.vttbr = 0; p2m->first_level = NULL; - return 0; +err: + spin_unlock(&p2m->lock); + + return rc; } unsigned long gmfn_to_mfn(struct domain *d, unsigned long gpfn) diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c index 4b31623..4dfb56f 100644 --- a/xen/arch/arm/setup.c +++ b/xen/arch/arm/setup.c @@ -544,6 +544,8 @@ void __init start_xen(unsigned long boot_phys_offset, setup_virt_paging(); + p2m_vmid_allocator_init(); + softirq_init(); tasklet_subsys_init(); diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h index a00069b..c660820 100644 --- a/xen/include/asm-arm/p2m.h +++ b/xen/include/asm-arm/p2m.h @@ -20,6 +20,9 @@ struct p2m_domain { uint8_t vmid; }; +/* Initialise vmid allocator */ +void p2m_vmid_allocator_init(void); + /* Init the datastructures for later use by the p2m code */ int p2m_init(struct domain *d); -- 1.7.10.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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