[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2] xen: arm: improve VMID allocation.
On 09/17/2013 04:56 PM, Ian Campbell wrote: > 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> Acked-by: Julien Grall <julien.grall@xxxxxxxxxx> > --- > v2: add a lock for the vmid allocator -- the p2m lock is not shared and so is > basically useless here > Add INVALID_VMID define and don't free such VMIDs, it indicates that we > weren't able to allocate a vmid for some reason > --- > xen/arch/arm/p2m.c | 71 > ++++++++++++++++++++++++++++++++++++++++++++--- > xen/arch/arm/setup.c | 2 ++ > xen/include/asm-arm/p2m.h | 3 ++ > 3 files changed, 72 insertions(+), 4 deletions(-) > > diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c > index 307c6d4..2d09fef 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 +307,59 @@ int p2m_alloc_table(struct domain *d) > return 0; > } > > +#define MAX_VMID 256 > +#define INVALID_VMID 0 /* VMID 0 is reserved */ > + > +static spinlock_t vmid_alloc_lock = SPIN_LOCK_UNLOCKED; > + > +/* VTTBR_EL2 VMID field is 8 bits. Using a bitmap here limits us to > + * 256 concurrent domains. */ > +static DECLARE_BITMAP(vmid_mask, MAX_VMID); > + > +void p2m_vmid_allocator_init(void) > +{ > + set_bit(INVALID_VMID, vmid_mask); > +} > + > +static int p2m_alloc_vmid(struct domain *d) > +{ > + struct p2m_domain *p2m = &d->arch.p2m; > + > + int rc, nr; > + > + spin_lock(&vmid_alloc_lock); > + > + nr = find_first_zero_bit(vmid_mask, MAX_VMID); > + > + ASSERT(nr != INVALID_VMID); > + > + if ( nr == MAX_VMID ) > + { > + rc = -EBUSY; > + printk(XENLOG_ERR "p2m.c: dom%d: VMID pool exhausted\n", > d->domain_id); > + goto out; > + } > + > + set_bit(nr, vmid_mask); > + > + p2m->vmid = nr; > + > + rc = 0; > + > +out: > + spin_unlock(&vmid_alloc_lock); > + return rc; > +} > + > +static void p2m_free_vmid(struct domain *d) > +{ > + struct p2m_domain *p2m = &d->arch.p2m; > + spin_lock(&vmid_alloc_lock); > + if ( p2m->vmid != INVALID_VMID ) > + clear_bit(p2m->vmid, vmid_mask); > + spin_unlock(&vmid_alloc_lock); > +} > + > void p2m_teardown(struct domain *d) > { > struct p2m_domain *p2m = &d->arch.p2m; > @@ -318,25 +372,34 @@ 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); > + p2m->vmid = INVALID_VMID; > + > + 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); > > -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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