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@citrix.com>
---
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);
--
1.8.3.2
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@citrix.com>Acked-by: Julien Grall <julien.grall@linaro.org>> --- > 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
On Tue, 2013-09-17 at 17:46 +0100, Julien Grall wrote:> 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@citrix.com> > Acked-by: Julien Grall <julien.grall@linaro.org>Thanks, applied. I dropped the final paragraph of the changelog (The existing code reserves...) since I think we decided it was true...