xen: Place vcpu_info structure into per-cpu memory
An experimental patch for Xen allows guests to place their vcpu_info
structs anywhere. We try to use this to place the vcpu_info into the
PDA, which allows direct access.
If this works, then switch to using direct access operations for
irq_enable, disable, save_fl and restore_fl.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Keir Fraser <keir@xensource.com>
diff --git a/arch/i386/xen/enlighten.c b/arch/i386/xen/enlighten.c
index 142e748..e33fa09 100644
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -61,9 +61,63 @@
struct start_info *xen_start_info;
EXPORT_SYMBOL_GPL(xen_start_info);
-void xen_vcpu_setup(int cpu)
+static /* __initdata */ struct shared_info dummy_shared_info;
+
+/*
+ * Point at some empty memory to start with. We map the real shared_info
+ * page as soon as fixmap is up and running.
+ */
+struct shared_info *HYPERVISOR_shared_info = (void *)&dummy_shared_info;
+
+/*
+ * Flag to determine whether vcpu info placement is available on all
+ * VCPUs. We assume it is to start with, and then set it to zero on
+ * the first failure. This is because it can succeed on some VCPUs
+ * and not others, since it can involve hypervisor memory allocation,
+ * or because the guest failed to guarantee all the appropriate
+ * constraints on all VCPUs (ie buffer can't cross a page boundary).
+ *
+ * Note that any particular CPU may be using a placed vcpu structure,
+ * but we can only optimise if the all are.
+ *
+ * 0: not available, 1: available
+ */
+static int have_vcpu_info_placement = 1;
+
+static void __init xen_vcpu_setup(int cpu)
{
+ struct vcpu_register_vcpu_info info;
+ int err;
+ struct vcpu_info *vcpup;
+
per_cpu(xen_vcpu, cpu) = &HYPERVISOR_shared_info->vcpu_info[cpu];
+
+ if (!have_vcpu_info_placement)
+ return; /* already tested, not available */
+
+ vcpup = &per_cpu(xen_vcpu_info, cpu);
+
+ info.mfn = virt_to_mfn(vcpup);
+ info.offset = offset_in_page(vcpup);
+
+ printk(KERN_DEBUG "trying to map vcpu_info %d at %p, mfn %x, offset %d\n",
+ cpu, vcpup, info.mfn, info.offset);
+
+ /* Check to see if the hypervisor will put the vcpu_info
+ structure where we want it, which allows direct access via
+ a percpu-variable. */
+ err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, cpu, &info);
+
+ if (err) {
+ printk(KERN_DEBUG "register_vcpu_info failed: err=%d\n", err);
+ have_vcpu_info_placement = 0;
+ } else {
+ /* This cpu is using the registered vcpu info, even if
+ later ones fail to. */
+ per_cpu(xen_vcpu, cpu) = vcpup;
+ printk(KERN_DEBUG "cpu %d using vcpu_info at %p\n",
+ cpu, vcpup);
+ }
}
static void __init xen_banner(void)
@@ -123,6 +177,20 @@
return (-flags) & X86_EFLAGS_IF;
}
+static unsigned long xen_save_fl_direct(void)
+{
+ unsigned long flags;
+
+ /* flag has opposite sense of mask */
+ flags = !x86_read_percpu(xen_vcpu_info.evtchn_upcall_mask);
+
+ /* convert to IF type flag
+ -0 -> 0x00000000
+ -1 -> 0xffffffff
+ */
+ return (-flags) & X86_EFLAGS_IF;
+}
+
static void xen_restore_fl(unsigned long flags)
{
struct vcpu_info *vcpu;
@@ -149,6 +217,25 @@
}
}
+static void xen_restore_fl_direct(unsigned long flags)
+{
+ /* convert from IF type flag */
+ flags = !(flags & X86_EFLAGS_IF);
+
+ /* This is an atomic update, so no need to worry about
+ preemption. */
+ x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, flags);
+
+ /* If we get preempted here, then any pending event will be
+ handled anyway. */
+
+ if (flags == 0) {
+ barrier(); /* unmask then check (avoid races) */
+ if (unlikely(x86_read_percpu(xen_vcpu_info.evtchn_upcall_pending)))
+ force_evtchn_callback();
+ }
+}
+
static void xen_irq_disable(void)
{
/* There's a one instruction preempt window here. We need to
@@ -159,6 +246,12 @@
preempt_enable_no_resched();
}
+static void xen_irq_disable_direct(void)
+{
+ /* Atomic update, so preemption not a concern. */
+ x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, 1);
+}
+
static void xen_irq_enable(void)
{
struct vcpu_info *vcpu;
@@ -179,6 +272,19 @@
force_evtchn_callback();
}
+static void xen_irq_enable_direct(void)
+{
+ /* Atomic update, so preemption not a concern. */
+ x86_write_percpu(xen_vcpu_info.evtchn_upcall_mask, 0);
+
+ /* Doesn't matter if we get preempted here, because any
+ pending event will get dealt with anyway. */
+
+ barrier(); /* unmask then check (avoid races) */
+ if (unlikely(x86_read_percpu(xen_vcpu_info.evtchn_upcall_pending)))
+ force_evtchn_callback();
+}
+
static void xen_safe_halt(void)
{
/* Blocking includes an implicit local_irq_enable(). */
@@ -551,11 +657,21 @@
xen_mc_issue(PARAVIRT_LAZY_MMU);
}
+static void xen_write_cr2(unsigned long cr2)
+{
+ x86_read_percpu(xen_vcpu)->arch.cr2 = cr2;
+}
+
static unsigned long xen_read_cr2(void)
{
return x86_read_percpu(xen_vcpu)->arch.cr2;
}
+static unsigned long xen_read_cr2_direct(void)
+{
+ return x86_read_percpu(xen_vcpu_info.arch.cr2);
+}
+
static void xen_write_cr4(unsigned long cr4)
{
/* never allow TSC to be disabled */
@@ -753,8 +869,27 @@
if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
BUG();
}
+}
- xen_vcpu_setup(smp_processor_id());
+/* This is called once we have the cpu_possible_map */
+void __init xen_setup_vcpu_info_placement(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ xen_vcpu_setup(cpu);
+
+ /* xen_vcpu_setup managed to place the vcpu_info within the
+ percpu area for all cpus, so make use of it */
+ if (have_vcpu_info_placement) {
+ printk(KERN_INFO "Xen: using vcpu_info placement\n");
+
+ paravirt_ops.save_fl = xen_save_fl_direct;
+ paravirt_ops.restore_fl = xen_restore_fl_direct;
+ paravirt_ops.irq_disable = xen_irq_disable_direct;
+ paravirt_ops.irq_enable = xen_irq_enable_direct;
+ paravirt_ops.read_cr2 = xen_read_cr2_direct;
+ }
}
static const struct paravirt_ops xen_paravirt_ops __initdata = {
@@ -788,7 +923,7 @@
.write_cr0 = native_write_cr0,
.read_cr2 = xen_read_cr2,
- .write_cr2 = native_write_cr2,
+ .write_cr2 = xen_write_cr2,
.read_cr3 = xen_read_cr3,
.write_cr3 = xen_write_cr3,
@@ -974,7 +1109,16 @@
/* keep using Xen gdt for now; no urgent need to change it */
x86_write_percpu(xen_cr3, __pa(pgd));
- xen_vcpu_setup(0);
+
+#ifdef CONFIG_SMP
+ /* Don't do the full vcpu_info placement stuff until we have a
+ possible map. */
+ per_cpu(xen_vcpu, 0) = &HYPERVISOR_shared_info->vcpu_info[0];
+#else
+ /* May as well do it now, since there's no good time to call
+ it later on UP. */
+ xen_setup_vcpu_info_placement();
+#endif
paravirt_ops.kernel_rpl = 1;
if (xen_feature(XENFEAT_supervisor_mode_kernel))
diff --git a/arch/i386/xen/setup.c b/arch/i386/xen/setup.c
index 18a994d..3f8684e 100644
--- a/arch/i386/xen/setup.c
+++ b/arch/i386/xen/setup.c
@@ -24,14 +24,6 @@
extern const char xen_hypervisor_callback[];
extern const char xen_failsafe_callback[];
-static __initdata struct shared_info init_shared;
-
-/*
- * Point at some empty memory to start with. We map the real shared_info
- * page as soon as fixmap is up and running.
- */
-struct shared_info *HYPERVISOR_shared_info = &init_shared;
-
unsigned long *phys_to_machine_mapping;
EXPORT_SYMBOL(phys_to_machine_mapping);
diff --git a/arch/i386/xen/smp.c b/arch/i386/xen/smp.c
index a620918..557b8e2 100644
--- a/arch/i386/xen/smp.c
+++ b/arch/i386/xen/smp.c
@@ -142,8 +142,6 @@
BUG_ON(smp_processor_id() != 0);
native_smp_prepare_boot_cpu();
- xen_vcpu_setup(0);
-
/* We've switched to the "real" per-cpu gdt, so make sure the
old memory can be recycled */
make_lowmem_page_readwrite(&per_cpu__gdt_page);
@@ -152,6 +150,8 @@
cpus_clear(cpu_sibling_map[cpu]);
cpus_clear(cpu_core_map[cpu]);
}
+
+ xen_setup_vcpu_info_placement();
}
void __init xen_smp_prepare_cpus(unsigned int max_cpus)
@@ -262,7 +262,6 @@
init_gdt(cpu);
per_cpu(current_task, cpu) = idle;
- xen_vcpu_setup(cpu);
irq_ctx_init(cpu);
xen_setup_timer(cpu);
diff --git a/arch/i386/xen/xen-ops.h b/arch/i386/xen/xen-ops.h
index 4069be8b..5b56f7f 100644
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -38,7 +38,7 @@
void __init xen_fill_possible_map(void);
-void xen_vcpu_setup(int cpu);
+void __init xen_setup_vcpu_info_placement(void);
void xen_smp_prepare_boot_cpu(void);
void xen_smp_prepare_cpus(unsigned int max_cpus);
int xen_cpu_up(unsigned int cpu);
diff --git a/include/xen/interface/vcpu.h b/include/xen/interface/vcpu.h
index c6218f1..ff61ea3 100644
--- a/include/xen/interface/vcpu.h
+++ b/include/xen/interface/vcpu.h
@@ -151,4 +151,17 @@
#define _VCPU_SSHOTTMR_future (0)
#define VCPU_SSHOTTMR_future (1U << _VCPU_SSHOTTMR_future)
+/*
+ * Register a memory location in the guest address space for the
+ * vcpu_info structure. This allows the guest to place the vcpu_info
+ * structure in a convenient place, such as in a per-cpu data area.
+ * The pointer need not be page aligned, but the structure must not
+ * cross a page boundary.
+ */
+#define VCPUOP_register_vcpu_info 10 /* arg == struct vcpu_info */
+struct vcpu_register_vcpu_info {
+ uint32_t mfn; /* mfn of page to place vcpu_info */
+ uint32_t offset; /* offset within page */
+};
+
#endif /* __XEN_PUBLIC_VCPU_H__ */