xen: Add support for preemption
Add Xen support for preemption. This is mostly a cleanup of existing
preempt_enable/disable calls, or just comments to explain the current
usage.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
diff --git a/arch/i386/xen/enlighten.c b/arch/i386/xen/enlighten.c
index de62d66..a1124b7 100644
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -15,6 +15,7 @@
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/preempt.h>
+#include <linux/hardirq.h>
#include <linux/percpu.h>
#include <linux/delay.h>
#include <linux/start_kernel.h>
@@ -108,11 +109,10 @@
struct vcpu_info *vcpu;
unsigned long flags;
- preempt_disable();
vcpu = x86_read_percpu(xen_vcpu);
+
/* flag has opposite sense of mask */
flags = !vcpu->evtchn_upcall_mask;
- preempt_enable();
/* convert to IF type flag
-0 -> 0x00000000
@@ -125,32 +125,35 @@
{
struct vcpu_info *vcpu;
- preempt_disable();
-
/* convert from IF type flag */
flags = !(flags & X86_EFLAGS_IF);
+
+ /* There's a one instruction preempt window here. We need to
+ make sure we're don't switch CPUs between getting the vcpu
+ pointer and updating the mask. */
+ preempt_disable();
vcpu = x86_read_percpu(xen_vcpu);
vcpu->evtchn_upcall_mask = flags;
+ preempt_enable_no_resched();
+
+ /* Doesn't matter if we get preempted here, because any
+ pending event will get dealt with anyway. */
if (flags == 0) {
- /* Unmask then check (avoid races). We're only protecting
- against updates by this CPU, so there's no need for
- anything stronger. */
- barrier();
-
+ preempt_check_resched();
+ barrier(); /* unmask then check (avoid races) */
if (unlikely(vcpu->evtchn_upcall_pending))
force_evtchn_callback();
- preempt_enable();
- } else
- preempt_enable_no_resched();
+ }
}
static void xen_irq_disable(void)
{
- struct vcpu_info *vcpu;
+ /* There's a one instruction preempt window here. We need to
+ make sure we're don't switch CPUs between getting the vcpu
+ pointer and updating the mask. */
preempt_disable();
- vcpu = x86_read_percpu(xen_vcpu);
- vcpu->evtchn_upcall_mask = 1;
+ x86_read_percpu(xen_vcpu)->evtchn_upcall_mask = 1;
preempt_enable_no_resched();
}
@@ -158,18 +161,20 @@
{
struct vcpu_info *vcpu;
+ /* There's a one instruction preempt window here. We need to
+ make sure we're don't switch CPUs between getting the vcpu
+ pointer and updating the mask. */
preempt_disable();
vcpu = x86_read_percpu(xen_vcpu);
vcpu->evtchn_upcall_mask = 0;
+ preempt_enable_no_resched();
- /* Unmask then check (avoid races). We're only protecting
- against updates by this CPU, so there's no need for
- anything stronger. */
- barrier();
+ /* 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(vcpu->evtchn_upcall_pending))
force_evtchn_callback();
- preempt_enable();
}
static void xen_safe_halt(void)
@@ -189,6 +194,8 @@
static void xen_set_lazy_mode(enum paravirt_lazy_mode mode)
{
+ BUG_ON(preemptible());
+
switch (mode) {
case PARAVIRT_LAZY_NONE:
BUG_ON(x86_read_percpu(xen_lazy_mode) == PARAVIRT_LAZY_NONE);
@@ -293,9 +300,13 @@
xmaddr_t mach_lp = virt_to_machine(lp);
u64 entry = (u64)high << 32 | low;
+ preempt_disable();
+
xen_mc_flush();
if (HYPERVISOR_update_descriptor(mach_lp.maddr, entry))
BUG();
+
+ preempt_enable();
}
static int cvt_gate_to_trap(int vector, u32 low, u32 high,
@@ -328,11 +339,13 @@
static void xen_write_idt_entry(struct desc_struct *dt, int entrynum,
u32 low, u32 high)
{
-
- int cpu = smp_processor_id();
unsigned long p = (unsigned long)&dt[entrynum];
- unsigned long start = per_cpu(idt_desc, cpu).address;
- unsigned long end = start + per_cpu(idt_desc, cpu).size + 1;
+ unsigned long start, end;
+
+ preempt_disable();
+
+ start = __get_cpu_var(idt_desc).address;
+ end = start + __get_cpu_var(idt_desc).size + 1;
xen_mc_flush();
@@ -347,6 +360,8 @@
if (HYPERVISOR_set_trap_table(info))
BUG();
}
+
+ preempt_enable();
}
static void xen_convert_trap_info(const struct Xgt_desc_struct *desc,
@@ -368,11 +383,9 @@
void xen_copy_trap_info(struct trap_info *traps)
{
- const struct Xgt_desc_struct *desc = &get_cpu_var(idt_desc);
+ const struct Xgt_desc_struct *desc = &__get_cpu_var(idt_desc);
xen_convert_trap_info(desc, traps);
-
- put_cpu_var(idt_desc);
}
/* Load a new IDT into Xen. In principle this can be per-CPU, so we
@@ -382,12 +395,11 @@
{
static DEFINE_SPINLOCK(lock);
static struct trap_info traps[257];
- int cpu = smp_processor_id();
-
- per_cpu(idt_desc, cpu) = *desc;
spin_lock(&lock);
+ __get_cpu_var(idt_desc) = *desc;
+
xen_convert_trap_info(desc, traps);
xen_mc_flush();
@@ -402,6 +414,8 @@
static void xen_write_gdt_entry(struct desc_struct *dt, int entry,
u32 low, u32 high)
{
+ preempt_disable();
+
switch ((high >> 8) & 0xff) {
case DESCTYPE_LDT:
case DESCTYPE_TSS:
@@ -418,10 +432,12 @@
}
}
+
+ preempt_enable();
}
static void xen_load_esp0(struct tss_struct *tss,
- struct thread_struct *thread)
+ struct thread_struct *thread)
{
struct multicall_space mcs = xen_mc_entry(0);
MULTI_stack_switch(mcs.mc, __KERNEL_DS, thread->esp0);
@@ -525,6 +541,8 @@
static void xen_write_cr3(unsigned long cr3)
{
+ BUG_ON(preemptible());
+
if (cr3 == x86_read_percpu(xen_cr3)) {
/* just a simple tlb flush */
xen_flush_tlb();