[Xen-changelog] [xen master] xen/arm: do not use is_running to decide whether we can write directly to the LR registers

[patchbot@xxxxxxx]

commit 071c61e7367987a9f71dc18c3c58a5dba659a5c8
Author:     Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
AuthorDate: Fri Apr 19 18:24:03 2013 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Mon Apr 22 12:34:10 2013 +0100

    xen/arm: do not use is_running to decide whether we can write directly to 
the LR registers
    
    During context switch is_running is set for the next vcpu before the
    gic state is actually saved.
    This leads to possible nasty races when interrupts need to be injected
    after is_running is set to the next vcpu but before the currently
    running gic state has been saved from the previous vcpu.
    
    Use current instead of is_running to check which one is the currently
    running vcpu: set_current is called right before __context_switch and
    schedule_tail with interrupt disabled.
    
    Re-enabled interrupts after ctxt_switch_from, so that all the context
    switch saving functions don't have to worry about receiving interrupts
    while saving state.
    
    Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/domain.c |    5 ++---
 xen/arch/arm/gic.c    |    9 ++++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index e308813..eae42af 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -213,11 +213,10 @@ static void ctxt_switch_to(struct vcpu *n)
 
 static void schedule_tail(struct vcpu *prev)
 {
-    /* Re-enable interrupts before restoring state which may fault. */
-    local_irq_enable();
-
     ctxt_switch_from(prev);
 
+    local_irq_enable();
+
     /* TODO
        update_runstate_area(current);
     */
diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index 0d1ab5a..c3887a9 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -64,12 +64,15 @@ irq_desc_t *__irq_to_desc(int irq)
 void gic_save_state(struct vcpu *v)
 {
     int i;
+    ASSERT(!local_irq_is_enabled());
 
-    spin_lock_irq(&gic.lock);
+    /* No need for spinlocks here because interrupts are disabled around
+     * this call and it only accesses struct vcpu fields that cannot be
+     * accessed simultaneously by another pCPU.
+     */
     for ( i=0; i<nr_lrs; i++)
         v->arch.gic_lr[i] = GICH[GICH_LR + i];
     v->arch.lr_mask = this_cpu(lr_mask);
-    spin_unlock_irq(&gic.lock);
     v->arch.gic_apr = GICH[GICH_APR];
     /* Disable until next VCPU scheduled */
     GICH[GICH_HCR] = 0;
@@ -524,7 +527,7 @@ void gic_set_guest_irq(struct vcpu *v, unsigned int 
virtual_irq,
 
     spin_lock_irqsave(&gic.lock, flags);
 
-    if ( v->is_running && list_empty(&v->arch.vgic.lr_pending) )
+    if ( v == current && list_empty(&v->arch.vgic.lr_pending) )
     {
         i = find_first_zero_bit(&this_cpu(lr_mask), nr_lrs);
         if (i < nr_lrs) {
--
generated by git-patchbot for /home/xen/git/xen.git#master

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