[Xen-devel] [PATCH v6 4/7] VMX: Make sure PI is in proper state before install the hooks

[Feng Wu <feng.wu@xxxxxxxxx>]

We may hit the last ASSERT() in vmx_vcpu_block in the current code,
since vmx_vcpu_block() may get called before vmx_pi_switch_to()
has been installed or executed. Here We use cmpxchg to update
the NDST field, this can make sure we only update the NDST when
vmx_pi_switch_to() has not been called. So the NDST is in a
proper state in vmx_vcpu_block().

Suggested-by: Jan Beulich <JBeulich@xxxxxxxx>
Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
v6:
- Comments changes
- Define macro 'APIC_INVALID_DEST' for '0xffffffff'

v5:
- Use 0xffffffff as the invalid value for NDST field.

v4:
- This patch is previously called "Pause/Unpause the domain before/after 
assigning PI hooks"
- Remove the pause/unpause method
- Use cmpxchg to update NDST

 xen/arch/x86/hvm/vmx/vmcs.c       | 13 +++++--------
 xen/arch/x86/hvm/vmx/vmx.c        | 27 ++++++++++++++++++++++++++-
 xen/include/asm-x86/hvm/vmx/vmx.h |  2 ++
 3 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index 1bd875a..e8e3616 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -956,16 +956,13 @@ void virtual_vmcs_vmwrite(const struct vcpu *v, u32 
vmcs_encoding, u64 val)
  */
 static void pi_desc_init(struct vcpu *v)
 {
-    uint32_t dest;
-
     v->arch.hvm_vmx.pi_desc.nv = posted_intr_vector;
 
-    dest = cpu_physical_id(v->processor);
-
-    if ( x2apic_enabled )
-        v->arch.hvm_vmx.pi_desc.ndst = dest;
-    else
-        v->arch.hvm_vmx.pi_desc.ndst = MASK_INSR(dest, PI_xAPIC_NDST_MASK);
+    /*
+     * Mark NDST as invalid, then we can use this invalid value as a
+     * marker to whether update NDST or not in vmx_pi_hooks_assign().
+     */
+    v->arch.hvm_vmx.pi_desc.ndst = APIC_INVALID_DEST;
 }
 
 static int construct_vmcs(struct vcpu *v)
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index eb4770c..58694ce 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -206,14 +206,39 @@ static void vmx_pi_do_resume(struct vcpu *v)
 /* This function is called when pcidevs_lock is held */
 void vmx_pi_hooks_assign(struct domain *d)
 {
+    struct vcpu *v;
+
     if ( !iommu_intpost || !has_hvm_container_domain(d) )
         return;
 
     ASSERT(!d->arch.hvm_domain.vmx.vcpu_block);
 
-    d->arch.hvm_domain.vmx.vcpu_block = vmx_vcpu_block;
+    /*
+     * We carefully handle the timing here:
+     * - Install the context switch first
+     * - Then set the NDST field
+     * - Install the block and resume hooks in the end
+     *
+     * This can make sure the PI (especially the NDST feild) is
+     * in proper state when we call vmx_vcpu_block().
+     */
     d->arch.hvm_domain.vmx.pi_switch_from = vmx_pi_switch_from;
     d->arch.hvm_domain.vmx.pi_switch_to = vmx_pi_switch_to;
+
+    for_each_vcpu ( d, v )
+    {
+        unsigned int dest = cpu_physical_id(v->processor);
+        struct pi_desc *pi_desc = &v->arch.hvm_vmx.pi_desc;
+
+        /*
+         * We don't need to update NDST if vmx_pi_switch_to()
+         * has already got called.
+         */
+        (void)cmpxchg(&pi_desc->ndst, APIC_INVALID_DEST,
+                x2apic_enabled ? dest : MASK_INSR(dest, PI_xAPIC_NDST_MASK));
+    }
+
+    d->arch.hvm_domain.vmx.vcpu_block = vmx_vcpu_block;
     d->arch.hvm_domain.vmx.pi_do_resume = vmx_pi_do_resume;
 }
 
diff --git a/xen/include/asm-x86/hvm/vmx/vmx.h 
b/xen/include/asm-x86/hvm/vmx/vmx.h
index 4cdd9b1..2f0435c 100644
--- a/xen/include/asm-x86/hvm/vmx/vmx.h
+++ b/xen/include/asm-x86/hvm/vmx/vmx.h
@@ -573,6 +573,8 @@ void vmx_pi_per_cpu_init(unsigned int cpu);
 void vmx_pi_hooks_assign(struct domain *d);
 void vmx_pi_hooks_deassign(struct domain *d);
 
+#define APIC_INVALID_DEST           0xffffffff
+
 /* EPT violation qualifications definitions */
 #define _EPT_READ_VIOLATION         0
 #define EPT_READ_VIOLATION          (1UL<<_EPT_READ_VIOLATION)
-- 
2.1.0


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