[PATCH v7 1/6] VMX: Permanently assign PI hook vmx_pi_switch_to()

[Feng Wu <feng.wu@intel.com>]

PI hook vmx_pi_switch_to() is needed even when any previously
assigned device is detached from the domain. Since 'SN' bit is
also used to control the CPU side PI and we change the state of
SN bit in these two functions, then evaluate this bit in
vmx_deliver_posted_intr() when trying to deliver the interrupt
in posted way via software. The problem is if we deassign the
hooks while the vCPU is runnable in the runqueue with 'SN' set,
all the furture notificaton event will be suppressed. This patch
makes the hook permanently assigned.

Signed-off-by: Feng Wu <feng.wu@intel.com>
---
v7:
- comments changes.

v6:
- Adjust the comments and wording.

v5:
- Zap "pi_switch_from" hook

v4:
- Don't zap vmx_pi_switch_from() and vmx_pi_switch_to() when
any previously assigned device is detached from the domain.
- Comments changes.

 xen/arch/x86/hvm/vmx/vmx.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 3d330b6..10546af 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -222,8 +222,13 @@ void vmx_pi_hooks_deassign(struct domain *d)
 
     d->arch.hvm_domain.vmx.vcpu_block = NULL;
     d->arch.hvm_domain.vmx.pi_switch_from = NULL;
-    d->arch.hvm_domain.vmx.pi_switch_to = NULL;
     d->arch.hvm_domain.vmx.pi_do_resume = NULL;
+
+    /*
+     * In fact, we could remove 'vmx_pi_switch_to' inside itself if no new device
+     * is in the process of getting assigned and "from" hook is NULL. However,
+     * it is not straightforward to find a clear solution, so just leave it here.
+     */
 }
 
 static int vmx_domain_initialise(struct domain *d)
-- 
2.1.0


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