[PATCH v9 1/8] VMX: Permanently assign PI hook vmx_pi_switch_to()

[Chao Gao <chao.gao@intel.com>]

From: Feng Wu <feng.wu@intel.com>

PI hook vmx_pi_switch_to() is needed even after 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 vmx_pi_switch_to() and vmx_pi_switch_from(), 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>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
v9:
- Comments changes [per Kevin's comments]

v8: 
- Comments changes 

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 | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index d3d98da..5fa16dd 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -260,9 +260,15 @@ void vmx_pi_hooks_deassign(struct domain *d)
 
     ASSERT(d->arch.hvm_domain.pi_ops.vcpu_block);
 
+    /*
+     * Note that we don't set 'd->arch.hvm_domain.pi_ops.switch_to' to NULL
+     * here. If we deassign the hooks while the vCPU is runnable in the
+     * runqueue with 'SN' set, all the future notification event will be
+     * suppressed. Preserving the 'switch_to' hook function can make sure
+     * event time the vCPU is running the 'SN' field is cleared.
+     */
     d->arch.hvm_domain.pi_ops.vcpu_block = NULL;
     d->arch.hvm_domain.pi_ops.switch_from = NULL;
-    d->arch.hvm_domain.pi_ops.switch_to = NULL;
     d->arch.hvm_domain.pi_ops.do_resume = NULL;
 }
 
-- 
1.8.3.1


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