VMX: permanently assign PI hook vmx_pi_switch_to()

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>
Reviewed-by: Jan Beulich <jbeulich@suse.com>).
Acked-by: Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index b3d274bcf8c6e352a3b8cce24281c854972d77d0..e9f75d71c8736162df5dba0c69cbd44d15f13bda 100644 (file)
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -259,9 +259,22 @@ 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 since vmx_deliver_posted_intr() also use 'SN' bit
+     * as the suppression flag. Preserving the 'switch_to' hook function can
+     * clear the 'SN' bit when the vCPU becomes running next time. After
+     * that, No matter which status(runnable, running or block) the vCPU is in,
+     * the 'SN' bit will keep clear for the 'switch_from' hook function that set
+     * the 'SN' bit has been removed. At that time, the 'switch_to' hook function
+     * is also useless. Considering the function doesn't do harm to the whole
+     * system, leave it here until we find a clean solution to deassign the
+     * 'switch_to' hook function.
+     */
     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;
 }