linux-kernel - [PATCH] iommu/vt-d: fix usage of force parameter in intel_ir_reconfigure

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Date:   Tue,  6 Mar 2018 17:39:41 -0500
From:   Jagannathan Raman <jag.raman@...cle.com>
To:     joro@...tes.org, tglx@...utronix.de
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH] iommu/vt-d: fix usage of force parameter in intel_ir_reconfigure_irte()

It was noticed that the IRTE configured for guest OS kernel
was over-written while the guest was running. As a result,
vt-d Posted Interrupts configured for the guest are not being
delivered directly, and instead bounces off the host. Every
interrupt delivery takes a VM Exit.

It was noticed that the following stack is doing the over-write:
[  147.463177]  modify_irte+0x171/0x1f0
[  147.463405]  intel_ir_set_affinity+0x5c/0x80
[  147.463641]  msi_domain_set_affinity+0x32/0x90
[  147.463881]  irq_do_set_affinity+0x37/0xd0
[  147.464125]  irq_set_affinity_locked+0x9d/0xb0
[  147.464374]  __irq_set_affinity+0x42/0x70
[  147.464627]  write_irq_affinity.isra.5+0xe1/0x110
[  147.464895]  proc_reg_write+0x38/0x70
[  147.465150]  __vfs_write+0x36/0x180
[  147.465408]  ? handle_mm_fault+0xdf/0x200
[  147.465671]  ? _cond_resched+0x15/0x30
[  147.465936]  vfs_write+0xad/0x1a0
[  147.466204]  SyS_write+0x52/0xc0
[  147.466472]  do_syscall_64+0x74/0x1a0
[  147.466744]  entry_SYSCALL_64_after_hwframe+0x3d/0xa2

reversing the sense of force check in intel_ir_reconfigure_irte()
restores proper posted interrupt functionality

Signed-off-by: Jagannathan Raman <jag.raman@...cle.com>
---
 Hi Thomas,

 I noticed that you added intel_ir_reconfigure_irte() with the
 following commit:
 d491bdff888e ("iommu/vt-d: Reevaluate vector configuration on
 activate()")

 Could you please confirm the usage of "force" parameter in
 intel_ir_reconfigure_irte()?

 drivers/iommu/intel_irq_remapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
index 66f69af..3062a15 100644
--- a/drivers/iommu/intel_irq_remapping.c
+++ b/drivers/iommu/intel_irq_remapping.c
@@ -1136,7 +1136,7 @@ static void intel_ir_reconfigure_irte(struct irq_data *irqd, bool force)
 	irte->dest_id = IRTE_DEST(cfg->dest_apicid);
 
 	/* Update the hardware only if the interrupt is in remapped mode. */
-	if (!force || ir_data->irq_2_iommu.mode == IRQ_REMAPPING)
+	if (force || ir_data->irq_2_iommu.mode == IRQ_REMAPPING)
 		modify_irte(&ir_data->irq_2_iommu, irte);
 }
 
-- 
1.8.3.1