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Subject: Re: [PATCH] iommu/vt-d: fix usage of force parameter in
 intel_ir_reconfigure_irte()
From:   Jag Raman <jag.raman@oracle.com>
In-Reply-To: <23b8f026-2dc2-e00e-98d5-f1a090e3e534@oracle.com>
Date:   Thu, 19 Apr 2018 22:17:42 -0400
Cc:     iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
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 <23b8f026-2dc2-e00e-98d5-f1a090e3e534@oracle.com>
To:     joro@8bytes.org, tglx@linutronix.de
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> On Apr 4, 2018, at 2:06 PM, Jag Raman <jag.raman@oracle.com> wrote:
>=20
>=20
>=20
> On 3/6/2018 5:39 PM, Jagannathan Raman wrote:
>> 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@oracle.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 =3D IRTE_DEST(cfg->dest_apicid);
>>    	/* Update the hardware only if the interrupt is in remapped =
mode. */
>> -	if (!force || ir_data->irq_2_iommu.mode =3D=3D IRQ_REMAPPING)
>> +	if (force || ir_data->irq_2_iommu.mode =3D=3D IRQ_REMAPPING)
>>  		modify_irte(&ir_data->irq_2_iommu, irte);
>>  }
>> =20
>=20
> *ping*

*ping*

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