linux-kernel - Re: [PATCH 3/5 v2] iommu/vt-d: Do deferred attachment in iommu_need

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Message-ID: <20200218155311.kt6fd25odl2gzu2t@cantor>
Date:   Tue, 18 Feb 2020 08:53:11 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org, jroedel@...e.de,
        David Woodhouse <dwmw2@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5 v2] iommu/vt-d: Do deferred attachment in
 iommu_need_mapping()

On Tue Feb 18 20, Joerg Roedel wrote:
>Hi Baolu,
>
>On Tue, Feb 18, 2020 at 10:38:14AM +0800, Lu Baolu wrote:
>> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> > index 42cdcce1602e..32f43695a22b 100644
>> > --- a/drivers/iommu/intel-iommu.c
>> > +++ b/drivers/iommu/intel-iommu.c
>> > @@ -2541,9 +2541,6 @@ static void do_deferred_attach(struct device *dev)
>> >   static struct dmar_domain *deferred_attach_domain(struct device *dev)
>> >   {
>> > -	if (unlikely(attach_deferred(dev)))
>> > -		do_deferred_attach(dev);
>> > -
>>
>> This should also be moved to the call place of deferred_attach_domain()
>> in bounce_map_single().
>>
>> bounce_map_single() assumes that devices always use DMA domain, so it
>> doesn't call iommu_need_mapping(). We could do_deferred_attach() there
>> manually.
>
>Good point, thanks for your review. Updated patch below.
>
>>From 3a5b8a66d288d86ac1fd45092e7d96f842d0cccf Mon Sep 17 00:00:00 2001
>From: Joerg Roedel <jroedel@...e.de>
>Date: Mon, 17 Feb 2020 17:20:59 +0100
>Subject: [PATCH 3/5] iommu/vt-d: Do deferred attachment in
> iommu_need_mapping()
>
>The attachment of deferred devices needs to happen before the check
>whether the device is identity mapped or not. Otherwise the check will
>return wrong results, cause warnings boot failures in kdump kernels, like
>
>	WARNING: CPU: 0 PID: 318 at ../drivers/iommu/intel-iommu.c:592 domain_get_iommu+0x61/0x70
>
>	[...]
>
>	 Call Trace:
>	  __intel_map_single+0x55/0x190
>	  intel_alloc_coherent+0xac/0x110
>	  dmam_alloc_attrs+0x50/0xa0
>	  ahci_port_start+0xfb/0x1f0 [libahci]
>	  ata_host_start.part.39+0x104/0x1e0 [libata]
>
>With the earlier check the kdump boot succeeds and a crashdump is written.
>
>Signed-off-by: Joerg Roedel <jroedel@...e.de>

Reviewed-by: Jerry Snitselaar <jsnitsel@...hat.com>