Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev table if translation pre-enabled

From	Baoquan He <bhe@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev table if translation pre-enabled
Date	2017-07-28 11:10 +0200
Message-ID	<u89rs-1IQ-29@gated-at.bofh.it> (permalink)
References	<u5BWV-2C2-5@gated-at.bofh.it> <u5BWV-2C2-3@gated-at.bofh.it> <u7TmF-7Yc-3@gated-at.bofh.it>
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Hi Joerg,

On 07/27/17 at 05:55pm, Joerg Roedel wrote:
> On Fri, Jul 21, 2017 at 04:59:08PM +0800, Baoquan He wrote:
> > AMD pointed out it's unsafe to update the device-table while iommu
> > is enabled. It turns out that device-table pointer update is split
> > up into two 32bit writes in the IOMMU hardware. So updating it while
> > the IOMMU is enabled could have some nasty side effects.
> > 
> > The only way to work around this is to allocate the device-table below
> > 4GB if translation is pre-enabled in kdump kernel. If allocation failed,
> > still use the old one.
> 
> Not only for the kdump kernel. The old device table must also be below
> 4GB so that its pointer can be updated with a 32bit write.
> 
> If the old table is above 4GB you still need the second write to zero
> the upper parts of the pointer in hardware.

Do you mean the allocation of amd_iommu_dev_table in
early_amd_iommu_init() also need be addressed for 1st kernel? Seems we
don't make sure that for 1st kernel, like adding GFP_DMA32 flag when
allocate amd_iommu_dev_table in amd_iommu_dev_table
early_amd_iommu_init().

Thread

[PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev table if translation pre-enabled Baoquan He <bhe@redhat.com> - 2017-07-21 11:00 +0200
  Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Joerg Roedel <jroedel@suse.de> - 2017-07-27 18:00 +0200
    Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Baoquan He <bhe@redhat.com> - 2017-07-28 11:10 +0200
      Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Joerg Roedel <jroedel@suse.de> - 2017-07-28 13:20 +0200
        Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Baoquan He <bhe@redhat.com> - 2017-07-28 13:30 +0200
      Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Baoquan He <bhe@redhat.com> - 2017-07-28 13:20 +0200
      Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Joerg Roedel <jroedel@suse.de> - 2017-07-28 13:20 +0200
      Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Baoquan He <bhe@redhat.com> - 2017-07-31 12:20 +0200
        Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Baoquan He <bhe@redhat.com> - 2017-07-31 12:30 +0200
        Re: [PATCH v8 10/13] iommu/amd: Allocate memory below 4G for dev  table if translation pre-enabled Joerg Roedel <jroedel@suse.de> - 2017-07-31 12:30 +0200

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