linux-kernel - Re: [PATCH v3 00/11] DDW + Indirect Mapping

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Date:   Thu, 22 Apr 2021 04:19:09 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Joel Stanley <joel@....id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/11] DDW + Indirect Mapping

Changes since v2:
- Some patches got removed from the series and sent by themselves,
- New tbl created for DDW + indirect mapping reserves MMIO32 space,
- Improved reserved area algorithm,
- Improved commit messages,
- Removed define for default DMA window prop name,
- Avoided some unnecessary renaming,
- Removed some unnecessary empty lines,
- Changed some code moving to forward declarations.
v2
Link: http://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=201210&state=%2A&archive=both
 

On Thu, 2021-04-22 at 04:07 -0300, Leonardo Bras wrote:
> So far it's assumed possible to map the guest RAM 1:1 to the bus, which
> works with a small number of devices. SRIOV changes it as the user can
> configure hundreds VFs and since phyp preallocates TCEs and does not
> allow IOMMU pages bigger than 64K, it has to limit the number of TCEs
> per a PE to limit waste of physical pages.
> 
> As of today, if the assumed direct mapping is not possible, DDW creation
> is skipped and the default DMA window "ibm,dma-window" is used instead.
> 
> Using the DDW instead of the default DMA window may allow to expand the
> amount of memory that can be DMA-mapped, given the number of pages (TCEs)
> may stay the same (or increase) and the default DMA window offers only
> 4k-pages while DDW may offer larger pages (4k, 64k, 16M ...).
> 
> Patch #1 replaces hard-coded 4K page size with a variable containing the
> correct page size for the window.
> 
> Patch #2 introduces iommu_table_in_use(), and replace manual bit-field
> checking where it's used. It will be used for aborting enable_ddw() if
> there is any current iommu allocation and we are trying single window
> indirect mapping.
> 
> Patch #3 introduces iommu_pseries_alloc_table() that will be helpful
> when indirect mapping needs to replace the iommu_table.
> 
> Patch #4 adds helpers for adding DDWs in the list.
> 
> Patch #5 refactors enable_ddw() so it returns if direct mapping is
> possible, instead of DMA offset. It helps for next patches on
> indirect DMA mapping and also allows DMA windows starting at 0x00.
> 
> Patch #6 bring new helper to simplify enable_ddw(), allowing
> some reorganization for introducing indirect mapping DDW.
> 
> Patch #7 adds new helper _iommu_table_setparms() and use it in other
> *setparams*() to fill iommu_table. It will also be used for creating a
> new iommu_table for indirect mapping.
> 
> Patch #8 updates remove_dma_window() to accept different property names,
> so we can introduce a new property for indirect mapping.
> 
> Patch #9 extracts find_existing_ddw_windows() into
> find_existing_ddw_windows_named(), and calls it by it's property name.
> This will be useful when the property for indirect mapping is created,
> so we can search the device-tree for both properties.
> 
> Patch #10:
> Instead of destroying the created DDW if it doesn't map the whole
> partition, make use of it instead of the default DMA window as it improves
> performance. Also, update the iommu_table and re-generate the pools.
> It introduces a new property name for DDW with indirect DMA mapping.
> 
> Patch #11:
> Does some renaming of 'direct window' to 'dma window', given the DDW
> created can now be also used in indirect mapping if direct mapping is not
> available.
> 
> All patches were tested into an LPAR with an virtio-net interface that
> allows default DMA window and DDW to coexist.
> 
> Leonardo Bras (11):
>   powerpc/pseries/iommu: Replace hard-coded page shift
>   powerpc/kernel/iommu: Add new iommu_table_in_use() helper
>   powerpc/pseries/iommu: Add iommu_pseries_alloc_table() helper
>   powerpc/pseries/iommu: Add ddw_list_new_entry() helper
>   powerpc/pseries/iommu: Allow DDW windows starting at 0x00
>   powerpc/pseries/iommu: Add ddw_property_create() and refactor
>     enable_ddw()
>   powerpc/pseries/iommu: Reorganize iommu_table_setparms*() with new
>     helper
>   powerpc/pseries/iommu: Update remove_dma_window() to accept property
>     name
>   powerpc/pseries/iommu: Find existing DDW with given property name
>   powerpc/pseries/iommu: Make use of DDW for indirect mapping
>   powerpc/pseries/iommu: Rename "direct window" to "dma window"
> 
>  arch/powerpc/include/asm/iommu.h       |   1 +
>  arch/powerpc/include/asm/tce.h         |   8 -
>  arch/powerpc/kernel/iommu.c            |  65 ++--
>  arch/powerpc/platforms/pseries/iommu.c | 504 +++++++++++++++----------
>  4 files changed, 338 insertions(+), 240 deletions(-)
>