Subject: Re: [PATCH v6 1/1] iommu: enhance IOMMU dma mode build options

From: "Leizhen (ThunderTown)" <[email-masked]>
Date: Mon, 13 May 2019 22:04:30 +0800

On 2019/5/8 17:42, John Garry wrote:
> On 18/04/2019 14:57, Zhen Lei wrote:
>> First, add build option IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
>> opportunity to set {lazy|strict} mode as default at build time. Then put
>> the three config options in an choice, make people can only choose one of
>> the three at a time.
>>
>> The default IOMMU dma modes on each ARCHs have no change.
>>
>> Signed-off-by: Zhen Lei <[email-masked]>
>> ---
>>  arch/ia64/kernel/pci-dma.c                |  2 +-
>>  arch/powerpc/platforms/powernv/pci-ioda.c |  3 ++-
>>  arch/s390/pci/pci_dma.c                   |  2 +-
>>  arch/x86/kernel/pci-dma.c                 |  7 ++---
>>  drivers/iommu/Kconfig                     | 44 ++++++++++++++++++++++++++-----
>>  drivers/iommu/amd_iommu_init.c            |  3 ++-
>>  drivers/iommu/intel-iommu.c               |  2 +-
>>  drivers/iommu/iommu.c                     |  3 ++-
>>  8 files changed, 48 insertions(+), 18 deletions(-)
>>
>> diff --git a/arch/ia64/kernel/pci-dma.c b/arch/ia64/kernel/pci-dma.c
>> index fe988c49f01ce6a..655511dbf3c3b34 100644
>> --- a/arch/ia64/kernel/pci-dma.c
>> +++ b/arch/ia64/kernel/pci-dma.c
>> @@ -22,7 +22,7 @@
>>  int force_iommu __read_mostly;
>>  #endif
>>
>> -int iommu_pass_through;
>> +int iommu_pass_through = IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>>
>>  static int __init pci_iommu_init(void)
>>  {
>> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>> index 3ead4c237ed0ec9..383e082a9bb985c 100644
>> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
>> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>> @@ -85,7 +85,8 @@ void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
>>      va_end(args);
>>  }
>>
>> -static bool pnv_iommu_bypass_disabled __read_mostly;
>> +static bool pnv_iommu_bypass_disabled __read_mostly =
>> +            !IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>>  static bool pci_reset_phbs __read_mostly;
>>
>>  static int __init iommu_setup(char *str)
>> diff --git a/arch/s390/pci/pci_dma.c b/arch/s390/pci/pci_dma.c
>> index 9e52d1527f71495..784ad1e0acecfb1 100644
>> --- a/arch/s390/pci/pci_dma.c
>> +++ b/arch/s390/pci/pci_dma.c
>> @@ -17,7 +17,7 @@
>>
>>  static struct kmem_cache *dma_region_table_cache;
>>  static struct kmem_cache *dma_page_table_cache;
>> -static int s390_iommu_strict;
>> +static int s390_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>>
>>  static int zpci_refresh_global(struct zpci_dev *zdev)
>>  {
>> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
>> index d460998ae828514..fb2bab42a0a3173 100644
>> --- a/arch/x86/kernel/pci-dma.c
>> +++ b/arch/x86/kernel/pci-dma.c
>> @@ -43,11 +43,8 @@
>>   * It is also possible to disable by default in kernel config, and enable with
>>   * iommu=nopt at boot time.
>>   */
>> -#ifdef CONFIG_IOMMU_DEFAULT_PASSTHROUGH
>> -int iommu_pass_through __read_mostly = 1;
>> -#else
>> -int iommu_pass_through __read_mostly;
>> -#endif
>> +int iommu_pass_through __read_mostly =
>> +            IS_ENABLED(CONFIG_IOMMU_DEFAULT_PASSTHROUGH);
>>
>>  extern struct iommu_table_entry __iommu_table[], __iommu_table_end[];
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index 6f07f3b21816c64..8a1f1793cde76b4 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -74,17 +74,47 @@ config IOMMU_DEBUGFS
>>        debug/iommu directory, and then populate a subdirectory with
>>        entries as required.
>>
>> -config IOMMU_DEFAULT_PASSTHROUGH
>> -    bool "IOMMU passthrough by default"
>> +choice
>> +    prompt "IOMMU dma mode"
> 
> /s/dma/DMA/
OK

> 
> And how about add "default", as in "Default IOMMU DMA mode" or "IOMMU default DMA mode"?
Yes. I prefer "IOMMU default DMA mode".

> 
>>      depends on IOMMU_API
>> -        help
>> -      Enable passthrough by default, removing the need to pass in
>> -      iommu.passthrough=on or iommu=pt through command line. If this
>> -      is enabled, you can still disable with iommu.passthrough=off
>> -      or iommu=nopt depending on the architecture.
>> +    default IOMMU_DEFAULT_PASSTHROUGH if (PPC_POWERNV && PCI)
>> +    default IOMMU_DEFAULT_LAZY if (AMD_IOMMU || INTEL_IOMMU || S390_IOMMU)
>> +    default IOMMU_DEFAULT_STRICT
>> +    help
>> +      This option allows IOMMU dma mode to be chose at build time, to
> 
> again, capitalize acronyms, i.e. /s/dma/DMA/ (more of these above and below)
OK, I will check it all. Thanks.

> 
>> +      override the default dma mode of each ARCHs, removing the need to
>> +      pass in kernel parameters through command line. You can still use
>> +      ARCHs specific boot options to override this option again.
>> +
>> +config IOMMU_DEFAULT_PASSTHROUGH
> 
> I think that it may need to be indented, along with the other choices
There is no problem. I referred to mm/Kconfig.

> 
>> +    bool "passthrough"
>> +    help
>> +      In this mode, the dma access through IOMMU without any addresses
>> +      transformation. That means, the wrong or illegal dma access can not
> 
> transformation, or translation?
I copied from somewhere. OK, "translation" will be more clear.

> 
>> +      be caught, no error information will be reported.
>>
>>        If unsure, say N here.
>>
>> +config IOMMU_DEFAULT_LAZY
>> +    bool "lazy"
>> +    help
>> +      Support lazy mode, where for every IOMMU DMA unmap operation, the
>> +      flush operation of IOTLB and the free operation of IOVA are deferred.
>> +      They are only guaranteed to be done before the related IOVA will be
>> +      reused.
>> +
>> +config IOMMU_DEFAULT_STRICT
>> +    bool "strict"
>> +    help
>> +      For every IOMMU DMA unmap operation, the flush operation of IOTLB and
>> +      the free operation of IOVA are guaranteed to be done in the unmap
>> +      function.
>> +
>> +      This mode is safer than the two above, but it maybe slow in some high
> 
> slow, or slower? And passthough is not safe, so anything is implicitly safer.
OK. I will change it to "slower".

> 
>> +      performace scenarios.
>> +
>> +endchoice
>> +
>>  config OF_IOMMU
>>         def_bool y
>>         depends on OF && IOMMU_API
>> diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
>> index ff40ba758cf365e..16c02b08adb4cb2 100644
>> --- a/drivers/iommu/amd_iommu_init.c
>> +++ b/drivers/iommu/amd_iommu_init.c
>> @@ -166,7 +166,8 @@ struct ivmd_header {
>>                         to handle */
>>  LIST_HEAD(amd_iommu_unity_map);        /* a list of required unity mappings
>>                         we find in ACPI */
>> -bool amd_iommu_unmap_flush;        /* if true, flush on every unmap */
>> +bool amd_iommu_unmap_flush = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>> +                    /* if true, flush on every unmap */
>>
>>  LIST_HEAD(amd_iommu_list);        /* list of all AMD IOMMUs in the
>>                         system */
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index 28cb713d728ceef..0c3cc716210f35a 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -362,7 +362,7 @@ static int domain_detach_iommu(struct dmar_domain *domain,
>>
>>  static int dmar_map_gfx = 1;
>>  static int dmar_forcedac;
>> -static int intel_iommu_strict;
>> +static int intel_iommu_strict = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>>  static int intel_iommu_superpage = 1;
>>  static int intel_iommu_sm;
>>  static int iommu_identity_mapping;
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 109de67d5d727c2..0ec5952ac60e2a3 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -43,7 +43,8 @@
>>  #else
>>  static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
>>  #endif
>> -static bool iommu_dma_strict __read_mostly = true;
>> +static bool iommu_dma_strict __read_mostly =
>> +            IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
>>
>>  struct iommu_callback_data {
>>      const struct iommu_ops *ops;
>> -- 
>> 1.8.3
>>
>>
>>
>> .
>>
> 
> 
> 
> .
> 

-- 
Thanks!
BestRegards