From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Leizhen (ThunderTown)" Date: Fri, 31 May 2019 10:03:16 +0000 Subject: Re: [PATCH v8 1/7] iommu: enhance IOMMU default DMA mode build options Message-Id: <030bafab-58f5-8bb1-0533-2977d6e138b2@huawei.com> List-Id: References: <20190530034831.4184-1-thunder.leizhen@huawei.com> <20190530034831.4184-2-thunder.leizhen@huawei.com> <645bd526-4eb0-4a36-2dda-023f009247ab@huawei.com> In-Reply-To: <645bd526-4eb0-4a36-2dda-023f009247ab@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: John Garry , Jean-Philippe Brucker , Robin Murphy , Will Deacon , Joerg Roedel , Jonathan Corbet , linux-doc , Sebastian Ott , Gerald Schaefer , Martin Schwidefsky , Heiko Carstens , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Tony Luck , Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , David Woodhouse , iommu , linux-kernel , linux-s390 , linuxppc-dev , x86 , linux-ia64 Cc: Hanjun Guo , Linuxarm On 2019/5/30 20:20, John Garry wrote: > On 30/05/2019 04:48, 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. >> > > Since this was not picked up, but modulo (somtimes same) comments below: > > Reviewed-by: John Garry > >> Signed-off-by: Zhen Lei >> --- >>  drivers/iommu/Kconfig | 42 +++++++++++++++++++++++++++++++++++------- >>  drivers/iommu/iommu.c |  3 ++- >>  2 files changed, 37 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig >> index 83664db5221df02..d6a1a45f80ffbf5 100644 >> --- a/drivers/iommu/Kconfig >> +++ b/drivers/iommu/Kconfig >> @@ -75,17 +75,45 @@ 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 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_STRICT >> +    help >> +      This option allows IOMMU DMA mode to be chose at build time, to > > As before: > /s/chose/chosen/, /s/allows IOMMU/allows an IOMMU/ I'm sorry that the previous version was not modified. > >> +      override the default DMA mode of each ARCHs, removing the need to > > Again, as before: > ARCHs should be singular OK > >> +      pass in kernel parameters through command line. You can still use >> +      ARCHs specific boot options to override this option again. >> + >> +config IOMMU_DEFAULT_PASSTHROUGH >> +    bool "passthrough" >> +    help >> +      In this mode, the DMA access through IOMMU without any addresses >> +      translation. That means, the wrong or illegal DMA access can not >> +      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. > > why no advisory on how to set if unsure? Because the LAZY and STRICT have their own advantages and disadvantages. Should I say: If unsure, keep the default。 > >> + >> +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 slower in some >> +      high performace scenarios. > > and here? > >> + >> +endchoice >> + >>  config OF_IOMMU >>         def_bool y >>         depends on OF && IOMMU_API >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >> index 67ee6623f9b2a4d..56bce221285b15f 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_group { >>      struct kobject kobj; >> > > > > . >