linux-kernel - [PATCH v9 1/7] iommu: enhance IOMMU default DMA mode build options

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Message-ID: <20190613084240.16768-2-thunder.leizhen@huawei.com>
Date:   Thu, 13 Jun 2019 16:42:34 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        John Garry <john.garry@...wei.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jonathan Corbet <corbet@....net>,
        linux-doc <linux-doc@...r.kernel.org>,
        Sebastian Ott <sebott@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        "Martin Schwidefsky" <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        x86 <x86@...nel.org>, linux-ia64 <linux-ia64@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v9 1/7] iommu: enhance IOMMU default DMA mode build options

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.

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 drivers/iommu/Kconfig | 44 ++++++++++++++++++++++++++++++++++++--------
 drivers/iommu/iommu.c |  3 ++-
 2 files changed, 38 insertions(+), 9 deletions(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 83664db5221df02..fe715fb295c6ed2 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -75,16 +75,44 @@ 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 an IOMMU DMA mode to be chosen at build time, to
+	  override the default DMA mode of each ARCH, removing the need to
+	  pass in kernel parameters through command line. You can still use
+	  ARCH specific boot options to override this option again.
 
-	  If unsure, say N here.
+	  If unsure, keep the default.
+
+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.
+
+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 slower in some
+	  high performace scenarios.
+
+endchoice
 
 config OF_IOMMU
        def_bool y
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index f9cacce909d3ae9..05171dd0bd03aee 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -31,7 +31,8 @@
 #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;
-- 
1.8.3