Re: [PATCH v7 1/1] iommu: enhance IOMMU dma mode build options

From: John Garry
Date: Tue May 21 2019 - 09:02:07 EST

On 20/05/2019 14:59, 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 <thunder.leizhen@xxxxxxxxxx>

Apart from more minor comments, FWIW:

Reviewed-by: John Garry <john.garry@xxxxxxxxxx>

---
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);

As commented privately, I could never see this set for ia64, and it seems to exist just to keep the linker happy. Anyway, I am not sure if ever suitable to be set.


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 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

I'd say /s/allows IOMMU/allows an IOMMU/, /s/chose/chosen/

+ override the default DMA mode of each ARCHs, removing the need to

ARCHs should be singular

+ 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.
+
+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
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_group {
struct kobject kobj;
--
1.8.3



.